Why are potato leaves turning yellow? What should I do?

Many gardeners believe that yellowing potato leaves are normal and do not try to find out the reasons for this change and combat it. This is incorrect, as yellow tops can be a sign of a variety of problems that often lead to crop failure. We'll examine the main causes of this phenomenon in this article.

Reasons: Potato tops turn yellow

Two causes immediately come to mind: disease and pests. However, yellowing of the tops can also be caused by non-parasitic diseases, as well as by simple environmental conditions and improper care. It's important to investigate all possible causes so that timely action can be taken.

Humidity and temperature

For normal growth of root crops, a moderate climate, average temperature and high humidity are most suitable.

Most often, the lower leaves of potatoes begin to wilt due to drought. Gradually, the yellowing spreads to the entire plant. At temperatures above 30 degrees Celsius, the potatoes begin to die. To reduce the impact of heat on the root crop, loosen the soil around it regularly to ensure oxygen access. However, heavy watering won't help here—it will only create a crust on the surface, causing the plant to suffocate. However, combining loosening and watering is possible.

Water stress also has a detrimental effect on potatoes: the leaves begin to turn yellow from the bottom, then from the top, the flowers fall off, and the plants simply dry out. It's recommended to adjust the irrigation system so that the soil moisture level is always around 70%. During flowering, this level should be at least 75-80%.

Lack of fertilizers

This problem is most common in areas where potatoes are planted year after year. The soil gradually becomes depleted, resulting in a lack of nutrients, most commonly potassium and phosphorus. To replenish these micronutrients, the area should be fertilized in the fall, after harvest. The best fertilizer in this case is nitroammophoska, which should be applied generously to the soil. It's also a good idea to rotate the potato planting site at least every 2-3 years to allow the soil to regenerate.

Plants may also turn yellow due to a lack of iron and manganese. Fertilizers containing these nutrients should be selected and applied to the potato planting area. However, keep in mind that overfertilization can also negatively impact the yield.

Diseases

Yellowing tops are often caused by various root diseases. Let's look at the most common causes.

Phytophthora

If the lower leaves of a bush turn yellow, pay attention to the condition of the leaves. If their edges have darkened and a fluffy coating has formed on the underside, the potato is most likely infected with late blight. This disease causes the entire bush to turn yellow, reducing the number and size of tubers. If the disease is detected, the bushes should be treated with fungicides, such as copper oxychloride. It's best to remove the most damaged plants from the area.

Fusarium

With this disease, the upper leaves begin to turn yellow and curl. Gradually, they begin to fall off, and the stem turns brown. However, this begins even before the leaves wither, so when yellowing appears, it's worth making a cut in the stem; with fusarium wilt, the inner part of the stem will already have changed color. Affected fruits will begin to rot during storage. The only solution is to uproot and discard all affected bushes.

Verticillium wilt

Symptoms of the disease include wilting and curling of lower leaves, wilting of young shoots, and dark spots on the stem cut surface. This disease can also only be controlled by removing infected bushes. To prevent this wilting, young bushes should be treated with a copper oxychloride solution.

Dry spot (macrosporium)

Yellowed foliage and elongated or rounded yellowish or brown spots on the leaves are the main signs of macrosporiosis. The spots continually enlarge. The disease is caused by a fungus and leads to the complete drying out of the plant, while the fruits fail to develop and remain small. Treatment with specialized chemicals is the only way to combat the fungus.

Ring rot

The thin stems and foliage of the potato plant begin to turn yellow. Over time, they dry up and fall off. To confirm the diagnosis, dig up and cut open the affected plant's tuber: it will have brown or yellow rings encircling the fruit near the skin. In advanced cases, the fruit will be rotten and will secrete mucus when squeezed. All diseased plants should be removed, and the remaining ones should be fertilized with potassium and nitrogen fertilizers.

Blackleg

Leaves that turn yellow and curl around the midrib may also indicate blackleg. However, the main signs of the disease can only be seen in the tubers: they turn black and begin to rot. The roots and lower part of the stem also turn black and begin to rot. Diseased bushes should be dug up and burned, and the area where they grew should be treated with Bordeaux mixture or a mixture of ash and copper sulfate (1 liter of ash to 1 tablespoon of copper sulfate).

Pests

Potatoes are often attacked by harmful insects and worms. Here are the two most common types.

