Downy mildew is very prevalent on cucumbers, summer and winter squash throughout PA. Downy mildew generally shows as angular pale green to yellow areas bound by leaf margins on the upper surface of the leaves. When conditions are wet and humid greyish spores are visible on the underside of the leaf.
Downy mildew on cucumber. Upper leaf surface.
Powdery mildew In contrast powdery mildew discolors leaves with white powdery spores on both upper and lower leaf surfaces. Downy mildew does not overwinter in PA. It blows in on the air currents, generally from the South.
Early blight and Septoria are aggressively moving up tomato plants. Both diseases start on the lower leaves of plants. Early blight causes circular spots with a target appearance of concentric rings. Leaves develop yellow blighted areas and later the fruit may rot on the stem end. Septoria causes a peppering of lower leaves with circular spots. In wet conditions such as those of recent weeks rapid defoliation can occur. Three year crop rotation, mulching to prevent splashing, and proper staking and suckering to increase leaf drying are important cultural controls. Infected, seeds, stakes or soil can bring in the disease. For organic growers copper products showed one good and one poor result in recent studies. Conventional growers should rotate a chlorothalonil or mancozeb product with a systemic such as Tanos.
Conditions have been favorable for late blight which is spreading throughout the state. Late blight can quickly defoliate tomato and potato plants. The pathogen does no overwinter in PA without living tissue (ie cull potatoes) and generally comes in from Southern States on long distance wind currents. To track when late blight is in your area visit usablight.org. Practices that keep leaves dry as much as possible such as good staking/trellising and drip irrigation are important. For organic growers copper products showed one good and one poor result in recent studies. Conventional growers should rotate a chlorothalonil or mancozeb product with a systemic such as Tanos.
We are seeing significant bacterial spot on peppers. Lesions begin as water soaked spots that become brown and have an irregular shape. Infected leaves turn yellow and eventually drop off. The most important controls are preventative. Plant disease free seed. Stakes, cages and transplant trays should be new or disinfected. Sodium hypochlorite at 0.5% (12x dilution of household bleach is effective if they are soaked (20 min). Peroxide products are also effective. Conventional growers see 2013 Commercial Vegetable Recommendations for additional options.
Source: extension.psu.edu