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Copyright 2005, Board of Trustees, University
GULF COAST RESEARCH & EDUCATION CENTER
UNIVERSITY OF FLORIDA. IFAS
5007 60TH STREET EAST
BRADENTON, FL 34203
BRADENTON GCREC RESEARCH REPORT BRA1988-7
R. 0. MAGIE,
W. E. WATERS, G. J.
A. J. OVERMAN, J. P. GILREATH,
WILFRET, J. F. PRICE AND S. S. WOLTZ
UNIVERSITY OF FLORIOA 1
GLADIOLUS CORM PRODUCTION
Table of Contents
Introduction . . .
Cultivars . . .
Source of Cormels and Planting Stoc
Managing Cormels for Storage .
Preparation of Stocks for Planting
Gladiolus Land Management .
Drainage and Irrigation
Frost and Wind Protection
Preparation of Land (Table 1)
Crop Management . . .
Fertilization . . .
Mulches for Gladiolus . .
Weed Control . . ..
Plant Pests and Their Control .
Management of Diseases (Table 2
Management of Insects and Mites
Management of Nematodes
Corm Yields . . .
Curing and Grading
Future of Corm Production .
Capsule Precautions . .
. . 4
. . 5
. . . . . .
... . ..l
. . . .
. . . . . .
. . . .
GLADIOLUS CORM PRODUCTION
R. 0. Magie, A. J. Overman, J. P. Gilreath, W. E. Waters
G. J. Wilfret, J. F. Price, and S. S. Woltz
Gladiolus is one of the important cut flowers produced by commercial and back-
yard growers and is the most significant corm crop in many countries. There
are two separate and distinct operations involved in gladiolus production: one
is the production and management of the cormel to a flowering size corm; the
other is production and marketing of gladiolus flower spikes.
The two operations are not easily compatible for several reasons: 1) corm and
flower production each require intensive managerial attention resulting in a
tendency to neglect one or the other at some critical time during the year when
there is competition for attention, 2) the potential for the contamination of
future planting stock with the pests of the flower crop is great, 3) timing of
crop dormancy often necessitates geographical separation of the two operations
for cost-effectiveness. This report concerns information on corm production
and management to exclusion of flowering crops.
There are four stages of gladiolus growth: root development, vegetative growth,
flowering, and the growth of new corms and cormels. The production of
flowering-size corms usually requires two growing seasons: the growth of
planting stock corms from cormels, then the growth of large corms from the
Cultivars grown commercially are those in demand by wholesale and retail
florists. Cultivars planted on one farm may be different from those on another
farm, and the quantity needed of any one cultivar may change from year to year.
Cultivars suitable for commercial flower production in winter are few in number
compared to the many adapted for summer flowering. Choice of cultivars for
corm production should be revised yearly according to the market for cut
SOURCE OF CORMELS AND PLANTING STOCKS
New corm stocks are propagated from cormels which develop in clusters at the
base of maturing corms. Cormels on corms grown from cormels may be healthier
than on those grown from corms, mainly because some cormels escape cucumber
mosaic virus infection even though the mother corm was infected, and also
because hot water treatment is more effective on cormels than on large corms in
the control of Fusarium corm rot disease.
Cormels are graded into 3 or 4 sizes: large over 3/8 inch diameter; medium-
1.4 to 3/8 inch; small 3/16 to 1/4 inch; and very small less than 3/16
inch. There are 25,000 to 40,000 cormels per bushel for large size, 40,000 to
100,000 for medium size, 100,000 to 150,000 for small, and as many as 250,000
for the very small size. The weight of healthy new cormels averages 45 pounds
per bushel (35.2 liters).
Cormels or planting stocks should be purchased from corm growers, not from
flower growers in order to reduce the transfer of gladiolus pests. Most
important, the corm grower or the purchaser should hot-water treat stocks with
fungicides, following instructions on the labels. If possible, the field from
which the cormels are to be selected should be inspected for virus disease
symptoms and for nutsedge (nutgrass) weeds. The "nuts" look like cormels, so
stocks of cormels harvested from soil containing nutsedge often include these
weeds as contaminants. Nuts also are occasionally found under corm husks.
Gladiolus corms and cormels are a main source of nutsedge weed spread.
Cormel stocks should be chosen carefully, since disease organisms which occur
in the parent corms are often carried in their cormels. Those organisms
include viruses, fungi and nematodes. Thrips and their eggs also may be
carried on cormels and corms. One method of obtaining good stock of a cultivar
is to collect cormels from several sources and grow each stock separately. The
stock which demonstrates best cultivar purity, health and flower production
should be used for future propagation and gradually improved by hot water
treatment and by roguing out diseased plants in the field. Whenever possible,
cormels should be obtained from mother-stock blocks or from tissue-cultured,
In handling corms and cormels much care must be taken to avoid mixing of
cultivars or mixing of different stocks of the same cultivar. Carelessness or
lack of supervision at each step of planting, harvesting, curing, and storing
of corms may result in cultivar mixture. One cultivar or stock should be
handled at a time. Corm trays and bags should be tight enough to prevent
escape of smaller cormels. Labels which are placed inside and outside of each
package, as well as field stakes, should be marked with weather proof markers.
MANAGING CORMELS FOR STORAGE
A marked increase in the number of cormels per corm is obtained by snapping off
the flower spikes as soon as they appear. Late-planted corms (June-July) in
northern climates produce more cormels than early plantings. Cool weather
improves the quality of cormels. Cormel quality and sprouting ability can be
improved by furnishing a luxury supply of nitrogen fertilizer during the last
two months of growth. The extra nitrogen lowers the degree of cormel dormancy.
Cormels are cured by holding them in warm air at 75-80OF for one or two weeks
after they are harvested, sifted and separated into two or more sizes.
Curvularia and Fusarium diseases made the growing of cormels a hazardous
undertaking in warm climates until the hot-water treatment and the labeled use
of fungicides became available. To prepare them for the treatment, cormels are
held at room temperature (above 650F) for 6 to 8 weeks to induce enough
dormancy to permit the safe use of the hot-water treatment (HWT). Further
conditioning for this highly effective treatment against corm-borne pests,
involves soaking the dormant cormels in cool water (70-80oF) for two days
(water changed twice) during which the cormels that float are discarded. An
overnight soak in cool water acidified to pH 3 with acetic acid (vinegar) is
also effective in hydrating the cormels. The HWT is not adequately effective
unless cormels are well hydrated. The wet cormels are placed in boxes with at
least two sides screened, or in mesh bags, and the HWT is implemented
immediately after the soaking. For the HWT, use a large volume of water so
that water temperature (127-1290F) (53-540C) will be lowered only slightly by
introduction of cool cormels.
Hold cormels in the hot water for 30 minutes while stirring continuously.
Check thermometers every 3 or 4 minutes and add boiling water or cold water as
needed to adjust the temperature. At the end of 30 minutes, lower the water
temperature to 80-850F and add benomyl and captain to the dip as labeled. The
fungicides increase the effectiveness of HWT for disease control.
After treatment, pour cormels in shallow layers in clean trays to cool and dry.
Do not wash the fungicides off the cormels. Place dry cormels in cool room
(38-450F) until planting time. Trays with slatted (open) bottoms should be
lined with screen or hardware cloth fine enough to prevent loss of small
cormels and open enough to allow free movement of air through cormel masses.
Larger, hot-water-treated cormels are held in the cool room for three months or
more. Longer periods of storage may be necessary to break dormancy of small
cormels. About two weeks before planting time, cormels should be inspected for
root-bud development. Several cormels must be peeled to observe the early
root-tip swellings. Cormels should never be planted until most of them show
one or more root buds. Root-bud initiation can be hastened by moving cormels
to a warm room (75-80OF). Examine weekly for root buds. The smallest cormels
are slower to break dormancy and should be held in cool storage with good air
movement through another year unless they show root development. When cormels
show root-bud development, but the soil is not ready for planting, cormels may
be returned to cool storage until time to plant.
