Greenhouse Update - September 1, 2006
Leanne Pundt, Extension Educator, University of Connecticut
Fungus gnat feeding damage on poinsettias - Check roots to see that they are white and healthy with no signs feeding damage. Blunt root tips, strands or nibbled roots can be an sign of fungus gnat feeding. It’s important to develop a healthy root system early in the production cycle, and fungus gnat feeding can definitely check the root's systems growth. Many different insect growth regulators such as Distance (follow label safety precautions regarding treatments on poinsettia carefully), Citation, Enstar, Azatin, Ornazin, and Aza-Direct may be options for use against fungus gnat larvae. Gnatrol, BT, can be used against the small, first instar larvae. If fungus gnats are breeding on the floor, treat floors as well. After treatment, place potato slices on the media surface, for 48 hours to check for the absence of the black-headed larvae.
Powdery mildew – humid conditions have lead to powdery mildew on various crops including beebalm, veronica, peony, sedum etc. Most growers are familiar with the white, talcum powder like growth on the upper leaf surface that is characteristic of powdery mildew. Regular scouting is needed for detection because infections can begin on the lower leaf surfaces that are easily overlooked.
On some plants, infected leaves turn a purplish color. On sedum, brown scab-like lesions develop with little powdery growth. From a distance, powdery mildew could be easily confused with a leaf spot disease. Look closely for the fine, white fungal threads and chains of powdery mildew spores.
Leaf mold on greenhouse tomatoes - can occur during humid conditions in the spring and fall. Symptoms begin with small, yellow spots on the upper leaf surface. The fungus (Fulva) sporulates on the lower leaf surface with olive-green to grayish-purple velvety growth (See photo). Like Botrytis blight, this disease is best controlled by good environmental management. Keep humidity below 93% by heating and venting and avoid wetting the foliage when drying is slow. After harvest, carefully remove and destroy all plant debris.
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