Title: Onion production guide for commercial growers
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Permanent Link: http://ufdc.ufl.edu/UF00084290/00001
 Material Information
Title: Onion production guide for commercial growers
Series Title: Onion production guide for commercial growers
Physical Description: Book
Creator: William, R. D.
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
 Record Information
Bibliographic ID: UF00084290
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 51242770

Full Text

July 1977 Ci.rcular 176D
S ev)leon of no.


Florida Cooperative Extensioneice
Institute of Food and Agricultural Sciens /
University of Florida, Gainesville
John T. Woeste, Dean for Extension


Bulbing Types
Onions can be grown on most soils found
Florida. Excellent yields can be obtained wi
the newer varieties and hybrids. For best wat
control, onions should be grown on raised bed
Uncertainty of dry weather at harvest time f
field curing of the bulbs is a major factor limiti
commercial production of onions in Florida. Art
ficial curing of the bulbs can be accomplished b
using drying equipment. Generally, under Florid
conditions, onions grown on organic soils do n
cure and keep as well as onions grown on sand

The varieties described below will grow under
the short daylight conditions of winter and bul
in the spring with increasing day length. Plan
only short day varieties recommended for th
Eclipse-Highly resistant to the disease pin
root, medium size, thick-flat shaped and whit
Excel-Highly resistant to the disease pink
root, medium size, thick-flat shaped and amber
Texas Grano 502-Large size, top-shaped, and
yellow skinned.
Ringer-Similar to Texas Grano 502, but has
a higher percentage of single centers and is
slightly more spindle shaped. Highly resistant
to the disease pink root.
Granex-Hybrid, highly resistant to the disease
pink root, and thick-flat to globe shaped. Both
yellow and white skinned types available.
Tropicana (red)-Resistant to the disease pur-
ple blotch, thick-flat shaped, and red skinned.
Pungent. Stores well.
Laredo-Highly resistant to the disease pink
root, globe shaped and yellow skinned. (For

Red Creole C-5-Resistant to the disease purple
blotch, small, thick-flat shaped and red skinned.
Very pungent. Stores well. (For trial.)

Planting Dates
Seeding Dates
For transplant production beds Sept. 15 to Nov. 15
For direct field seeding Oct. to Nov.
Transplanting Dates1 Dec. 15 to Jan. 15
Harvest Dates2
From transplanting Apr. to June
From direct field seeding Apr. to June
1 Onion transplants should be "pencil-size" and vigorously
growing. To facilitate handling, transplant tops can be
pruned slightly 5 to 7 days before transplanting.
2 See section on Harvesting and Curing.

Planting Distances and Seed Rates
Between Seed Rates
Rows1 Within Rows
Transplant Production
Bed 12 to 24" 70 to 140 seed/ft.
Approx. 20 Ibs. seed/ac.2
Field Production Bed
From transplants 12 to 24" 6 to 12 plants/ft.
From direct seeding 12 to 24" 12 to 16 seeds/ft.
3 to 4 lbs. seed/ac.
1 Single rows may be spaced 12 to 24" apart or multiple
rows may be planted as close as 6" on top of a bed if
weeds can be controlled without cultivation.
2 Approximately 2 lbs. of seed will be required to produce
enough plants for one acre.

Mineral soils used for the production of trans-
plants should be fertilized with 800 to 1,000
pounds of 8-8-8 per acre. If an organic soil is
utilized, a 0-8-8 material can be substituted. The
fertilizer should be mixed into the upper 2 inches
of soil about 10 days before seeding. After seed-
ing, the soil should remain moist.
Recommended rates of fertilizer for field pro-
duction of onions on different soil types are pre-
sented in the following table.

Onion Fertilization for Different Soil Types
Basic Supplemental
Soil Application Applications
Types N-P205-K20 N-P205-K20
Actual lbs./acre
Irrigated 120- 120- 120 15 - 30
Non-irrigated 96- 96- 96 15-0-30
Peat Muck1 0-120-120 0- 0- 0
Marl 54- 72- 72 15-0-30
1 These fertilizer rates are suggested for onion production
on organic soils low in P20, and KO. Where soil test
show a medium level of P205 in an organic soil, reduce
the suggested amount of P20, by one-third; and where
soil P205 levels are high, reduce by two-thirds. Follow
the same suggestions for medium and high levels of