Colorado beetle

The Colorado potato beetle is a scourge for many gardeners. Its presence can be identified by seeing the insect itself or its eggs—tiny orange specks on the leaves. Gnawed potato tops are also a sign of the pest's presence. This insect causes irreparable damage by eating potato leaves—the vegetable grows slowly, fails to thrive, and dries up.

To prevent Colorado potato beetle attacks, plant cilantro, calendula, beans, and tansy near your potato plot. You can also regularly spray the plants with a strong infusion of mint, basil, garlic, or dandelion. The strong scent of these plants repels the pest.

If beetles appear, serious measures must be taken. Chemical pesticides include Mospilan, Komandor, Bankol, and similar products. These treatments should be carried out three times during the potato growing season, but the last one should be carried out no later than 21 days before harvest. It is also recommended to treat the plants weekly with fungal or bacterial agents to kill the larvae. These include Boverin and Fitoverm.

Nematodes

Nematodes are helminths that live in the soil and feed on tubers and roots. They consume the underground portion of the potato plant, killing the plant. Signs of a nematode infestation include yellowed small leaves, brown streaks, and growths on the tubers. If there are a significant number of nematodes, quarantine the area: remove the potatoes, treat the field with chemicals, and do not use them for at least five years.

To prevent nematodes, add urea to the soil before planting and sprinkle lime on the soil after harvest. Also, after planting, fertilize the potatoes with liquid chicken manure. Oats, peas, lupines, or rye should be grown near potato crops.

Infested potato bushes are dug up and treated with bleach. The remaining potato plants are treated with Bazudin.

Non-parasitic diseases of potatoes

The third group of root crop diseases are non-parasitic. Let's take a closer look at them.

Iron and magnesium deficiency

A magnesium deficiency causes the lower leaves to become lighter and turn yellow. This deficiency reduces yield, and the remaining tubers contain little starch, significantly affecting flavor. To combat this deficiency, apply magnesium fertilizer to the soil.

Iron deficiency also causes leaves to turn pale and yellow, their edges and tips darken, and the leaves die. This doesn't significantly impact yield, but it still damages the root crop. Iron-rich fertilizers are needed.

Bronzing of leaves

Bronze leaf disease is caused by potassium deficiency. It manifests itself as dark green foliage early in growth, after which the leaves turn bronze, wrinkle, curl, and dry out. This disease should be controlled in its early stages by fertilizing plants with potassium fertilizer. Bronze leaf disease typically occurs in peat or floodplain areas, and also after liming. Hot, dry weather is an additional risk factor.

Nitrogen deficiency

The effect on the root crop is the same: the leaves turn yellow and dry out, the fruit tastes worse, and their yield decreases. The foliage is small and often irregularly shaped. Nitrogen fertilizer is required. Interestingly, excess nitrogen also negatively affects potatoes: they begin to grow very vigorously, acquiring a rich green color, but the yield decreases.

Phosphorus deficiency

A phosphorus deficiency in potatoes causes weakened branching, weakening, and slow growth. Brown edges appear on the tips of the lower leaves, and brown spots appear on the tubers, with streaks extending down to the skin. This disease significantly affects the potato's flavor and leads to fruit rot. The best control method is liming the soil.

Reviews

Why are potato leaves turning yellow? This question is very popular on vegetable gardening forums. Let's find out what gardeners have to say about this problem.

Gertrude writes:

"If it were an early variety, it would turn yellow uniformly, all the bushes at once. But if bushes of the same variety look different, there's clearly an external problem. Most often, yellowing is caused by drought. In this case, the unevenness is due to different varieties, fertilizers, etc. Or it could be a disease (mole, virus, nematodes, etc.)."

Nina writes:

"The leaves may have turned yellow due to a lack of water, especially if the summer is hot and the potatoes aren't being watered enough. Only a quick watering will save the situation. Or maybe you're using too much herbicide if you're using it to control weeds. And, of course, the tops turn yellow as the potatoes ripen. If yours turn yellow in the fall, it's time to harvest."

Elizabeth writes:

"I remember in 2006, all my potatoes died. It was a shame – we left the dacha, came back a couple of weeks later, and everything was already yellow... It turned out Colorado beetles had eaten them. Then we didn't plant anything in that area for three years, and we cultivated the surrounding land. So, constantly inspect your beds; if you see Colorado beetles, you need to start getting rid of them right away..."