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There are two flower and bud rots of carnations: Botrytis flower blight and Fusarium bud rot. 
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SYMPTOMS: Petals of flowers affected with Botrytis turn brown either while in bud or after the flower 
opens. Frequently a number of petals may be matted together by the growth of the fungus and if 
the weather remains warm and moist the affected petals soon become covered with the brownish- 
gray growth of the organism. This brownish-gray growth is covered with a powdery mass of spores. 
Botrytis flower blight occurs only during periods of extremely high humidity and the Botrytis spores 
are produced in large numbers when the atmosphere is warm and damp. Such conditions provide 
an ideal environment for the germination of the spores and growth of the organism. If the weather 
becomes dry the fungus does not develop further and the affected parts become brown, dry and 
brittle. This organism does not affect other parts of the carnation although it may affect many other 
kinds of plants. The spores are numerous and are readily disseminated by slight air currents, 
CONTROL: The only proven control for this disease is proper use of heat and ventilation. Heat should 
be started in the houses an hour or two before sundown and if the vents are left open a bit so that 
the moisture-laden air can move out, there will be little trouble experienced with Botrytis blight. 
Northland is a very susceptible variety and it has been suggested to plant this variety in a south 
bench or in houses which have the best ventilation. 
SYMPTOMS: The symptoms of Fusarium bud rot are quite different from those of Botrytis in that young 
buds may appear outwardly normal, but when opened they show a moist, brownish, decayed mass 
of the inner floral organs. These tissues may be rotted through by the Fusarium which is generally 
visible as a white cottony growth. Large white fat mites are also present in this tissue. White vari- 
eties of carnations are more susceptible than colored varieties. 
This disease has a very interesting relationship. The fungus itself produces a disease on various com- 
mon grasses known as silver top and these infected grasses are the source of the carnation disease. 
However, for infection to take place in carnations, a mite Pediculopsis gramimium, is necessary. This 
mite carries the fungus into the carnation buds and wounds the tissue so that the fungus can enter 
the tissue. Then the mite feeds on the fungus as it grows. Thus, there is a sort of symbiotic rela- 
tionship between the disease organism and the insect. The mite is necessary to dissemination and 
infection by the organism and the growing organism is necessary for the subsistence of the organism. 
CONTROL: Picking off the infected buds as soon as they are detected plus a good insect control practice 
in the greenhouse will check the spread of this disease. 
Botrytis flower blight on Northland. 
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