Rain is expected this weekend. Watch for Botrytis, especially during cloudy and rainy weather. A wide variety of plants are susceptible and plants may be attacked at any stage of growth, especially new tender growth, freshly injured tissue, and senescing or dead tissue. Sometimes Botrytis will appear as a stem canker and is also very common on flowers. Botrytis cannot be effectivly controlled with fungicides alone. Cultural practices to reduce Botrytis include: Spacing plants to allow good air circulation and reducing humidity and leaf wetness to prevent spore germination.
Bacterial Leaf Spot disease has developed on certain varieties of Verbena. DonÃ¢â‚¬â„¢t confuse this disease with powdery mildew or with fungal leaf spot diseases .
Powdery mildew has become more common in the past few week on susceptible crops including gerbera daisy, vegetative petunias, viola, phlox and other favored hosts. Some varieties of verbena including Babylon Blue, Babylon Carpet Blue, Babylon Purple, Babylon Red, Babylon White, Sparkler Red White, Tukana Scarlet and Tukana White were also very susceptible to powdery mildew in a recent Michigan State Horticultural Demonstration Garden cultivar trial.
Thielaviopsis basicola has been seen on a number of crops this year including Calabrachoa, pansy, vinca (Catharanthus) and snapdragon. Plants in a tray will often be uneven in height and stunted plants tend to be lighter in color. Roots may be shriveled, brown to black and under-developed. The fungus thrives in cool weather and pH above 5.6. As temperatures warm up injury to the root system may slow down and plants may or may not recover. However, infected plants should be discarded.
Edema (oedema) is a physiological problem occurring primarily on ivy geraniums. It also occurs on sweet potato vine, begonias, and cole crop vegetables like cabbage and cauliflower. Edema is not a disease or virus and it is not transmittable from one plant to another.