To avoid premature sprouting in prolonged storage of corms, they are held at a
temperature of about 40OF and a relative humidity of 65-75%. However, if air
circulation is adequate and constant through all corm masses, relative humidity
should be 90-95% in order to preserve corm moisture/weight. Corms and cormels
must be protected from freezing temperatures.
Circulation of air to all parts of storage room and through all containers is
very important. Insufficient air movement causes localized humidity
accumulation, resulting in mold growth, corm rotting, and premature sprouting
and injury of roots. Stacks of corm trays must be separated by at least two
inches from each other and from the floor and walls.
Ventilation to renew the air in commercial cool storage is required at 1 to 2
week intervals when the room is being kept closed, because carbon dioxide can
build up to high concentration, especially when corms are rotting or sprouting.
Storage room doors should be opened for an hour once or twice per week,
especially during the first 2 weeks and the last 2 weeks of the storage period.
PREPARATION OF STOCK FOR PLANTING
Cormels should be soaked in cool water (60-70OF) for one or two days just prior
to planting. Over night (16-hour) soaks are effective if a detergent and an
acid are added to the water: 3-4 ounces of detergent per 100 gallons of
acidified water (pH 3.5-4) obtained with phosphoric, acetic or muriatic acid.
Either the detergent or acid is fairly effective. Cormels which did not
receive benomyl and captain as a dip after HWT should be dipped 30 minutes in
benomyl and captain as labeled after the soak and before planting.
Corms should not be planted unless root buds are developed. Susceptibility to
diseases and soil pests is increased when dormant corms are planted because
slow emergence of roots favors attack by pathogens and nematodes. Corms
matured and harvested in warm weather have a deep dormancy. Those require 3
months or more of cool storage to develop root buds while those matured in cool
weather need only a month or more of cool storage treatment to remove dormancy.
Corms that break dormancy without cool storage should be held at about 400F
(40C) for 3 weeks or more in order to promote more uniform sprouting. Corms
harvested in cool weather have little or no dormancy remaining after a month in
cool storage; therefore, continued cool treatment is needed to prevent
premature root and shoot growth before planting. Smaller corms need longer
cool treatment than large corms to break their dormancy. Cormels need the
longest cool periods.
GLADIOLUS LAND MANAGEMENT
Most soils, if well-drained, are suitable for gladiolus. Growers prefer sandy
loams with plenty of humus. Cormel plantings are generally limited to soils
with few or no stones so that automatic corm-harvesting machines may be
used. Full sun and irrigation are required for gladiolus. A growing season
(frost-free) of at least 5 months is considered necessary.
Cormels should not be planted in soils previously planted to gladiolus unless
the soil is chemically treated to control soil-borne diseases, nematodes and
volunteer gladiolus. Land with few weed seeds, no nutgrass, and no history of
gladiolus pathogens is preferred.
Gladiolus are extremely sensitive to fluorides. They should therefore be
planted at least 25 miles from industries whose air-borne effluents contain
fluorides. Also, fluoride residues from phosphate fertilizers and well water
are absorbed by gladiolus roots and cause leaf tip burn unless the soil pH is
kept above 6.0.
Several soil factors, therefore, have considerable influence on gladiolus
growth: 1) soil moisture and drainage, 2) temperature, 3) available nutrients,
4) acidity, and 5) the soil's biological activity. Those factors affect soil
tilth, which is the physical condition and structure of the soil and its
relation to crop growth.
For those who have access to the field on an annual basis, a well planned soil
management program can assist in maintaining soil productivity for long
The ideal soil-building crop during the off-season is composed of grasses and
legumes such as alta fescue, orchardgrass, timothy, alsike clover, and woody
plants such as Aeschynomene. A deep-rooted grass like orchardgrass is
advantageous in deep soils because it pierces the lower soil profile for
improved aeration and drainage. The cover crops generally in use (rye, wheat,
and oats) are less desirable because mass and texture are inferior to the
heavier crops. Many plants now in use for cover cropping do not produce
massive root systems compared to the grasses. The value of a cover crop should
not be rated only by the amount of plant material produced above the soil
surface. A major portion of the value of a soil-building crop is in the amount
of roots produced, their distribution and depth of penetration into the soil.
Root matter and woody plants are very resistant to breakdown and help to
prevent soil compaction, encouraging good aeration and drainage.
Drainage and Irrigation
Good soil drainage is essential to maintain soil aeration and promote extensive
root systems. Mulches help to maintain aeration and soil moisture. Gladiolus
also require sufficient regular rainfall or irrigations to prevent stress and
to produce excellent corms. Gladiolus are irrigated in many ways: by overhead
sprinklers, by flooding between the planting beds, by subsurface seep (constant
water table at 12 to 20 inches), or by drip emitters. Each surface-applied
irrigation should furnish enough water to wet the sub-soil without puddling or
compacting the surface.
Since gladiolus leaves do not indicate by wilting when irrigation is required,
quick-wilting annual plants, such as Impatiens, may be grown singly in several
locations among the gladiolus plants to serve as indicators of stress.
Irrigate when they wilt. Inexpensive tensiometers could be used by commercial
growers as well as the home gardener.
Overhead irrigation should be applied early enough in the morning to wash dew
off plants; or, if later, in time for plants to dry off before night dews form.
Prolonged periods of wetting provide favorable conditions for disease spread
and should be avoided. Fungicides and other sprays should be applied only when
plants are dry.
Frost and Wind Protection
Overhead irrigation equipment should be set up and in working condition for
plantings subject to frost before corm harvest time. Sprinkling should be
started when the air temperature falls to 320F. As the water freezes on
leaves, etc. heat is released that can protect plants from freeze damage if air
temperatures do not drop too far below freezing. The ice does not protect
plants from freezing; therefore, sprinkling must continue until ice has melted.
In the event of a possible frost period, avoid cultivating the soil. Moisten
the soil surface including a 100 foot strip surrounding the planting. Warming
of air by the earth's heat radiation is more effective through moist, packed
soil. Running water between rows and in rim ditches during freezing weather
can be effective in reducing freeze damage unless strong winds occur.
Wind-blown sand may cut off small plants. Wind-driven rains may wash the soil
off the tops of high beds, exposing the corms. Thin stands of cormel plants
are especially subject to wind-blown sand injury. Sand may be held in place by
keeping the soil surface moist and by using herbicides to control weeds so that
the surface need not be disturbed. Windbreaks around cormel plantings may be
Preparation of Soil for Planting
Certain management practices can preserve the production value of gladiolus
land. Regardless of whether chemical soil treatment is to be used, growers
should manage soil conditions of the field to their advantage as long as
possible before the planting date. Plowing, discing, and rotovating the soil
for at least two months prior to planting will kill many organisms that attack
gladiolus. Moisture should be maintained in the soil during that period to
germinate weeds, which are then killed by cultivation. Moisture and
cultivation also assist in rotting old plant debris, which harbors many plant
Soils that have not had a previous crop of gladiolus usually need only nematode
control. The application of insecticide/nematicide granules to the bed and
mixed in 2-3 weeks before planting can be cost-effective in reducing nematode
Gladiolus corms and cormels often carry root-knot nematodes as well as
Stromatinia dry rot fungus and can initiate soil infestation. Stromatinia dry
rot is the most important soil-borne disease of gladiolus other than Fusarium.
Stromatinia is controlled by planting clean corms in new or fumigated soil and
by using dicloran as labeled.