The basic application of fertilizer may be ap-
plied as a single dose prior to planting or as split
applications with 1/ to 1/2 applied prior to plant-
ing and the remainder may be sidedressed in 1 to
3 applications. Split applications reduce soluble
salt problems and fertilizer loss due to leaching.
The amounts of fertilizer suggested in the previ-
ous table are sufficient to grow an onion crop
under normal conditions. Before bulbing, onions
will respond to supplemental applications of ni-
trate nitrogen during periods of cool weather or
following heavy rainfall.
Micronutrients--A general guide for supplying
adequate levels of micronutrients (minor ele-
ments) in the absence of past experience or soil
tests is to add 0.3% MnO, 0.2% CuO, 0.3% Fe2O3,
0.2% ZnO, and 0.2% B2O, to the fertilizer mix-
ture. The micronutrients can be obtained from
mixtures of oxides, sulfates, chelates or fritted
materials. Growers should consider the micronu-
trients applied in fungicides in the overall man-
agement of a fertilizer program.
On muck and peat soils, higher rates are neces-
sary to overcome the tendency of micronutrients
to be completed or tied-up by the organic matter
in these soils.

Pesticide Precautions
Read the label on each pesticide container be-
fore each use. Heed all cautions and warnings.
Store pesticides in original labelled containers, in
a safe place, and preferably under lock and key.
Promptly and safely dispose of empty containers.
Information is given on recommended pesticides
and minimum days between last application and
harvest. There will be changes and cancellations;
therefore, the grower must keep abreast of de-
velopments through county extension agents, ex-
periment stations, industry, etc.

Insect Control
Insecticide and Amount Per Days to
Insect Formulation' Acre Harvest
Thrips2 Diazinon 4E 1.0 pint 10
Malathion 5E 1.5 pint 3
Parathion 4E 0.5 pint 15
Mevinphos 2E
(phosdrin) 1.0 quart 1
Leaf Miners Diazinon 4E 1.0 pint 10
Parathion 4E 1.0 pint 15
1 Other formulations may be registered 'and available.
2 Apply insecticide when thrips appear and repeat when
necessary. Direct nozzles over rows close to plants,
spraying down into the leaf sheaths. Addition of a
spreader-sticker in the spray solution is suggested.

Cutworms-If cutworms are known to be
present, a preplant application of 2 pounds of tox-
aphene active ingredient per acre can be used. The
soil should not be disturbed for 3 to 5 days after
application. If cutworms become a problem after
planting the onions, a bait such as 2.5 to 5%
toxaphene can be distributed at the rate of 20 to
40 pounds per acre near the base of the onion
Wireworms-On mineral soils, 2 pounds active
ingredient per acre of parathion or diazinon
can be applied as a preplant soil application. On
muck and peat soils, apply parathion at 5 pounds
or diazinon at 4 pounds active ingredient per acre.
Distribute these materials evenly over the soil

surface and incorporate immediately into the u
per 6 inches of soil, 2 to 3 weeks before planting
Mole Crickets-If the insects are known to bg
present, a preplant spray, dust, or granular ap
plication of diazinon (2 pounds active ingredient
per acre) can be used about a week prior to plant
ing. A preplant bait of 2.5 to 5% toxaphene at th
rate of 20 to 40 pounds of bait per acre can als
be used. After planting the crop, control is limited
to the use of a bait at the rates given above.
Avoid application of toxaphene bait directly to
the onion foliage.

Nematode Control
Onions are severely affected by sting, stubby-
root, root-knot, and awl nematodes. Stubby-root
nematodes frequently build-up rapidly following
fumigation with D-D or Telone and cause injury
to direct seeded onions. Where the stubby-root
nematode occurs, fumigate and plant sets or
transplants. Because onions are sensitive to bro-
mine, a fumigant which does not contain bromine
should be used.

Nematicides-Rates and Use
Rates1 2 Fluid Oz./Chisel
Nematicide Gallons/Acre Per 1000 Linear Feet
D-D 20-25 59-73
Telone II 12-15 35-44
1 The overall rate per acre of fumigants is based on a
12-inch chisel spacing. If wide spaced rows (approxi-
mately 36 inches) are desired, the application rate of
D-D should be 79 to 97 fluid oz./chisel per 1000 linear
ft. and Telone II 46 to 62 fluid oz./chisel per 1000 linear
2 For organic (peat and muck) soils, rates should be in-
creased 75-100%.

Disease Control
Damping off and pink root in transplant beds-
Prevent infection of onion transplants by fumi-
gating the soil with a multipurpose soil fumigant
such as Vorlex or Vapam. Because these fumi-
gants require special application techniques and
are multipurpose pesticides, consult the label and
follow directions carefully.

Seed treatments with a fungicide such as thiram
or captain and rotation of seedbeds will reduce
infection of transplants. Also, planting of re-
sistant or tolerant varieties to such diseases as
pink root are effective control measures.
Root rot and other soil borne diseases in field
production beds-Always plant disease-free seed
and transplants in the field. Adequate crop rota-
tion and nematode control will also reduce in-
fections of soil borne diseases.

