Mycosphaerella blight is more problematic in cool and wet environments. If the disease starts to develop in the lower canopy in June, the disease can reach the destructive phase in July. Lower stem infection leads to excessive lodging, stem rot and yield reduction. From the standpoint of variety resistance, no discussion is necessary because none of the varieties have good tolerance to the disease. The best ratings on the scale are fair, which really doesn t amount to much.
Powdery mildew is an unusual disease because it is favored by dry conditions.
For example, it regularly shows up in the winter nursery in Arizona, where it virtually never rains. Powdery mildew is always a bigger problem in dry climatic cycles. Dew and moisture in the lower canopy followed by warm sunny days cause the disease to develop very rapidly in July. The earlier the disease shows up, the higher the potential for economic loss. Good resistance is available, but few breeders have used it so far.