After a previous crop of gladiolus, growers should consider whether the soil
should be treated to control Stromatinia and nematodes. Before going to the
expense of broadcast fumigation, furrow applications of pesticides could be
tried and compared with broadcast fumigation. Oxamyl may be mixed as labeled
into the soil before planting or applied over the planted corms/cormels in open
furrows. To control Stromatinia dry rot, follow label instructions for
dicloran applications. Dazomet granules can be used to fumigate the soil for
controlling many soil-borne pests.
Where soil fumigation is to be used, all handling of soil should be completed
before time to treat. Drainage, irrigation, and roadways should be
established. Soil amendments should be applied several months before planting
time, seedbed tilth established, and moisture at field capacity level
maintained consistently for at least two weeks before and after fumigation. If
fumigants are to be applied only in the planting beds, fertilizer may be
included as the bed is formed, treated and compacted. The soil should not be
disturbed for at least a week after placement of the fumigant. This is
important in order to obtain maximum benefits from the chemical treatment and
prevent premature dissipation of the gases.
At the time that the need for fumigation is established, growers must make
several decisions: 1) which pests are present and of economic importance; 2)
which chemical is to be used; 3) which planting pattern is to be used for the
crop, since the placement of the chemical depends on how corms are to be
planted; and 4) which method of application is suitable. In many instances for
small plantings, the easiest way to fumigate soil is to mix dazomet granules
into moist soil. The only equipment needed is a spade or plow, disc, and/or a
Table 1 offers materials and methods for soil fumigation.
For row culture, one, two, or three rows are planted per bed. High beds are
not required unless drainage is poor. Rows should run north and south, if
possible, so that both sides receive full sun, and should be spaced about 16
inches apart on the beds. The soil should be moist when the furrows are made
just before planting. Moist cormels straight from the overnight soak in
acidified detergent are spread in a wide (4-6 inch), flat furrow. A narrower
furrow is used where close cultivation is necessary to control weeds. Bulb
planters or modified onion-set planters may be used. Where moisture control
permits planting cormels to the desired 2 to 2 1/2 inch depth in a level
compacted bed, a pre-emergent herbicide may be applied immediately after
planting. Where it is difficult to keep the soil surface moist, cormels may be
covered with about 5 inches of soil, 2 inches of which must be scraped away
before sprouts have grown an inch, leaving cormels with about 2 inches of soil
cover. On this surface, pre-emergence weed control spray or granules should
be applied. However, this method of culture would be practical only where
mechanized equipment makes level furrows and does not subject the emerging
shoots to damage by the scraper.
About 120 small cormels (1/4 inch diameter) are usually planted per foot of 3-
inch-wide furrows. About 2 quarts of large cormels are needed per 100 feet (2
1/32 m), or 18 bushels per acre of double row beds constructed on 3-foot
centers. Only 8 to 12 bushels of small cormels are needed for a similar
planting. The number of cormels per foot of row may be increased in proportion
to the percentage of dead cormels found in an adequate sample from which the
husks have been removed and inspected.
A less expensive corm production system is to plant cormel rows closely in
fumigated soil. Such intensive culture reduces costs of controlling nematodes,
weeds and diseases as well as fertilizer cost. By planting rows 8 to 12 inches
apart on beds 4 feet wide, growers may produce 16,000 to 24,000 corms in 100
linear feet (30 m) of bed. Emphasis must be given to fertilization and water
control where close culture is used.
Good germination of cormels is obtained by keeping the bed moist for several
weeks after planting. Overhead irrigation should be applied as frequently as
necessary to prevent drying of soil above cormels; or a high water table can be
held by subsurface seep (ditches or tile). After the first four weeks in
plantings of large cormels or after six weeks in plantings of small cormels,
soil moisture should be gradually reduced to a moderate level until the last
month when it may be reduced further.
The soil surface is generally not cultivated except to control weeds. Soil is
swept to the base of larger gladiolus plants in order to kill weeds and give
support, but plants from cormels are often damaged by that cultivation.
Chemical or hand weeding is therefore necessary on most soils.
Table 1. Soil Treatments for Crop Protection
Follow rates, methods of application and safety measures recommended on container labels. Do not fumigate
soil near valuable plants or in poorly ventilated locations.
Pests to be
Controlled Material Application Method Remarks and Cautions
180-2000F for 30 min.
Release under gas tight
Broadcast as a drench in
1:5 dilution, then 1/4
inch overhead irrigation.
OR inject in bands 5
inches apart, 5 in. below
Broadcast and rotary
tilled to 6 inches,
followed by 1/4" irri-
Single band in crop row
6 inches below surface.
1/2 in. overhead.
Excellent control of pests. Over-pasteurization
releases salts that injure plants. Used for
cormels and high-value crops.
Excellent control of pests. A short waiting
period. Hazardous to handle. Not to be used
below 50OF (100C). Bromide residue may injure
gladiolus in heavy soils.
Excellent control during cool weather. Control
of soil moisture and surface compaction (sealing)
are critical under all conditions. Best results
when sealed with plastic. Less effective in warm
weather. Wait 2 weeks in warm, dry weather; 3
weeks in cool, wet weather before planting.
As effective as metam-sodium if soil is moistened
after applied. Must be incorporated immediately
if applied to moist soil surface because moisture
releases the gas. More effective than metam-
sodium in warm soils.
Table 1 (continued).
Pests to be
Controlled Material Application Method Remarks and Cautions
Vorlex Injected in streams 8 Soil temperature below 600F (15.60C) increases
inches apart, 6 in. below time needed to dissipate fumes from soil. Test
soil surface. if all dissipated by odor or by lettuce seed
germination test in bottle or field.
Solarization Clear plastic sheet Prepare the field as for seed bed before treat-
of soil sealed over moist soil ment, eliminating all trash before mulching.
for 8 weeks in summer. Maintain integrity of plastic sheet to trap the
Injected in streams,
12 in. apart, 8 in.
below soil surface.
into a 6" band.
Relatively low in cost. Excellent nematode
control. Lingers in wet, cool soils.
Applied as an incorporated drench at planting.
*1,3-D has been removed from the market by the manufacturer in areas of Florida south of Gilchrist County.
Small corms produced from cormels, when grown to produce large corms, are
generally planted in one or two rows per bed with rows preferably running north
and south. Depth of planting should be about 3 inches. The number of corms
planted per foot of row varies from 30 in a wide furrow to 18 in a narrow
furrow. The larger planting stock corms are planted more thinly, from 12 to 20
per foot of row. Bins on a tractor may be used to scatter corms in the furrow.
The control of weeds in planting stock and cormels is similar until the third
month, when the planting stock become strong enough to have soil swept up
against the stem. The use of herbicides is recommended under the section on
Removal of immature flower heads improves corm size; however, one or two
florets are usually allowed to open before removal of the stem so that
observations of cultivar purity and symptoms of virus infection in the corms
may be made by inspection of the flowers. Upon detection, off-types and virus-
infected corms are removed from the field. Care is taken to remove cormels
along with the corm if harvesting machinery will be used to recover cormels
from the soil. Since some viruses may be spread from plant to plant by knives
and mower blades, mowing off flower heads to improve corm size is not
recommended unless corm stocks are free of viruses that cause troublesome leaf
and flower symptoms. When mowing from one cultivar to another, mower blades
should be swabbed with denatured alcohol. During rainy hot weather, bacterial
neck rot is also spread in the cutting of flower spikes. Knives should be
sterilized in alcohol at the end of each row to reduce bacteria and virus
Development of a good root system is dependent on moist, well-drained, well-
aerated soils and an adequate supply of nutrients. Phosphorus and calcium are
particularly important for root development. For the vegetative stage,
available nitrogen is needed, along with a good supply of phosphorus, calcium,
and potash, and an adequate supply of water.
