Watch Out for These Common Potato Diseases & Pests, If You Want a Healthy Harvest of Spuds

One potato, two potato, three potato, four. Yes, this a children’s game, but it might also be the chant of potato diseases and pests that are ready, willing, and able to chow down your crop of spuds.

Do pests eat potatoes? Yes, pests like Colorado potato beetles, slugs, and wireworms eat the tubers, while lots of other pests attack the foliage of potato plants. Then there are the potato diseases and blights that can decimate your harvest.

And they told you growing potatoes was easy? Actually, it can be. All of these threats to your potato patch can be handled with a little preventive action on your part. I’ll walk you through the most common potato diseases and pests that affect plants and teach you how to avoid problems so you still get a big, healthy harvest.

Common Potato Pests

You love baked potatoes. Your family loves homemade French fries. But we can add a long list of pests that love potatoes to that list, too. Let’s look at the most common potato pests, how to recognize them, and what to do if they show up in your garden.

1. Colorado Potato Beetles

With a name like “potato beetle,” you might think this pest is laser focussed on potato plants, but you would be wrong. Adult Colorado potato beetles overwinter in the soil, then in spring, they emerge and look for a host plant.

Potatoes are their favorites, but any plant in the potato family will do, including tomatoes, peppers, eggplants, tobacco, and some types of weeds. The adult is a small beetle with an oval, yellow body and black stripes on its wing covers. Larvae are bright pink with black heads.

Both adults and larvae feed on the potato leaves, but the worst damage is caused by third and fourth instar larvae. These large larvae can take all leaves off a potato plant within 48 hours. This is a lethal situation for flowering potatoes, since even a 6% defoliation can kill the plant.

Use an insecticidal spray, like this one from Bonide that's specifically formulated to beat Colorado potato beetles, to combat these common potato pests.

2. Potato Leafhoppers

Potato leafhoppers are not an issue while they are young. Adults are yellow-green and very tiny, while nymphs are even smaller and don't have any wings. Leafhoppers become a problem when reproduction begins and then is continuous. These pests produce three to four generations a season.

Potato leafhoppers have leaf-sucking mouth parts. They suck juices from the potato plant causing the veins to turn pale and the leaves to curl. After a while, the leaf tips turn yellow and suffer a condition known as “hopperburn,” stunting the plant and limiting the yield.

Insecticides work well for these pests, too. Treat the crop the first time you find a scattering of nymphs. Spray plants with a multipurpose insecticidal soap spray, like this one from Bonide. Keep a close eye out for leafhoppers from mid to late May.

3. Aphids

It’s a rare gardener who isn’t familiar with aphids. These common vegetable garden pests are small and green or black and found in groups on the underside of leaves. The adults turn into fiends in spring looking for an acceptable plant, like a potato plant, to eat.

When they find one, they move right in and make themselves at home, losing their wings, sucking juices out of the plant, and giving birth to another generation that quickly gives birth to another.

No plant does well when their plant juices are being extracted. Potato plants wilt and crops are destroyed. Look for light green spots on the upper leaves and curling of the leaf margins. At this point, tuber yields can be reduced as much as 60%.

The sustainable integrated pest management solution: bring in natural enemies of aphids. My favorite is the ladybug, but other less “cute” bugs work too, like lacewing larvae, hoverfly larvae, and parasitic wasps. Don’t use pesticides for other pests, however, because these predators are very sensitive to insecticides.

You can actually buy ladybugs to attack aphids on Amazon.

4. Wireworms

Wireworms are click beetle larvae and they look like little pieces of wire. They're slender, yellow-brown, and around 1 inch (2.5 cm) long. They are hungry around the time of potato seeding and will feel on the seed pieces soon after planting. Their population is larger if your garden was formerly sod or laid fallow the prior year.

Test for wireworms by burying a handful of untreated wheat, corn, or potatoes in the soil about a month before planting. Flag the location and then 10 days later, dig up the bait and take a look.

If more than one wireworm is found on the bait, take action. If you don’t act, the wireworms will feed on seed potatoes, seedlings, and even your tubers. One way to combat the wireworms is to trap them and kill them.

Take pieces of raw potato, then “plant” them in the soil. Check the traps every week and pick off and kill any wireworms on them.

Common Potato Diseases

That’s not all, folks! Even when you do what you need to keep insect pests at bay, your potato plants can fall victim to some common potato diseases. To spot these, you don’t have to dig up the tubers. They often show up on the foliage first. Here are the four most common potato diseases to watch for.

1. Late Blight

Late blight of potatoes is one of the most critical diseases to address. It is caused by a fungus that can infect foliage, stems, and tubers. It can also spread all over the garden in the wind. Look for irregular dark spots that get larger over time.

On the upper side of a leaf, the dark area is surrounded by a green halo and on the underside, you might see white mold. When the tuber is infected, you’ll see dark brown or purple spots.

The best way to control blight on potatoes is an integrated approach. Start off with a potato cultivar that has some blight resistance, like these 'German Butterball' tubers from Burpee. It's also vital to keep sources of the fungus, including other infected crops, far from your potato patch.

Disease is likely when you experience two consecutive days with a temperature of at least 50°F (10°C) and six or more hours of 90% relative humidity. This means your blight risk is high. Use a fungicide, like this one from Bonide, to prevent and treat problems if you experience weather that follows this pattern.

2. Early Blight

Early blight of potatoes, also called alternaria, is a soil-borne fungal pathogen that affects a variety of crops. Look for concentric rings of lesions on the leaves that appear a few weeks after foliage emerges. The disease starts as very small spots on lower leaves which then coalesce into larger marks.

Alternaria causes lesions on the leaves which often have a target spot appearance of concentric rings. Small dark dots appear a few weeks after emergence on the lower leaves, then grow and kill the leaf tissue.

You can help prevent this disease by removing debris and weeds from your garden. Crop rotation can also help. Don’t let your plants become stressed, since stress will increase the impact. If the problem spreads fast or impacts many of your plants, treat with a fungicide like the one above.

3. Common Scab

Three to six weeks after potato tubers start growing, the surrounding soil must be moist. If those tubers are growing in dry soil during this stage, they can get infected with common potato scab, which is an unsightly blemish disease. Lesions start small and coalesce into bigger irregular areas and turn colorless to dark brown.

Scab often results from lack of irrigation, a lack of light, poor-draining soils, or dry weather. If the cause is simple, so is the solution. Water potato plants one or two times a week for the first month after tuber initiation. It also helps to use fine-textured and well-draining soil, plant clean seed potatoes, and use crop rotation.

4. Blackleg & Soft Rot

Blackleg is a major potato disease that is caused by several of the same bacterias that cause soft rot in potato tubers.

The foliage is first attacked by blackleg and then you may see rolled upper leaves, blackened stems at ground level, and stunted pale-green or yellow foliage. It can also cause a slimy green-brown rot and the collapse of potato stems. Blackleg symptoms vary according to the prevailing weather conditions.

In potato tubers, the rot starts from infected wounds, lenticels, and stolon ends. Over time, you will also see soft, wet, cream-colored tissue with a sharp demarcation between diseased areas and healthy areas. Over time it develops a foul smell.

There is no proven chemical treatment for blackleg in potatoes. The best bet is to use good cultural practices, like using certified disease-free seed potatoes, not overwatering your plants, and disposing of any infected plants the minute you discover them.