It’s not unusual for potato plants to turn yellow towards the end of their growing season. In fact, it’s a big indicator that they are ready for harvesting.
However, what if your potato plants begin to turn yellow early? This could be because of an underlying problem.
In this article, we’ll explore all the possible causes behind this troublesome behavior and how to counter them effectively.
What Causes Potato Plants To Turn Yellow?
The reasons can range from microbial infections to pest infestations.
1. Potato Psyllid (Bactericera cockerelli)
Potato psyllids are small insects (less than 1 inch long) that resemble cicadas. However, despite their small size, they can inflict irreparable damage to potato fields.
They can reduce the yield significantly. In severe cases, they can even cause the death of the plants.
When psyllid nymphs feed, they release a toxin from their saliva that introduces a disease called psyllid yellows to the plants.
As the name implies, the disease causes the plants to turn yellow, particularly affecting white and russet potato varieties.
The yellowing begins at the leaf edges and, over time, spreads to cover the whole plant. In blue and red varieties, the color becomes pink or pale purple instead.
Other symptoms include:
● Upward curling of tiny leaves on the top part of the plants.
● Wax-like pellets (called psyllid sugar) covering the leaves.
● Affected plants become stunted and pyramid shaped.
● Potato stems swell.
● Small potato tubers may form above ground.
How To Manage Psyllid Infestation?
First, check the underside of your leaves for the presence of psyllid nymphs since that’s where they feed.
They also tend to hide in concentrated numbers in lower, more shaded areas of the plant. You can also detect them with sticky traps.
Once discovered, you must treat the infested plants with either spinosad or imidacloprid. When using these pesticides, follow the instructions on the packaging for the method of application, rate of application, and safety precautions.
In severe cases, you might need to repeat the treatment several times before seeing results.
2. Verticillium Wilt (Verticillium dahlia)
Verticillium wilt is a fungal disease that leaves the lower leaves of affected plants yellowed and withered.
The symptoms of the disease spread upward to the younger leaves and cover the entire plant. Eventually, after the plant turns yellow, browning and necrosis set in.
Other symptoms include:
The disease thrives in hostile conditions such as drought, insect damage, nutrient deficiencies, and high temperatures (even though the initial infection only occurs in cool temperatures).
Once the plant is infected, its water uptake becomes limited. As a result, the signs of infection become more pronounced in hot weather and drought.
How To Prevent Verticillium Wilt?
The fungus stays dormant in the soil for a long time until conditions become favorable for it to grow. To prevent it from infesting your potato field, you should practice crop rotation with legumes, cereals, and grasses all year round.
Also, plant only certified and wilt-resistant potato varieties.
3. Fusarium Wilt (Fusarium solani f. sp. eumartii)
To an untrained eye, it’s sometimes hard to differentiate fusarium wilt from verticillium wilt because they share similar symptoms. However, one major difference between the two is that with fusarium wilt, the tissues between the leaf veins first turn yellow and subsequently brown.
Another way to tell fusarium wilt is to look out for the following signs:
These symptoms are more noticeable in drought and hot weather conditions when the potato plants are water-stressed. Over time, they will spread through the vascular tissues of the plant— the stems and tubers may begin to show a brown discoloration.
Like verticillium wilt, this virus can survive in the soil for a long time until it finds a suitable host. Once infection sets in, it spreads from the plant’s roots to the vascular tissues, affecting the stems, stolons, and tubers.
Prevention methods mostly overlap with those used for verticillium wilt.
4. Nutrient Deficiency
Deficiency in minerals like magnesium, nitrogen, and potassium will also cause your potato plants to turn yellow before harvest. This is because these nutrients make up the chlorophyll molecules needed for photosynthesis.
You can tell which nutrient your plant lacks by observing the symptoms.
During magnesium deficiency, the tissues between the leaf veins turn yellow while the margins remain green. The leaves at the bottom are usually the first to change color, followed by the leaves at the top of the stems. Eventually, the leaves become brown and die.
Nitrogen deficiency is straightforward to spot. First, the plant generally shows stunted growth and reduced yield. You’ll also notice thinning along the stems and unusually small leaves that turn yellow-green and drop prematurely.
In the case of potassium deficiency, older leaves first turn yellow, eventually turning brown at the tips and between the veins and margins. The symptoms then spread to the younger leaves— leading to yellowing, curling, wilting, and dropping.
How To Remedy Nutrient Deficiency?
Magnesium Deficiency
To cure magnesium deficiency, you can use DIY Epsom salt spray on your plants. To make this spray, dissolve two tablespoons of Epsom salt in 1 gallon of water. Apply twice or thrice during the season with one month gap between subsequent applications.
Also, you can fortify the soil during autumn or winter for the next planting season by adding calcium-magnesium carbonates or Epsom salt.
Nitrogen Deficiency
Using liquid plant foods is the fastest way to correct nitrogen deficiency. Tomato fertilizers, particularly, are beneficial for growing healthy potatoes. Follow the instructions on the label to know how much plant food your plant needs and how frequently you need to feed the plant.
You can also use all-purpose grow formulas to replenish the nitrogen concentration in the soil. Composting is also a great practice to boost nitrogen in the soil.
Potassium Deficiency
For potassium deficiency, you can also use liquid plant food. However, ensure it is low in nitrogen but rich in potassium and phosphorus. It’s also not a bad idea to add a layer of compost at least once a month.
Note that if you already regularly fertilize your soil with magnesium, phosphates, nitrogen, and potash, then you can rule out nutrient deficiency as the cause of your potato plants turning yellow.
Conclusion
Potato plants can start turning yellow for various reasons ranging from fungal infections to nutritional deficiencies.
It is vital to pinpoint the right reason by carefully observing the symptoms shown by the plants. Once you are sure, apply the correct remedy to eliminate the adverse factor.