Some growers with fertile clay soils believe that the best way to fertilize
gladiolus is to build up the soil by cover-cropping with grasses and legumes.
Superphosphate and nitrogen may be applied to the cover crops to provide a well
balanced nutrient base. But, for most soils, gladiolus respond well to mineral
fertilizer applications. However, nutrient application schedules should be
governed by assays of the nutrient content of the soil such as may be obtained
by soil testing, knowledge about crop yields, and the previous fertilizer
treatments for specific soil types and climates. But ample information is
available through the County Extension Services regarding the effects of the
various fertilizer elements to help growers in choosing the right formulation
and rate of fertilizer for their soils.
Fertilizers carrying adequate nitrogen compounds have a tendency to stimulate
vegetative growth and to help produce good foliage. Too much nitrogen,
especially if out of balance with other nutrients, however, will produce soft
tissue and weak stems, especially when plants are well supplied with water.
Phosphorus, when in adequate supply, stimulates root growth and helps to
provide a better root system. Potassium increases the size and number of corms
produced in a planting.
The regulation of nutrient supplies and their balance can be accomplished
through the increase of the organic matter content of soils. Fertilization
programs are usually approached in terms of feeding the plants but it is more
accurately the feeding of the soil microflora and the plants. This may make it
possible for plants to absorb from the soil that which is needed for optimum
production, maintaining disease resistance and health. With this line of
thought, the regulation of the nutrient supplies is left to the microbial
population of the soil. The plant is naturally adapted to live on waste
products of the soil organisms. This may work for spring-summer plantings, but
cool soils in winter retard the production of waste products. The most
important factor in increasing, stimulating and maintaining a larger population
of soil microflora is the increase of their food supplies. This may be done
most economically by increasing organic matter of soil by cover cropping.
Organics from cover crops and organic mulches are very useful, but fresh
organic manures and animal by-products, unless applied several months before
planting gladiolus, often increase Fusarium corm rotting, especially when
applied under or close to corms/cormels. Ammonia, amines and other break-down
products of animal wastes stimulate the Fusarium fungus in corms and soil. Too
much nitrogen from any source is conducive to Fusarium corm rot. Nitrate-
nitrogen is the safest nitrogen source in the nutritional program. Until
pathogen-free cormels and planting stock are commonly available, the use of
mineral fertilizers is preferred during the growing season.
Large gladiolus corms may need little or no fertilizer in fertile soils which
have been augmented with leguminous cover crops. Cormels need moderate
fertilizer applications as side-dressings in addition to pre-plant fertilizer
because cormel root systems are not as extensive as those of corms and their
stored reserve of nutrients is small.
A complete fertilizer such as 6-6-6 increases the chances of supplying a
deficient nutrient. Although not an environmentally responsible practice,
under field conditions, there is little danger to the crops of using too much
fertilizer even up to applications of 1000 pounds per acre on heavy soils or
2000 on sandy soils. When using a higher nitrogen content in the fertilizer,
the rate should be lowered accordingly.
The amount of fertilizer required for cormels depends on soil type, rainfall
and density of cormels planted. Mixed fertilizer at the rate of 200 to 300
pounds per acre at each application may be sufficient on light sand soils. The
first application should be mixed about 4 inches deep in the bed prior to
planting. The remaining applications should be applied about every 3 to 6
weeks and after leaching rains. A 6-6-6 or 10-10-10 formula is ordinarily used
but slow-release fertilizers such as an 18-6-12 are preferred in easily leached
soils. Heavier soils and those enriched with leguminous cover crops may
require a 3-12-6 or 5-10-10 with fewer applications.
A slow-release fertilizer (18-6-12) may be most effective for growing cormels.
It is applied on both sides of the cormels, not under or over the planted
cormels. For light sandy soils, it is applied at the rate of 150 pounds
nitrogen per acre. The one application at planting saves labor and supplies
fertilizer elements over a 4-5 month period or longer, depending on temperature
The following micro elements may be included in gladiolus fertilizers:
manganese as MnO, 0.4%; copper as CuO for new sand land, 0.2%; magnesium as
MgO, 2%; and zinc, 0.1%. Where mancozeb foliar sprays are used and dolomite
limestone is applied to the soil, zinc, manganese and magnesium may be omitted
in the fertilizer.
Calcium is of outstanding importance to gladiolus since it regulates many plant
functions and is used in large amounts. It is important that calcium be
available in sufficient amounts right from the start of growth since this will
encourage development of a strong, functional root system. It is not prudent
to depend on the soil pH reading to indicate the presence of sufficient
calcium. Most County Extension Services provide soil calcium analysis. If the
soil pH is too low, the application of lime or limestone will usually supply
enough calcium over several months; but, if the pH is around 6.4-7.0,
superphosphate and gypsum, which contain calcium, may be broadcast or put in
planting beds without altering the pH. A level of 150-200 ppm (Spurway) of
available calcium is recommended.
Magnesium supply is adequate where dolomitic limestone is used. Otherwise,
magnesium sulfate may be used where dolomite is not needed.
Iron deficiency is identified by a yellowing of new leaves, especially the
fourth to seventh leaves. Leaf veins tend to stay greener than interveinal
areas. Flower spikes also will be yellow or pale green. Iron deficiency is a
problem in alkaline soils and older sandy loam soils that have a history of
copper accumulation from copper sprays or fertilizers. Excessive phosphate
accumulation in sandy soils may contribute to the problem also. In sandy soils
where iron is naturally low, a damaged root system often results in foliar iron
Control measures include the adjustment of soil pH to the range of 6 to 7
before planting and soil treatment with EDTA (iron ethylene diamine tetraacetic
acid) at the rate of 20 pounds active ingredient per acre if a deficiency is
found. This material should be worked into moist soil as a side dressing. If
severe iron deficiency is expected on the basis of the soil's history, 20 to 30
pounds of iron EDTA per ton of fertilizer may be used in the first 2-3
applications on cormel plantings. Other iron chelates such as EDDHA or HEDTA
or DTPA (Sequestrene) are used for more alkaline soils. Do not spray gladiolus
repeatedly with any iron compound. Sprays are relatively ineffective and may
Low copper content is characteristic of new sand lands in Florida. Copper
deficiency in gladiolus is identified by an abnormal wilting of leaves,
especially noticeable in 'Valeria' grown from cormels on copper-deficient
soils. The leaves remain green. New sand land is improved for gladiolus by
broadcasting about 20 pounds of copper sulfate per acre before planting. One
copper application is enough. Heavier rates may be used on soils with greater
organic matter content. If the deficiency develops during the growing season,
a sidedress fertilizer application supplying 10 pounds of copper sulfate per
acre may alleviate the problem. Foliar sprays containing copper are often
injurious to gladiolus.
Boron deficiency is recognized by a characteristic notching on edges of leaves,
by translucent streaks along leaf veins of some cultivars, and by blunt,
curving leaf tips. In severely deficient plants, young leaves may be stunted
and leaf edges may be thin, colorless and cracked. Cracks may develop in
flower stems. The deficiency is more likely to occur in the one to three-leaf
stage and may result from an abnormally low boron reserve in corms or cormels.
