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Copyright 2005, Board of Trustees, University
Mimeographed Report 60-1 November, 1959
University of Florida
Sub-Tropical Experiment Station
CONTROL OF LEAF AND FLOWER DISEASES OF CHRYSANTHEMUM
Lorne A. McFadden
Florists' chrysanthemums are subject to several leaf and flower diseases in
Florida. Those occurring on the flowers include Botrytis petal spot, Ascochyta ray
blight and ray speck while bacterial leaf spot, Ascochyta leaf blight, Septoria
leaf spot, foliar nematode and yellow strapleaf disease occur on leaves of
The purpose of this report is to discuss the control of three of these diseases;
namely, Botrytis petal spot, Ascochyta ray blight and bacterial leaf spot. Foliar
nematode of chrysanthemums has been observed only on rare occasions in commercial
plantings. Growers using insecticides such as parathion have not experienced
losses due to foliar nematode. Septoria leaf spot, although an important disease
of chrysanthemums in Florida, has not been difficult to control when plants are
sprayed regularly with a good fungicide. Ray speck, caused by a Stemphyllium fungus
has been observed on a few occasions. but its distribution appears limited. The
yellow strapleaf disease is of recent occurrence and its cause and control are
under investigation at the Gulf Coast Experiment Station.
The Ascochyta fungus attacks chrysanthemum flowers usually on one side causing
a tan to dark brown rot. The fungus grows into the peduncle causing it to urn -,
dark brown to black. Unless controlled, the fungus can cause almost tp ; loss of :
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flowers either in the field or during shipment to wholesale markets. The ray
blight fungus also causes irregular brown to dark brown lesions or blotches on
leaves and stems of chrysanthemums in Florida. Under optimum conditions, such as
frequent rains, fungus spores are spread to adjacent plants.
Botrytis petal spot is evident as small spots varying in color (pinkish,
purplish, brownish), depending on the variety of chrysanthemum attacked. Under
optimum conditions the spots become numerous resulting in reduction of flower
quality and appearance.
A "new" bacterial leaf spot was observed during the fall of 1957 causing almost
total loss of stock plantings of Bluechip chrysanthemums. The disease appears
during the rainy seasons of the spring, summer and fall months. The spots first
appear on the lower,.mature leaves but under continued wet weather conditions may
reach the top of plants at time of flowering. The spots are dark brown to black
with lighter tan centers. At times, numerous spots coalesce to form large, necrotic
areas on the leaf. A careful examination of spots when dry show characteristic
concentric rings or target patterns. There is no yellowing around the spots as in
the case of Septoria leaf spot.
Experiments carried out at the Sub-Tropical Experiment Station over the past
2 years indicate that all three diseases can be controlled by using frequent
applications of protective fungicides in conjunction with a strict program of
sanitation around the nursery.
The fungicide tests were carried out in outdoor replicated plots provided with
overhead irrigation and lights. Sprays were applied twice weekly regardless of
weather conditions, using a 12 gallon Myers Baronet sprayer at 200 pounds pressure.
- 3 -
To assure optimum disease development the flowers of Whitetop chrysanthemums were
artificially inoculated with the Ascochyta fungus while flowers of Bluechip
chrysanthemums were inoculated with the Botrytis fungus. Overhead irrigation at
frequent intervals provided optimum conditions for infection. No attempts were made
to inoculate the Bluechip and Iceberg plants with the bacterial leaf spot pathogen
although frequent use of overhead irrigation made conditions suitable for disease
The results of the tests against Ascochyta ray blight and Botrytis petal spot
are summarized in Table 1. Over a 2 year period most of the commercially available
fungicides have been tested against these diseases. A number of materials proved
unsatisfactory either due to lack of disease control or phytotoxicity. Ascochyta
was best controlled with spray applications of maneb, maneb + captain, captain, zineb
and zineb + captain. Botrytis was best controlled using sprays of maneb, maneb +
captain, zineb and zineb + captain. No injury resulted using these materials on open
flowers of Bluechip and Whitetop chrysanthemums.
The data on bacterial leaf spot control (Table 2) shows tribasic copper sulfate
and Agri-mycin 500 superior to Agri-mycin 100 and Agri-Strep. Slight yellowing of
foliage occurred in plants receiving Agri-mycin 100 and Agri-Strep and to a less
extent with Agri-mycin 500, but phytotoxicity was not severe even after repeated
applications. Flowers of Bluechip and Iceberg chrysanthemums were not injured by
the above mentioned materials.
Table 1. A summary of tests carried out over a 2 year period to control Botrytis
petal spot and Ascochyta ray blight of chrysanthemums.
Concentration Disease Control
Materials per 100 gallons or ppm Ascochyta Botrytis Plant Safety
CM-19 + captain
Maneb + captain
Zineb + captain
Phytoactin + captain
Tribasic Copper sulfate (53a)
Concentration reduced to
1 1/2 ppm
1 1/2 Ibs.
1 pt. + 3/4 lb.
1/2 lb. + 3/4 lb.
1/2 lb. + 3/4 lb.
1 1/2 Ibs.
1/2 qt. + 3/4 lb.
1 1/2 lbs.
150 ppm but due to severe injury
all plants died.
- 5 -
Table 2. Results of tests to control bacterial blight of chrysanthemums.
Treatment Concentration Disease Control Plant Safety
Tribasic Copper sulfate (53%) 4 lbs. 100 gals. 70% Safe
Agri-mycin 500* 3 lbs. 100 gals. 60 Fairly safe
Agri-mycin 100** 60 ppm 50 Fairly safe
Agri-Strep*** 60 ppm 47 Fairly safe
Control (water sprayed) 0
Streptomycin 15.01, Terramycin 0.5% Chas. Pfizer & Co.
** Streptomycin sulfate 37% Merck & Co.
*** Streptomycin 1.75ao, Terramycin 0.18o%, tri-basic copper sulfate 42.4o -
Chas. Pfizer & Co.
CAUTION: Materials containing streptomycin can cause foliar yellowing, stunting and
hardening of chrysanthemums if used at concentrations in excess of those
Recommendations.--The data presented show maneb, zineb and captain to be
effective in controlling both Ascochyta and Botrytis. Although maneb at 1 lb. -
100 gallons is highly effective against both diseases, preference is given to maneb
1/2 Ib + captain 3/4 lb. per 100 gallons since it is less likely to cause injury to
open flowers and it leaves less objectionable residues. Zineb at 1 lb. or zineb
1/2 lb. + captain 3/4 lb. per 100 gallons also gives good disease control. Sprays
should be applied a minimum of once weekly on vegetative growth and twice weekly
(more frequently during rainy periods) on open blooms. To avoid possible spray
injury plants should dry quickly following fungicide application. Ascochyta must
also be controlled during vegetative growth and the use of the same fungicides is
Bacterial leaf spot may be controlled using either tribasic copper sulfate
at 4 lbs. 100 gallons or Agri-mycin 500 at 3 Ibs. per 100 gallons. Sprays should
be applied weekly to susceptible varieties (Bluechip, Iceberg, etc.) particularly
during periods of frequent and heavy rains. Stock plantings should also be sprayed
weekly for best results.
In addition to employing the most effective materials, thorough spray coverage
of plants is necessary for maximum control.