Foliar Diseases
Minimum Days
Diseases Fungicide Lbs./100 Gallons* To Harvest
Mildew, Maneb, or 1% to 2 lbs. NONE
and Zineb, or 2 lbs. **

Purple Dithane M-45,
Blotch or 1% to 2 lbs. 7***
Manzate 200 1% to 2 lbs. 7***
*Add a spreader-sticker to spray mix.
**No time limit on dry onions, 7 days on green onions.
***Do not apply to exposed bulbs.

Newly emerging seedlings are susceptible to
damage from windblown particles, especially sand.
To prevent stand reductions and the need to re-
seed or replant the acreage, windbreaks should be
established for protection of the seedlings. Where
windbreaks are not utilized for protection, a light
overhead irrigation to wet the soil surface can
prevent sandblasting.

Onions are a shallow rooted crop. An adequate
supply of moisture is needed to maintain uniform
plant growth throughout the growing period. Non-
uniform growth due to lack of moisture often can
result in reduced yields and the increased occur-
rence of doubles or splits thus resulting in a reduc-
tion in quality. When the plants begin to mature,
irrigation should be reduced. Excessive irrigation
at this time may induce regrowth or sprouting

of new roots which can hinder proper curing and
storage following harvest.

Weed Control
Onions can be seriously affected by competition
with weeds for soil moisture and nutrients. Deep
cultivation can cut and injure roots, thereby re-
ducing growth and yield. Therefore, shallow culti-
vation practices are recommended. When bulbing
begins, cultivation should cease. Chemical methods
of controlling weeds result in reduced weed com-
petition and less "trash" at harvest.

Herbicides-Rates and Use
Lbs. Active
Time of Ingredient/A
Time of
Application Sandy Organic
Herbicides To Crop Soils Soils
CDAA (Randox) Preemergence 4 to 6
Postemergence2 4 to 6
Chlorpropham Preemergence 6+ 6
(Furloe) Preemergence 3 to 4 6 to 8
DCPA (Dacthal) Preemergence 10.5 -
Posttransplanting 10.5 -
Chlorpropham Preemergence 6+1 -
Chlorpropham3 Posttransplanting 6+1 -
(Tenoran, Norex) Postemergence 3 to 4
Nitrofen3 (Tok) Postemergence 3 to 4
SApply as directed spray to base of plants at second
true leaf stage. DO NOT USE ON GREEN BUNCH-
ING ONIONS. CDAA is more effective against annual
grasses than broadleaf weeds.
2May be applied postemergence before weed emergence.
3 For trial use only. Consult the label for specific appli-
cation directions and precautions.

Physiological Disorders
Bolting-The switch from the vegetative to the
reproductive state of growth in onions can be
recognized by the formation of a seedstalk (known
as bolting) and is induced by exposure to cool or
freezing temperatures. As a general rule of
thumb, bolting is greatest when onions are ex-
posed to a late warm fall followed by a cool spring,

whereas a cool fall and a mild spring result in the
least amount of bolting. The size of the trans-
plants or sets used, as well as temperature and
variety, influences the amount of bolting. General-
ly, the larger the size of transplants or sets, the
higher the incidence of bolting.
Splitting-Non-uniform growth during the
bulbing stages, usually due to poor soil moisture
control, alternating periods of cool spring weather,
or excessive nitrogen levels at time of bulbing
can often result in increased numbers of split
bulbs. Varietal selection and careful management
of soil moisture and nitrogen will help reduce
Sprouting-A chemical treatment of 2 pounds
of maleic hydrazide active ingredient per acre ap-
plied to green foliage 10 to 14 days before harvest
retards high respiration and sprouting in storage.

Harvesting and Curing
Onion bulbs continue to enlarge after the tops
fall over late in the season. To facilitate rapid
and uniform curing, the tops can be "rolled" down
using a lightweight roller when 10% of the tops
have fallen naturally. Approximately 7 to 10 days
before harvest, the onions may be undercut and
lifted slightly without removing them from the
row. These practices facilitate the curing process
by reducing water uptake and growth.
At harvest, the onions may be windrowed and
left in the field to dry, if weather permits. Other-
wise, the bulbs may be topped and placed in shal-
low crates under a roof to dry, or mechanical
drying is possible where heated air is circulated
through large pallet boxes in a closed structure.
The onions can be cured in 48 hours at tempera-
tures not exceeding 1100F, provided there is good
circulation of the heated air.
Experimentally, onions have been cured with
the use of solar radiation inside a clear or black
plastic tunnel. After normal harvesting and han-
dling, the onions are placed in slated crates inside
the plastic tunnel where a dry environment can
be maintained. Air movement is enhanced by
leaving the tunnel ends open and placing a chim-
ney in the middle of the tunnel. However, drying

time may be considerably longer than the me-
chanical forced drying described above.