In addition to providing 0.06% B in the fertilizer, if boron deficiency
symptoms are found the grower may spray with 1 1/2 lb of borax or Solu-Bor in
100 gallons of water per acre two or three times. The total boron applied per
season should not exceed 15-20 lb of borax per acre. Spraying too frequently
with boron may cause brittle spikes. Boron is very easily leached from sandy
soils, making repeated applications necessary. Less than about 15 ppm boron in
recently matured gladiolus leaves is an indication that boron may be a limiting
MULCHES FOR GLADIOLUS
Mulching the soil around plants has improved the production of many crops
including gladiolus. Mulching reduces the labor needed for irrigation;
conserves water, fertilizer and organic matter; reduces soil erosion; and
provides non-chemical weed control. A mulch reduces the plants' stresses to
cultivation and extreme fluctuations in moisture and temperature: crop yields
There are two types of mulches: those permeable to water and those which shed
water. Organic mulches such as leaves, bark, straw and wood shavings help to
keep the soil cool and moist and allow water to penetrate readily. Sheets of
plastic, plastic-covered paper and aluminum foil have also been tested as
mulches for gladiolus plantings. Where those water-shedding coverings were
used, all fertilizer was mixed in the planting bed before the covering was
applied. Also, irrigation can be applied by 1) flooding between rows, 2)
underground seepage, or 3) drip tubes laid under the mulch sheet. Preliminary
to use as a mulch, some people cover very early spring plantings with clear
plastic sheets held above soil in order to protect early growth from frost.
he leaves are then released by cutting the plastic as the sheet is lowered to
the bed surface.
Slit plastic sheets (1 inch strips crosswise over the planted corms) have been
tried with some success, but, in general, corms/cormels are mulched usually on
both sides of the single-row bed after the plants emerge. The simplest, yet
effective, method of using non-permeable mulches for gladiolus is to lay a
narrow sheet between the rows on a 2-row bed. The fertilizer is mixed in the
strip of soil to be covered. Then the furrows are made on either side of the
fertilizer strip, about 20 inches apart for corms and 12-16 inches for cormels.
In opening the furrows, the soil is thrown away from the center of bed so that
the fertilized area is not covered. After corms/cormels are planted but not
yet covered, the strip of mulch sheet is placed along the area between rows.
The strip should be wide enough to reach down into the furrows on either side
so that the edges are held in place by soil that covers the corms but allows
emerging shoots to escape the plastic edge. The mulch is held in place without
the use of weights and weeds are thereby controlled between rows, and leaching
of fertilizer is detered.
Weed control in gladiolus is a major production problem which is especially
critical in cormel plantings where weed competition can be quite detrimental to
the crop. Effective pre-emergence weed control requires maintenance of an
undisturbed herbicide layer on and just below the soil surface. Due to the
length of the growing season, the rapid degradation rates of many herbicides,
and the disruption of the herbicide layer on the surface when fertilizer is
side-dressed, season-long weed control requires multiple applications of
herbicides. Additionally, more than one herbicide may be required to control
all of the weeds in a given field.
Few pre-emergence herbicides are labeled for use on gladiolus. Although
labeled for use in gladiolus, DCPA has provided inconsistent control over the
years and generally poor control on light sandy, low-organic-matter soils.
Napropamide is labeled for use on gladiolus, but has caused damage to the crop
in Florida tests and provided inconsistent weed control, depending on soil
moisture and rainfall after application. Trifluralin has performed similarly
in Florida and other areas with low organic matter, sandy soil. Prior to June
of 1987, many growers in Michigan and other more northern states relied upon
dinoseb; however, all registrations for that material have been cancelled in
the United States. Although research in Florida had identified several highly
effective and nonphytotoxic pre-emergence herbicides, none have been labeled
for use on gladiolus in this country as of the present time. Two of those more
effective herbicides being used on gladiolus in other countries are oryzalin
Grass weeds, especially perennial grasses such as bermudagrass, can be
especially difficult to control. Grasses often become established between the
crop plants and cannot be removed by tractor cultivation. Fortunately, we now
have post-emergence herbicides specifically designed for controlling emerged
annual and perennial grass weeds in many crops. Fluazifop-butyl, fluazifop-P-
butyl, and sethoxydim are registered for use in ornamental crops and the
labeling allows use on gladiolus. Those herbicides have been demonstrated as
being safe and efficacious in Florida-grown gladiolus. Application must be
made to annual grass plants in the 2 to 4 true-leaf stage (2 to 3 inches) for
best control. Control of perennial grasses is more difficult and requires
higher rates than annual grass weeds and may require multiple applications to
completely control the weeds. In addition to allowing a grower to control a
grass weed which escaped pre-emergence efforts, use of the post-emergence
herbicides also decreases the potential of groundwater contamination with
herbicides in areas with shallow water tables, such as in Florida.
The following herbicides were more or less toxic to gladiolus when sprayed on
the leaves: ethofumesate, napropamide, and thiobencarb. Alachlor (pre-
emergence) was toxic to shallow-planted cormels and trifluralin (pre-emergence)
injured cormels in sandy soils.
Pesticides, such as herbicides used on previous crops, may leave residues in
soil that reduce root growth. Activated charcoal has improved growth of cormel
plants where herbicides and fumigants were used in previous years. A specially
treated charcoal, which is much more absorptive than common charcoal, can be
used. It is generally available as "Gro-Safe".
Gro-Safe may be mixed in the bottom of furrows or trenches before cormels are
PLANT PESTS AND THEIR CONTROL
Gladiolus, like most other plants, are attacked by fungal and bacterial
pathogens as well as insects, mites, and nematodes. Some soil- and corm-borne
pathogens attack roots and corms; others cause leaf and flower damage. Once
contaminated by various pests carried on corms and cormels, soils remain
infested to affect future plantings for many years.
Sanitary practices in crop management help to avoid introduction and spread of
some important diseases as well as weed, nematode and insect pests. The cost of
sanitation is generally minor compared to the benefits obtained. Two factors
in sanitation are using cormels and planting stocks that were treated in hot
water with the labeled fungicides and avoiding the introduction of untreated
cormels and corms. Also important is the destruction of diseased stocks and
the improvement of good stocks by roguing. Stocks showing more than one
percent of virus-infected plants should not be used for propagation if
healthier stocks are available. Healthy "mother block" stocks should be
isolated and monitored carefully.
All refuse from cleaning and sorting of corms should be destroyed by burning or
deep burial outside of the fields. Before re-using trays, bags, etc., in which
cormels or corms were stored, scrub and soak them in a solution of one gallon
of commercial bleach (5% sodium hypochlorite) in 10 gallons of water.
Commercial bleach will not completely sanitize wood trays; plastic trays are
therefore a wiser choice.
Cormels to be planted in fumigated soil should not be contaminated with soil or
refuse. Machinery and tools should be cleaned and sterilized with the chlorine
solution so that untreated soil is not carried to fumigated planting beds.
Sieves and graders should be sterilized between corm lots. If cormels are
soaked in plain water, treat them promptly in water with the labeled
Management of Disease
Gladiolus plants grown from cormels and planting stocks are injured more often
by diseases, nematodes, and insects than the larger plants developed from
flowering-size corms. The best and least expensive control programs depend for
their success on early and correct diagnosis of the problem and prompt
application of recommended control measures.
Check lists of plant and corm symptoms of damage are given in Tables 2 and 3 to
help in disease recognition. Grower organizations may borrow 35 mm color
slides of disease symptoms from Mr. Henry Wagner, NAGC Film Librarian, 1412
Southridge Drive, Brea, CA 92621; borrowers pay postage.
Table 2. Check List of Disease Symptoms and Environmental Damage on Growing Plants
Appearance of Plants Cause of Trouble Comments
Brown, elongated, oval spots on petals
and younger leaves. Young leaf spots
are tan within a reddish brown ring
which is bordered by a yellowish halo.
Spots enlarge rapidly, especially
along leaf edge.
Brown rot at soil line; plants toppled.
Numerous round, reddish brown spots of
all sizes, mostly small; smallest are
visible only on top side of leaf.
Flower spots are water-soaked. Also
t bud rot.
Small, roundish, translucent yellow
spots with a red dot in center on
green parts of plant. On some
cultivars, spots are larger, oval and
light brown. Spots show on both sides
Minute brown spots turning reddish-
brown with a well-defined, light gray
center dotted with numerous black, pin-
Orange-brown rust spots showing on both
leaf surfaces. Spots are elongated
across width of leaves (transverse to
leaf axis). In autumn, spots turn
black with over-wintering spores.
