If your tomato leaves, stems, and buds don’t look something like the healthy plants depicted in the photos at the right … and rather look more like tomatoes depicted at the Late blight on tomato site at Cornell University College of Agriculture and Life Sciences, some of your veggie growing dreams could be in for a dashing. Take the time now to study these photos … then head out to your plants and check the stems for sections of dark brown with white fungal growth, and check the leaves for brown sections with underside areas housing tiny white spores. If you see anything that looks like the photos in the link above you could very well have late blight. This is a serious fungal threat, not just to tomatoes, but to all nightshades – eggplant, peppers, potatoes. How big of a threat? Late blight is the disease that caused the Irish Potato Famine according to a fact sheet put out by Cornell Horticulture.
When I sat in on a web seminar hosted by people at Cornell, I learned late blight is highly destructive; once takes hold some of its pathogens can stay in surrounding soil for up to 8 years. This means any nightshade planted in that area is at risk for late blight for many years to come.
The same fact sheet goes into great detail about early stages of late blight – olive-green to brown, smaller to nickel-sized spots on leaves, fuzzy white fungal growth on leaf undersides , firm brown spots on tomato fruit. If you see this during weekly examinations, you can try to prevent its spread with fungicides, but most likely you will lose the plant.
DO NOT COMPOST diseased plants. Seal them in a plastic bag and let the bag sit in the sun to cook for several hours to kill the pathogens … or burn the plants if you have that capability.
Why sound the alarm about late blight now? It has been found in tomato plants purchased from big box stores in the Northeast, it can also be transmitted to and by peppers, eggplant, potatoes, any plant in the nightshade family, and by petunias, a nightshade cousin.
If you suspect a plant has early signs of late blight and seek confirmation, contact University of Connecticut Home and Garden Education Center for advice.