Identify and Deal With Potato Pests and Diseases

Late blight is a worldwide fungal problem and one of the most serious. The water mold, Phytophthora infestans, that triggered the Irish potato famine and crop failures of 1845 and 1846 also causes this disease.

It attacks during cool, wet weather but rapidly spreads as the temperatures rise. Signs include olive or pale-green areas on leaves that then turn black, with an oily or water-soaked appearance. Remove affected plants, place them in sealed plastic bags, and leave them in the sun to kill the foliage and the blight. Then dispose of the plant and any potatoes you harvested from it.

The name of this potato disease is misleading because it appears late in the growing season. Small, dark-brown spots on the leaves increase in size, and round lesions infect the tuber. This problem shows up in regions where warm weather moves between dry and wet conditions or where there is heavy dew or fog.

Mulching and proper watering techniques will help prevent early blight. Fungicides won’t eliminate it but can reduce its severity.

If you’re seeing wilted, dying, leaves and stems, you could be dealing with bacterial ring rot, which usually appears about mid-season or later. The wilting starts with yellow areas developing on the lower leaves, which appear burned. Cut a cross-section of an infected potato tuber, and you’ll see a ring of creamy yellow or brown rot.

Prevention is nearly the only defense against this nasty disease. Sanitize tools and equipment regularly, remove crop debris from the soil, and plant only seed potatoes that are certified against the disease.

The two bacteria that cause blackleg infection, Dickeya and Pectobacterium, thrive in the low oxygen environment of wet soil and spread as water moves through the soil. The issue causes tubers to rot in the ground or later, while in storage.

If you notice small, water-soaked lesions on the base of stems, and wilted, curly leaves that have a slimy texture, chances are, you’ve got a blackleg issue. Again, no chemicals can fight off this disease. Planting in well-drained soil and not allowing water to sit on leaves for extended periods helps prevent the problem.

Attacking young tubers, roots, stems, and the stolon, common scab is a soil-borne disease that stems from growing potatoes in neutral or alkaline dirt. Thin-skinned and early potato varieties like the Kennebec are most likely to develop it.

Symptoms vary, but the potato usually develops scab-like, raised patches on the tubers or root surfaces. Practice good soil management and crop rotation to reduce the risk of the disease — few reactive measures have proven effective.

These yellowish-orange, oval-shaped pests with black-striped wings love feeding on potatoes. During the winter months, they live underground. Then in the spring, the adults lay clusters of eggs on the undersides of leaves, which feed the larvae.

Prevent these pests by planting an early-maturing potato variety like Yukon Gold, growing potatoes every other year, and keeping the area weed-free. Pick off adults and larvae from the plant, then drop them in a bucket filled with soapy water to end their potato-munching days.

One of the most common garden pests, aphids not only destroy foliage but also spread potato viruses. You’ll most likely see these critters hanging out on the underside of the plant’s leaves. A major clue is the sticky, honeydew substance they leave behind on stems.

Garden predators like ladybugs are a great way to control them. Each ladybug will eat 40 to 50 aphids per day. You can also remove aphids by hand, then spray the leaves with water and insecticidal soap to deter them from coming back.

Click beetle larvae, or wireworms, live in the soil during the winter, then emerge in the early spring. They have a slender, yellowish-brown body and three pairs of legs behind their head. These destructive bugs can remain in the larval stage underground for two to six years, feeding on roots, bulbs, tubers, and germinating seeds. Heavy infestations will kill the plant.

Before planting, cultivate the top eight inches of soil thoroughly to expose any existing wireworms to weather and predators.

Though they usually stick to warmer climates during the winter, wreaking havoc in tropical and subtropical regions, in recent years, potato tuber moths have been migrating northward. The adults are small moths that lay eggs. Once the eggs hatch and reach adulthood, they become gray, pale green, or cream-colored caterpillars with dark heads.

Planting pest-free seed tubers, regular watering to prevent soil cracking, and timely harvests are the best ways to prevent these pests. Predators like the braconid wasp kill larvae. If needed, you can also use sticky traps to capture moths.

Golden nematodes love just about any plant in the nightshade family, including potatoes, and do the most damage during their larval stage. They find the roots of the plant, bore in, then suck out the juice, eventually killing the plant.

Nematodes can invade your garden via infected garden tools, flower bulbs, or seed potatoes. Plant nematode-resistant varieties to keep an infestation from taking hold. Rotate potato crops with crops that don’t attract the pests, like corn or soybeans, to help prevent the problem.