"With our recent rainy weather and storms, I am not surprised that we diagnosed late blight (Phytophthora infestans) in the University of Vermont Plant Diagnostic Clinic in late August. So far, it has been found in a garden and a high tunnel only on tomatoes although this aggressive pathogen can also attack potatoes, depending on the strain of the organism."
This destructive fungal-like organism was the cause of the Irish potato famine or the "Great Hunger" in the 1840s. If you have an Irish last name, you may be here as a result of your ancestors being among the million souls who left Ireland during the famine to search for a better life in America.
The pathogen cannot survive Vermont winters but typically blows in on storm fronts from the south or gets introduced on infected transplants, as occurred in Vermont in 2009. Late blight symptoms can appear on the foliage, stems, and fruit.
Leaf symptoms first appear as small, water-soaked areas that expand rapidly to form purplish blotches. The spots usually show up on the upper foliage first since the spores "rain down" during weather events. The disease can be hit or miss in an area, depending on where rain events have occurred.
When humidity is high, rings of whitish, spore-forming structures appear on the edges or undersides of the blotches. You can place suspect tomato tissue in a plastic bag with moist paper towels overnight and check for these rings of spores. Infected fruit remains firm and may exhibit whitish spores during high humidity. It should be destroyed and not be eaten or used for canning.
Read more at: www.samessenger.com