Curvularia disease-Curvularia trifolii
(Kauff.) Boed. f. sp. gladioli Parm. &
Botrytis gray mold, leaf spot, corm rot,
and flower rot caused by B. gladiolorum
Timmermans. Produces millions of spores
Stemphylium leaf spot or "Red Spot".
Probably caused by Stemphylium botryosum
The hard rot fungus:
The "transverse" or brown rust disease.
Uromyces transversalis (Theum.) Winter.
A warm weather disease.
Small clusters of black
spores near centers of
larger spots. Small spots
lie transversely to leaf
A cool weather disease.
Gray mold (seen best when
wet with dew) is found on
rotted flowers, necks and
larger leaf spots.
A cool weather disease
that spreads rapidly from
susceptible to less
Attacks mature leaves,
turning them yellow.
Septoria and Stemphylium
diseases are seldom seen
on plants sprayed for
other leaf spot control.
This most dreaded of the
rust diseases of the glad-
iolus spread from Africa
to southern Europe and
South America. Notify
your County Extension
Service personnel if
disease is found in North
Table 2 (Continued).
Appearance of Plants Cause of Trouble Comments
Late blooming, stunted spikes; narrow
leaves, often yellowed; curved, "cow-
horn" leaves from large corms with rot;
neck rot separates leaves from corm.
"Blind" plants. Dark green stem, one-
sided development of florets.
Neck rot penetrating all leaf bases,
with sharp, musty odor. Plant stays
attached to corm when pulled. Yellow
leaves and short spikes. Cormel plants
attacked in groups. Very small black
0 specks (sclerotia) seen in dead root/
neck tissues with magnifying glass.
Neck rot, often affecting inner leaves
first. Small, rust colored spots on
inner leaves becoming dull brown.
Leaf spots round, rusty brown. Husk
lesions become black, destroying tissue
between leaf veins.
Dark, water-soaked, rectangular lesions
between leaf veins. Lesions turn light
brown and a varnish-like exudate may be
Neck rot and root rot.
Fusarium disease: F. oxysporum (Massey)
Snyder & Hanson, a soil fungus that is
tough and variable.
The dry rot fungus which lives in soil
for many years as sclerotia.
Stromatinia gladioli (Crayt.) Whetz.
Bacterial scab of corms, neck rot, and
leaf spots. Pseudomonas marginata
(McCull.) Stapp syn P. gladioli.
Xanthomonas campestris pv. gummisudans
(McCull.) Young, Dye, et al. Bacterial
Sclerotium rolfsii Sacc. & Rhizoctonia
sp., common soil fungi.
Affected plants usually
not grouped. Carried in
corms and soil. Symptoms
vary greatly according to
cultivar, the environment
and the particular
A cool weather disease.
The most troublesome, soil-
borne problem of gladiolus.
Sclerotia are distinctive
for identification. Infec-
tion spreads from the soil
or corms and from small
plant to small plant.
Damaging in hot, wet
weather. Spread by rain,
cutting knife, etc.
Occurs on small, crowded
plants, but rarely found.
A warm weather disease.
S. rolfsii attacks in warm,
arFy weather. Rhizoctonia
spreads from residues of
previous crops beans,
legumes, root crops
Table 2 (Continued).
Appearance of Plants Cause of Trouble Comments
Light green mosaic or whitish fleck-
ing on leaves; flower petal blotched
or flecked with lighter or darker
colors; or short spikes and small
plants. "White Break" of flowers.
Multiple weak shoots and many short,
weak roots (Western Aster Yellows).
The Eastern strain causes only extra
weak shoots. Note the abnormal ap-
pearance of corm core in cross section
of grassy-top & hairy root corms.
Yellow bands formed at ground level on
first leaves, often marking daily
growth. Light brown patches on sunny
side of short sheath leaves.
Leaf tip burn or fluoride scorch,
noticeable after second leaf. If the
burn on some cultivars is below leaf
tip and on one side, fluoride scorch
Bean yellow mosaic or cucumber mosaic,
stunt virus, ring spot viruses and two
or more viruses in one corm.
Mycoplasm-like organisms; not a virus.
There are two maladies: "Grassy-top &
Hairy Root" (western aster yellows)
and the eastern strain of aster
Bright sun after a cool night with
active growth of small plant.
Low soil pH; poor root action; fluoride
scorch; root damage due to nematodes,
One or more viruses are
carried in all corm stocks
tested so far, but corms
from tissue culture or
recently from seed may be
Spread by certain leaf
hoppers from other crops in
warm dry weather. "Grassy-
top" is cured by warm-water
corm treatment in Holland.
Yellow bands usually turn
green, but leaf may be
pinched in at the band.
Tip burn may increase as
soil pH falls below 5.8.
Severe scorch is associated
with fluorides in air or
Table 3. Check List of Disease Symptoms and Tissue Damage on Roots and Harvested Corms
Appearance of corms and roots Cause of Trouble Comments
Stunted corms with dark-stained husks,
sometimes shredded at top; black,
shallow, scurfy dry rot along husk
scars on upper half of corm. Yellow-
ing and sloughing of root cortex
("bark") is an early sign of disease.
Rotting of roots results in short
Soft, watery rot changing to a spongy
corm rot; found in core, in vascular
tissue, or in entire corm. Dries to
light-weight, unshriveled corm with
^ white mold between husks. Large
black sclerotia are found on some corms.
Small to large, depressed, irregular
shaped, dark brown spots, mostly
shallow, but occasionally invading
vascular tissue. Found on top and
sides of corms.
A soft rot in soil, but after harvest,
a brown, firm, tough rot extending
into corm, often along vascular tissue.
Often found at one side of core at
base. Reduces corm to stone-like mummy
Reddish-brown sunken spots with hard
surface and often concentric rings.
Often covered with greenish-blue
The dry rot fungus: Stromatinia
gladioli (Drayt.) Whetz.
Botrytis soft rot B. gladiolorum
Curvularia disease, a soil fungus;
C. trifolii (Kauff.) Boed. f. sp.
gladioli Parm. & Luttrell.
Fusarium disease F. oxysporum f. sp.
gladioli (Massey) Sny. & Hans., a soil
Penicillium corm rot P. gladioli
McCull. & Thom.
Disease is identified by
the distinctive, small,
black sclerotia seen under
cuticle of roots and neck
with help of magnifying
Rotting may not begin until
after corms have been in
cool storage. Rot spreads
from corm to corm, forming
nests of rotted corms.
Spots may be small or
invisible at harvest time.
Often associated with
Fusarium rot in the larger
Rotted tissue blends into
the healthy tissue.
Symptoms vary greatly. Most
infections are latent and
Small, light brown
sclerotia develop below
surface. Occurs in corms
harvested in cold, moist
weather & poorly cured.
Table 3 (Continued).
Appearance of corms and roots Cause of Trouble Comments
Small, reddish-brown to black, water-
soaked spots, later becoming large with
wrinkled surface. Decay may not
go any deeper than 1/4 inch, but a hard
mummy may develop.
A stringy white mold that kills plants
and cormels before harvest. The tan
sclerotia resemble radish seed in size
Cores rotted out or depressed.
^ Called "doughnut" corms.
Web-like, white mycelial growth causing
red-brown lesions and shredded leaf
bases. Contractile roots show dark
brown lesions or are cut off short.
Dull and dark husks (cataphylls).
Husks are dark, split, eroded at base.
Depressed, round scabs, which are some-
times covered with a varnish-like
scale; scabs leave a clean, bowl-
shaped depression when lifted.
