Gulf Coast Station Mimeo Report No. 58-1
Chrysanthemum Research Results 1957
R. O. Magie
Diseases of leaves and flowers were difficult to control during
the past winter and spring because of frequent fogs and rains. The loss-
es sustained by some growers were caused by 1) Insufficient spray coverage,
2) Poor sanitation, or 3) Reduction of flower quality by too much spray
residue. That some growers were practically free of disease losses indi-
cates that the spray programs were effective when properly carried out.
On some farms, however, prolonged fogs and rainy weather interfered with
the regular spray schedule.
Botrytis disease is present in most plantings from the time the
cuttings are planted. The lower, shaded leaves are more susceptible to
infection, although the upper leaves may be attacked in prolonged wet weath-
er. The spots are dark brown, usually large and located at the edge of
the leaf. Leaf infection is usually of no importance of itself. Spore
production is so prolific, however, that a small percentage of infected
leaves may spread the infection to the flowers. Botrytis infection not
only ruins the flowers before cutting but may develop in transit to mar-
ket, ruining a shipment that looked healthy when packed.
Some white pompon varieties are very susceptible to Botrytis.
Diseased petals are light brown at first, darkening with age. Petal tips
may be attacked butmostly the base of petals and the calyx (small green
"petals" at the base of flower) become diseased. Several petals in a
group are often killed by an infection at their base. Botrytis infec-
tion is identified by the gray mold or fuzzy spore growth on petals and
larger leaf spots. This growth tends to turn white on the shaded dead
Control of Botrytis. -- Sanitary practices are helpful if close-
ly supervised. Remove all brown leaves before the cuttings are planted
and again about ten days later. Spray plants with ferbam just before or
after handling the diseased leaves and avoid touching the plants when they
are wet. Destroy the brown leaves and wash hands frequently in denatured
alcohol or in a captan suspension, one quarter pound in 2 gallons.
Until the flowers begin to show color, spray every 5 to 12 days,
depending on the weather, using two pounds of ferbam to 100 gallons of
water. Spray the flowers with one pound zineb per 100 gallons plus one
and one-half ounces of a wetting agent such as Triton X-100. Spray the
flowers one to four times each week, the frequency depending on the weath-
er. Flowers of resistant varieties do not need to be sprayed as often as
the more susceptible varieties.
How to Spray. -- Spray the leaves mostly from below, but the
flowers should be sprayed mostly from above because the spores fall into
the top of the flowers and are carried to the base of the petals by dew
and rain. Frequent spraying over the tops of the flowers is more effec-
tive than very thorough spraying at longer intervals because flowers ar X
continually opening unprotected tissue to possible infection.
Frequently the flowers retain some water at the base of'Z e
petals between wetting periods. At such times, spray the flower i er
other day even though they must be sprayed when wet. Use only z JI 1
plus a wetting agent when spraying flowers that are not thoroughly ied
Ascochyta Ray Blight
This disease has caused some.heavy losses on the East Coast.
The fungus lives in the dried-up stems, leaves and flowers for several
years. Spores produced in leaf spots or other plant parts spread the ,
infection to the ray flowers, causing tan-brown to black rot of the bud,
stem and petals. Infection of flowers is often one-sided. If the dis-
ease is visible on some of the flowers before cutting, more of the flowers
will usually be diseased on arrival at the market.
Sanitation is important in controlling ray blight. Diseased
plant parts should be buried deeply or burned. Clean up the packing
house, sheds and fields between seasons and be sure that all trash piles
and refuse are buried or burned. Plow under or burn over neighboring
fields and ditches where diseased leaves may have been blown or carried
last season. Make it a practice to turn under the stubble as soon as a
bed is cut out.
Spraying. -- Our experience indicates that zineb controls ray
blight better than Botrytis disease. There would be less trouble in con-
trolling either disease if spore production were held down by sanitation
and proper spraying of the leaves before flowering.
The spray schedule suggested for Botrytis control is recommended
also for ray blight, except that using zineb alternated with ferbam would
be more effective on the leaves than using only ferbam. Both zineb and
ferbam could be used at 1 1/2 100 when alternated.
The usefulness of other spray materials such as maneb, captain,
Phygon and Thylate have not been evaluated. A spray test is planned for
It is common to find isolated plants with a stem rot that kills
or stunts the growth. Sometimes the disease spreads from plant to plant.
The common causes of stem rot are Rhizoctonia (Rhizoc) and Pythium fungi
which are found in practically all untreated soils. Rhizoc-infected plants
are stunted and the rotted stems are brown. Infected plants usually die
slowly. Generally only young plants are attacked by Rhizoc.
The Pythium disease occurs during wet weather and progresses
rapidly, killing the plants so quickly that they show no stunting. When
the stems are attacked on one side the plants may recover and produce
flowers. The outside of affected stems and leaf petioles are black to
dark brown in color. Pythium spores are carried into the treated beds by
surface water and splashing during heavy rains. It is doubtful that either
Rhizoc or Pythium fungi are spread much by the wind.
Control. -- Sanitation is very important in controlling the stem
rot diseases. Practical measures should be taken to reduce the chances of
contaminating treated beds with muddy shoes and tools. The planting area
should be protected from surrounding surface water by dikes and good drain-
age. A small dike can be thrown up just outside the shade or along the upper
side of the planting. If surface water is used for overheadd irrigation,
it would be advisable to filter it through sand in order to remove Pythium
Remove and destroy affected plants promptly. Avoid scattering
soil from the diseased plants and wash hands before handling healthy
plants. After removing diseased plants, drench the surrounding soil and
neighboring plants with a fungicide. For controlling Rhizoctonia, New
York State pathologists recommend a Terraclor (75% pentachloronitroben-
zene) drench, one pound in 100 gallons per 400 square feet of bed area
or three pounds of 20% Terraclor dust on the same area. Against Pythium
the following drenches are suggested for trial (the quantities given are
to be applied to 400 square feet of bed): 1) Thylate or Arasan SF-X at
one pound in 100 gallons, 2) Pano-drench "4" at 5 ounces in 100 gal.,
3) Panogen "15" at one ounce in 85 gallons, or 4) captain at three pounds
in 100 gallons.