Just bidding their time

MAP PROVIDED Downy mildew has been building up on the DelMarVa Peninsula and was just recently identified in Mifflin County this week.

So far, the weather has been pretty good for area vegetable gardens. Timely rains with very warm temperatures should be resulting in squash, cucumbers, and sweet corn showing up on the dinner table.

But trouble is brewing in the South.

Two of our major vegetable diseases — downy mildew of cucurbits and late blight of tomatoes and potatoes — have trouble over-wintering in our northern climate. Their home base is in the Deep South where they can launch their deadly assault on vegetables every year. Movement is mostly coordinated with shifting weather patterns that provide transportation from their southern stronghold.

Science has advanced far enough that we can easily track their travels. With Extension educators from numerous land grant universities on the ground for verification, and the web-based applications that create disease-occurrence maps, everybody can be prepared for action.

Late blight has been observed in three Pennsylvania counties so far. The first sighting was found in early June and was confirmed by the Pennsylvania Department of Agriculture on transplants that were supplied from New York State to a smaller garden center in the far northeastern region of Pennsylvania (Susquehanna County). These plants have since been destroyed. Things were quiet then, until the disease was found on potato and tomato plants in York and Lancaster counties in late June.

Downy mildew was a no-show in Pennsylvania in 2016 but hit cucumbers hard in 2017. Could last year be repeated this year? The disease was just identified early this week in cucumbers in Mifflin County. It still is isolated, and conditions right now are not very favorable for spread. But past history shows that it will quickly spread across home gardens and then move into larger commercial fields once weather patterns change.

If you are interested in following the progression of these diseases in your area, the late blight map can be found at http://www.usablight.org/map and the downy mildew map at http://cdm.ipmpipe.org/.


Tom Butzler is a horticulture educator with the Pennsylvania State University Cooperative Extension Service and may be reached at