The hard rot fungus Septoria gladioli
Southern blight Sclerotium rolfsii
Penicillium funiculosum Thom, other
fungi and bacteria.
Rhizoctonia solani, a soil fungus.
Soil bacteria and fungi attack husks
in warm, wet soils.
Pseudomonas marginata (McCull.) Stapp
causes bacterial scab on corms.
Minute, black fungus fruit-
ing bodies of pin-point
size may be seen on
Occasionally found in dry,
Occurs where large corms
are dug from warm, moist
soils; may be due to
Spreads from crop debris in
soil. Usually due to
previous crop of beans,
legumes, etc. that had not
Occurs in early summer
harvest. May indicate
Corm scabs are usually
associated with insect and
soil mite injuries and with
bacterial neck rot.
Table 3 (Continued).
Appearance of corms and roots Cause of Trouble Comments
Moldy corms in storage, usually a
white or greenish mold.
Surface depressions and internal brown
streaks in corms.
Discolored areas, especially around
base and where corm is not protected
by husks. The underlying tissue is
often chalky and white.
Large, sunken, brown lesions on side
of corm exposed to sun; the brown
tissue is leathery.
Common mold fungi in still air of cool
Cucumber mosaic virus infection.
Bruises and cuts made during corm
harvest or later.
Sun burn, often followed by a fuzzy,
black mold called Rhizopus arrhizus
Root swellings may be
killed by mold. Maintain
cool room humidity, but
move air forcefully.
Symptoms of cucumber mosaic
disease may appear in corms
of 'Friendship' but not
many other cultivars.
Bruised corms may flower
normally unless infected.
Bruising of small corms
results in extreme desic-
Corms burn from exposure to
sun during summer harvest.
The Curvularia fungus, carried on corms and cormels and surviving in soil
between crops, damages small plants severely by rotting the roots and leaves
and attacking the new corms. Curvularia is the main disease of leaves and
flowers in warm, wet weather. Neck rot and death of small plants may occur
without above-ground infections. However, the fungus is active below and above
ground. It is most damaging in warm weather but often appears in other
Regular and thorough spraying with mancozeb, maneb + zinc salt, maneb, or
chlorothalonil before the disease appears is fairly effective in controlling
Curvularia. After infections have spread, the disease is very difficult to
control: twice-weekly spraying with mancozeb or weekly spraying with
chlorothalonil may be necessary.
The Botrytis fungus attacks leaves, flowers and corms. Twice-weekly sprayings
with mancozeb or chlorothalonil, or weekly sprays of vinclozolin plus mancozeb,
or iprodione are very effective in control of this disease.
Stemphylium leaf spot develops on the older leaves following dews and fogs.
Spraying to control the other leaf spot diseases has been very effective in
preventing the appearance of Stemphylium. Anilazine is most effective in its
Management of Insect and Mite Pests
Numerous insects and mites can affect the gladiolus and its production of
quality corms, however only a few groups of the pests normally may be expected.
Those are discussed here along with suggestions for controls. Where pesticides
are named, only the common names are used.
Several species of thrips can be important to gladiolus corm production. These
include various flower thrips and the more serious gladiolus thrips (Thrips
simplex (Morison)) that attacks both the stored corms and the flower spike.
Gladiolus thrips may cause silvery scars on leaves and flowers from feeding
done as the flowers are maturing. Small, yellow, immature thrips and larger
black ones may be active under tissues surrounding corms in storage. Affected
corms may desiccate and become unthrifty; they also serve as sources of thrips
for problems later in the field.
Gladiolus thrips management requires sanitation practices that eliminate
gladiolus refuse, an important site for overwintering of the pest. When this
is performed and only corms free of the thrips are planted, problems from this
pest can be greatly reduced. Insecticides permitted for thrips control
include:acephate, bendiocarb, carbaryl, chlorpyrifos, diazinon, dimethoate,
malathion, methomyl, oxamyl, permethrin, and pyrethrins with piperonyl
Wireworms, larvae of click beetles, live in the soil and may feed on the corm
and its emerging leaves. On the corm, damage is often recognized as round or
oval scabs and holes on the corm's sides; scabs may lift out easily, leaving
clean, bowl-shaped depressions. Holes in the corm may be partly covered with a
"skin". On developing leaves, wireworm damage is often expressed as a vertical
row of holes caused by the wireworm's intermittent feeding; bacterial neck rot
may follow these injuries in warm wet weather.
Wireworms are most destructive when a gladiolus crop is planted in a site
recently growing grass sod. Soil fumigants applied to control diseases and
nematodes usually also control wireworms. Lindane dusted on corms at planting
can protect corms from wireworm damage.
Several lepidopterous larvae ("worms") exist that may attack the above- ground
gladiolus parts and must be controlled when sufficiently numerous. These
include cabbage loopers, various armyworms and corn earworms. Pesticides
available for control of specific lepidopterous larvae on gladiolus include:
acephate, Bacillus thuringiensis, chlorpyrifos, methomyl, pyrethrins with
piperonyl butoxide, and trichlorfon.
Japanese beetles may attack gladiolus spikes and leaves in the summertime,
particularly in the northeastern United States. Where these insects are
active, little can be done to prevent losses, except to remove beetles by hand
where practical, or treat infested plants with pesticides such as acephate,
carbaryl, malathion, methoxychlor or oxamyl.
Aphids can be especially numerous on young gladiolus spikes, and are most
harmful when they vector plant viruses. The following insecticides are
available for control of aphids: acephate, bendiocarb, chlorpyrifos, diazinon,
dimethoate, malathion, methomyl, oxamyl, permethrin and pyrethrins with
Spidermites will attack gladiolus leaves and spikes occasionally, sucking
tissues dry; spidermite damage seems to occur most often in hot, dry periods.
During these times, bendiocarb, ethion, fenbutatin-oxide and oxythioquinox can
be useful to reduce damage.
Management of Nematodes
Root-knot nematodes (Meloidogyne spp.) are the most important nematode species
associated with gladiolus. Root-knot is an endoparasite widespread in many
soil types in many climates. Cultivars differ in sensitivity to the invasion
of the plant by the nematode, although no commercial cultivar is known to be
immune to attack. The second-stage juvenile of the root-knot nematode has been
found in the roots of gladiolus, in the cormels, corms, stolons, even in the
leaves which, below ground, become the husk of the developing corm.
When the nematodes invade the plant, swellings or tumors appear at the site on
the roots and often in the storage tissue adjacent to the leaf nodes on corms;
warts and jelly-like rot develop at the base of the small corms. Newly
harvested corms and cormels seem spongy until the jelly-like rot petrifies,
resulting in a chalky texture of the storage tissue.
Root-knot nematodes, because they are harboured within the corms and cormels,
survive storage and are moved with the planting stock into next year's field of
production in all life stages. Hot water treatment controls these nematodes in
the corm tissue and, when properly executed, interrupts the yearly cycle of
root-knot accompanying the corms into the new crops.
In sandy soils, the shallow rooted cormels may be damaged by the sting nematode
(Belonolaimus longicaudatus Rau). An ectoparasite, the sting nematode
restricts root development, thereby retarding growth of the foliage as well as
quality corm production. These nematodes are easily controlled with soil
fumigation and do not accompany the cleaned corms into storage.
Control of nematode populations in the field can be achieved with soil
fumigation using materials and procedures displayed in Table 1.
Over 30 corms larger than 1/2 inch in diameter are harvested per foot of row in
a well-managed cormel planting. With some cultivars planted in single-row beds
on 3 foot centers, about 750,000 corms are harvested per acre; with double
rows, about 1 1/2 million corms; and from closely planted seed beds, about 2 to
3 million corms. The size of corms produced depends mainly on cultivar,
season, and growing conditions. The number of flowering-size corms produced
per acre from No. 5 and 6 corms is about 175,000 for single rows to 350,000 for
double-row beds with 3-foot centers.
