Potatoes are a mainstay of the American diet and they’re easy to grow even in small spaces, but that doesn’t mean they are immune to disease. Here are the most common potato diseases you might encounter and what you can do about them when they appear.
- Early Blight
Caused by the Alternaria solani fungus, Early Blight shows itself in June and July through telltale target-shaped brown spots on the leaves. The fungus will overwinter on old potato plants and in the soil, only to be eventually carried through the air to land on the wet leaves of existing mature potato plants – surprising given the name of the disease. Early Blight will not impact production, but it can be controlled by cleaning up and removing all potato plant leavings in the fall, planting good quality seed potatoes in a new area of the garden from the previous year.
- Late Blight
By far, Late Blight is the most devastating of the diseases of the potato. It favors cooler weather (60-80 degrees) with higher relative humidity of 90% or more. It grows in infected tubers and is airborne, easily being carried 5-10 miles from the point of origin.
To control late blight, always use certified, healthy tubers for seed potatoes and never leave cull potatoes to overwinter in the ground. When you see the signs of late blight (dark, oily spots on the leaves that get larger in high humidity), spray immediately with a fungicide and cut the plants off at the base. Destroy all parts of the plant to ensure that the disease is not spread further.
NOTE: Late Blight can affect tomatoes as well, so take care to protect nearby tomato plants should an infestation of late blight appear.
Blackleg is a bacterial disease that you may never see because most commonly it kills plants off before they ever emerge from the soil. When they do break through they will have yellowish-brown leaves for their short lives before they due.
Blackleg is usually caused by unfavorable planting conditions, so the best way to avoid it is to plant on dry days when the temperatures are above 50 degrees. A blackleg infestation cannot be corrected as it will kill every plant that gets it.