Discard all diseased, injured, and "bottle-
necked" bulbs prior to storage. Store only well
cured bulbs that exhibit "tight" necks and dry
outer scales, or loss due to rotting will be high.
Storage temperatures should be 320F with 65-
70% relative humidity. Most mild onions grown
in Florida usually cannot be stored safely for ex-
tended periods of time.

Green Bunching Types
Green bunching onions can be grown from
"sets" or seeds. Sets are onion bulbs measuring
1/2 to 3/4 inch in diameter. Onion sets should be
sized at planting time to improve uniformity of
maturation and size at harvest. Under good grow-
ing conditions, the bulbs produce marketable
bunching onions about 45 to 60 days after plant-
ing. Green bunching onions can also be grown
from seed, but to produce a saleable onion by this
method requires 75 to 90 days. Sets can be used
for green bunching onions for late fall and early
winter marketing. Seed can be used for later

Not all varieties are available in both sets and
seeds. A good source of sets is often difficult
to find. When a grower finds a satisfactory source,
it should be maintained. Nearly all the varieties
utilized for bulbing onions can be direct seeded
and used for green bunching onions. However,
there are non-bulbing varieties that have been
selected specifically for green bunching onions.
Bulb forming types used prior to bulb forma-
tion for bunching onions:
Varieties used most often from sets:
White Portugal or Silverskin
Varieties most often direct seeded:
Perfecto Blanco

White Lisbon
Crystal White Wax
Non-bulbing types, usually produce clumps
which are divided and used as bunching onions:
Evergreen Bunching
Japanese Bunching

Planting Dates
North Fla. Central Fla. South Fla.
Seeding Dates
from sets Aug.-Mar. Sep.-Feb. Sep.-Feb.
Production from
field seeding Dec.-Apr. Jan.-Mar. Jan.-Mar.
Harvest Dates
From sets Oct.-Jan. Nov.-May Nov.-May
For direct
field seeding Mar.-Jun. Apr.-Jun. Apr.-Jun.

Planting Distances and Seed Rates
Planting Between Seed Rates
Depths Rows Within Rows
For sets 2 to 4" 12 to 24" 4 to 6 sets/ft.
8 to 12 bushels/ac.
For Direct
Field seeding 1 to 2" 12 to 24" 20 to 56 seeds/ft.
6 to 8 lbs. seed/ac.
I Single rows may be spaced 12 to 24" apart or multiple
rows may be planted as close as 6" on top of a bed if
weeds can be controlled without cultivation.

Same as for bulbingg" types.

Pest Control
Same as for bulbingg" types, except where

Green bunching onions are perishable and
should not be stored more than a few days. The
storage conditions should be 320F and 90-95%
relative humidity. Exposure to high temperatures
will result in yellowing and decay of the tops.

Additional Literature
1. Florida Extension Circular 193, "Commercial
Vegetable, Insect, and Disease Control Guide."
2. Florida Extension Circular 196, "Chemical
Weed Control for Florida Vegetable Crops."
3. Florida Extension Circular 225, "Commercial
Vegetable Fertilization Guide."
4. Florida Extension Circular 153, "Commercial
Vegetable Variety Guide.'"
Because extension circulars are revised periodi-
cally, be sure to obtain latest editions.

Prepared by: R. D. William and James Montelaro.

Acknowledgements: The authors wish to express their
sincere thanks to D. S. Burgis, L. H. Halsey, D. D. Gull,
V. L. Guzman, N. C. Hayslip and other faculty members
of the Institute of Food and Agricultural Sciences who
made helpful suggestions in the preparation of this pro-
duction guide.

Special contributions were made by:
F. A. Johnson and J. E. Brogdon-Insect Control
T. A. Kucharek-Disease control
R. A. Dunn-Nematode control

The use of trade names in this publication is solely for
the purpose of providing specific information. It is not a
guarantee or warranty of the products named and does
not signify that they are recommended to the exclusion of
others of suitable composition.



This public document was printed at an annual cost of
$461.80 or 15.4 cents per copy to inform county exten-
sion directors, industry representatives and vegetable

Single copies are free to residents of Florida and may be obtained
from the County Extension Office. Bulk rates are available upon
request. Please submit details of the request to C.M. Hinton, Publi-
cation Distribution Center, IFAS Building 664, University of
Florida, Gainesville, Florida 32611.

(Acts of May 8 and June 30, 1914)
Cooperative Extension Service, IFAS, University of Florida
and United States Department of Agriculture, Cooperating
K. R. Tefertiller, Director


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