Corms are usually lifted before the leaves turn yellow, since corms are more
susceptible to disease infections when left in soil after roots or tops die.
Maximum corm size is attained in five to seven months after planting cormels.
Corms maturing in cool weather enlarge rapidly compared to warm-weather corms.
Corms from planting stock as well as those from cormels are usually ready to
harvest three weeks after the larger cormels darken but while the smaller
cormels are still white. The soil should be permitted to dry the last week or
two before harvest to facilitate digging.
For best utilization of labor and equipment, harvesting may be started early
before maximum corm size is made, or about 5 months after planting. Although
corm size is increased if harvest is delayed, more cormels will be lost by
shattering unless special digging equipment is used. Vibrating sieves or
screens that separate corms from cormels and allow the soil to pass through are
valuable in saving cormels as well as labor.
Modified potato diggers or specially designed corm diggers are used to harvest
large corms unless cormels are to be saved, in which case hand labor or the
sieves are used. Turning the corms out with a small plow or half sweep and
picking them up by hand reduces bruising and decreases the loss of cormels.
To prevent scorching by the summer sun, corms should be protected by plowing up
no more than can be picked up in 15 minutes and placed in the shade.
Harvesting, grading and cleaning operations cause small bruises and punctures,
unseen by naked eye, but which may result in corm rot. Slowly cured corms are
more susceptible to rotting. Captan applied as a dip or dust within a day
after harvest, controls those infections and protects corms later when they are
bruised in the cleaning and grading operations.
Curing and Grading
The cormels to be saved are separated, sieved and placed in shallow layers on
screen-bottom trays to cure at room temperatures. Corms, also, are placed in
similar trays to cure for two to three weeks, or at 85-100OF for 7 to 10 days.
Rapid or excessive loss of corm weight in curing is detrimental to corm vigor.
In cold weather, corms may be cured with forced, warm air but the relative
humidity of the air should be high enough to avoid much weight loss. After the
first hour, the temperature of forced air should be less than 800F (270C).
Warm-air curing allows cleaning of corms within 7 to 10 days after harvest.
Cleaning involves the removal of roots and mother corms. Large mother corms
are removed by twisting with hands, whereas small corms are cleaned by a de-
rooter machine with wringer-like, revolving steel or plastic bars. Corms are
then dusted or dipped in a fungicide. When dry, corms are sized with a grading
machine or by sieves:
Jumbo-size corms over 1 3/4 inch in diameter; over 14 cm in circumference.
No. 1 corms 1 1/2 to 1 3/4 inch in diameter; or 12-14 cm in circumference.
No. 2 corms 1 1/4 to 1 1/2 inch in diameter; or 10-12 cm in circumference.
No. 3 corms 1 to 1 1/4 inch in diameter; or 8-10 cm in circumference.
No. 4 corms 3/4 to 1 inch in diameter; or 6-8 cm in circumference.
No. 5 corms 1/2 to 3/4 inch in diameter; or 4-6 cm in circumference.
No. 6 corms 1/4 to 1/2 inch in diameter; or 2-4 cm in circumference.
Planting stocks are Numbers 4, 5, and 6 corms grown from cormels; and flowering
stocks for summer growing are No. 3 corms and larger. Corms to be sold are
counted by hand or by mechanical or electronic counters with an endless-belt
conveyor. The number of small corms is approximated by applying the average
weight per hundred to the total weight.
FUTURE OF CORM PRODUCTION
The future for gladiolus corm production is dependent on an active flower
market business. Markets should expand and improve flower outlets and better,
disease-tolerant cultivars are being produced in some countries and by one or
more commercial growers to serve the industry. Many commercial laboratories
offer custom tissue-culture service; this technique could be used for
outstanding cultivars that have a propagation or disease problem. Corm
production is a labor-intensive industry suitable for overseas development
because dormant corms can be shipped by slow, inexpensive transport to flower
producers. Selection of proper geographical areas for corm production can be
cost effective because storage facilities are minimal where corms are marketed
soon after the curing period. Cool storage for cormels and planting stock
corms requires a small space compared to the space needed for storage of the
The gladiolus industry in the future must take advantage of geographical
benefits, cost effective procedures, and look to advanced technology in
breeding, crop management, and marketing to stimulate quality production of
corms for the flower industry.
Special precautions should be taken in gladiolus culture because the plants
react differently than most crops to certain chemicals and practices:
1. Never place fertilizers, especially animal by-products, near or under
corms and cormels because organic products usually increase incidence
of corm rot and blemishes. Mineral fertilizers placed under corns or
cormels burn the roots.
2. The use of ammonium-nitrogen and urea tend to increase Fusarium
disease. Avoid acid soils, add lime for a pH of 6.5 to 7.0 and use
nitrate-nitrogen sources of fertilizer when soil is cool and wet.
3. Avoid planting gladiolus after a bean crop because of residual
Rhizoctonia solani, a common soil-borne fungal pathogen. Corn (maize)
is a good crop in rotation with gladiolus.
4. If gladiolus crops must be planted after gladiolus every year or two,
fumigate the soil or add DCNA and a nematicide as labeled.
5. Do not plant gladiolus in fields where atrazine herbicide was used in
the previous crop. Also avoid irrigation water from ponds where run-
off comes from atrazine-sprayed fields. Residues of simazine and ETPC
are also toxic to gladiolus.
6. Most copper fungicides used as spray or dust are toxic to gladiolus
leaves, especially in warm weather.
7. All fluorides are toxic to gladiolus leaves whether applied to leaves
or absorbed by roots from soil. The soil pH should be held above 5.8-
6.0. Do not spread superphosphates, which contain fluoride, when dust
may adhere to wet leaves, causing a severe tip burn.
8. Do not add sulfur to mixed fertilizer. Sulfur lowers pH making
fluoride more soluble.
9. Certain phosphatic insecticide granules placed in excess on corms or
cormels in open furrow cause "white tip" of leaves.
10. Test each new control measure on a small scale, before exposing the
entire crop to unknown potential damage.
11. Because climate, soils, cultivars, and cropping systems differ in
agricultural areas, it is expedient for growers to enlist the aid of
County Extension Service personnel to solve their corm production
12. Mention of a pesticide or chemical does not imply guarantee of
effectiveness or safety, nor that the chemicals or uses discussed have
been registered by appropriate State and Federal agencies.
13. WARNING: PESTICIDES ARE POISONOUS. Read and follow all directions and
safety precautions on labels. It is dangerous, wasteful and illegal to
do otherwise. Handle carefully and store in original labeled
containers, out of reach of children, pets and livestock. Dispose of
empty containers safely, and immediately according to label's
DISCLAIMER: It is the responsibility of each user to determine if the intended
use and/or tank mixes are within the law in the intended location, state or
country of use. Mention of a specific proprietary product does not constitute
an endorsement by the authors, the University of Florida, or the Cooperative
Extension Service. Individuals desiring information regarding currently
labeled pesticides for a crop are encouraged to contact Extension or other
knowledgeable personnel in their respective states. The user of information
printed in this paper assumes all risks for injury or damage to self, other
persons, animals, plants and property.
R. 0. Magie, Plant Pathologist, Emeritus; A. J. Overman, Professor and
Nematologist; J. P. Gilreath, Associate Professor and Weed Scientist; W. E.
Waters, Professor and Center Director; G. J. Wilfret, Professor and Geneticist;
J. F. Price, Associate Professor and Entomologist; and S. S. Woltz, Professor
and Plant Physiologist, respectively, Gulf Coast Research & Education Center,
University of Florida, IFAS, 5007 60th Street East, Bradenton, FL 34203.