Potato Pests and Diseases
Potatoes can be bothered by a variety of pests and diseases. Here are the most common and what to do about them.
Damaging pests can work quickly in a potato patch. Stroll through the plot regularly looking for insects and the damage they cause. It's a lot easier to deal with a pest before it becomes a disaster. If you choose to use sprays or dusts to prevent or control a pest problem, read the directions and follow them carefully.
Colorado Potato Beetle
This pest is present and working in just about every state. Destroy any potato bugs you see and check the underside of leaves for their orange egg masses. Both the adults, which are yellowish with black stripes, and the larvae, which are dark red or orange with black spots, feed on potato foliage. Pick them off or spray Bacillus thuringiensis San Diego on the young larvae. Bt 'San Diego' attacks only the potato beetle larvae and is harmless to beneficial insects, animals and humans.
Flea beetles are tiny, black or brown, and pesky. They chew small holes in plant leaves and can do serious damage fast if they attack young plants. To foil these pests, cover young plants with fabric row covers as soon as you set them out. Keep flea beetle populations low through crop rotation and by maintaining high soil organic matter.
These tiny insects can transmit virus diseases. They suck juices from the leaves and stems of potato plants, injuring them badly. Insecticidal soap sprays are an effective control.
Wireworms are the larvae of the click beetle. They're a problem when potatoes are planted in a section of garden that was recently sodded. Fully grown wireworms are 1/2- to 1 1/2-inches long. They're slender, brownish or yellowish white and tunnel into plant roots and tubers, spoiling them. If your soil is heavily infested, contact your extension service agent for advice on solving the problem, or try growing your potatoes in the "tower" fashion mentioned in our article "Planting Potatoes."
You may have a disease problem in the potato patch one year and none at all the next. The weather plays a big part in the health of a potato crop. Moisture and temperature conditions may trigger certain diseases, which will spread rapidly through the potato rows. But there's no need to simply sit back and let the environment determine the fate of your crop.
To protect your crop, rotate the potato plot each year. Plant healthy, certified seeds. If you have severe disease problems, consider using a standard potato dust or spray regularly throughout the season. These are chemical mixtures that prevent some diseases such as late blight. They thwart some pests, too, such as the Colorado potato beetle. If you use a potato dust or spray, read and follow the directions carefully. To be effective, most standard dusts must be applied to the potato foliage every 7 to 10 days, beginning when the plants emerge from the ground.
If you have questions about diseases or pests, your local cooperative extension service agent can help you. Here are brief descriptions of a few of the common potato diseases.
The fungus that causes common scab lives in the soil for many years. It's not active, though, when the soil pH is below 5.4, so if you have a serious scab problem, take a soil pH test. You may want to lower the pH by not liming or adding wood ashes to the potato section of the garden.
Early blight injures foliage and reduces overall yields. Affected leaves develop small, dark brown spots that often grow in size, and which eventually kill the leaves. Gardens in central, southern and eastern states are most susceptible. Planting certified seed and mulching with hay can prevent this disease.
Late blight is caused by the downy mildew fungus -- Phytophthora infestans, which triggered the Irish crop failures of 1845 and 1846. You'll notice the disease first by water-soaked areas on the leaves that turn brown and black as the leaf dies. The disease strikes often during cool, wet weather and may spread rapidly if the weather warms up. Plants can die in a severe case, and potatoes can be seriously affected, especially in storage. Plant certified seed and use a potato dust to guard against late blight.
Aphids can spread mosaic viruses, which cause potato leaves to curl and appear almost two-toned (light and dark green). Mosaic occurs throughout the United States and cuts down on the harvest, but it won't kill the plants. 'Kennebec' and 'Katahdin' varieties have some resistance to certain kinds of mosaic.