Vegetable Garden Pest Update
Posted: August 11, 2012
Symptoms of downy mildew on pumpkin include chlorotic lesions on the upper leaf surface that then become necrotic with charcteristic purplish-gray sporulation on the underside of the leaf surface. Photo: Beth K. Gugino
Here are a few late summer pests that can still be a problem, so watch for them.
Late blight has been confirmed in tomatoes in Columbia County. Late blight is extremely destructive. The Columbia County field was thriving, late blight infected the plants and five days later they were dead. Fungicides help prevent late blight from infecting plants, but they will not stop it after the plant is infected.
Downy mildew is now common in cucumbers. Down mildew, like late blight, is blown in on wind currents. Downy mildew and late blight are in the same family of disease. Downy mildew attacks vine crops like cucumbers, melons, pumpkins, and winter squash. Cucumbers are very susceptible. Melons are moderately susceptible. Pumpkins are the most resistant, but they do get it. Again, the only way to prevent downy mildew is to apply a fungicide before the leaves are infected. The same fungicides that help prevent late blight on tomatoes and potatoes also help prevent downy mildew on vine crops.
Vine crops are also showing symptoms of powdery mildew. Powdery mildew is unrelated to downy mildew. Powdery mildew produces a white growth on the leaves. It starts out in circles, but soon covers the entire leaf. The white you see is actually spores that it releases to spread infection. Powdery mildew thrives in high humidity, but does not like frequent rainfall because the rain washes away the spores.
Overhead watering in this case actually reduces the amount of powdery mildew.
Finally, we are seeing more damage to vegetables from the brown marmorated stink bug. They attack the produce on the outside edges of the garden first. Pyganic is the safest insecticide that will control stink bug. You must hit the bug with the spray. Spraying the plants does not control stink bugs.
For more information contact your local extension office. In Lackawanna County call 570-963-6842 or email LackawannaMG@psu.edu
John Esslinger, Extension Educator
Penn State Extension