If you are new to planting and growing Potatoes, you may ask, “Why are my Potato plants yellowing,” which usually means it is ready for harvest.
However, sometimes yellowing may be a sign of underlying problems.
Therefore, beware of Potato plant chlorosis if it happens before the yield season is near.
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Why Do Potato Plants Turn Yellow? (Causes & Fixes)
Potato is probably the most promising garden crop because it can yield within 90-100 days of sowing.
However, Potato plants turning yellow before flowering or having a brown leaf appearance may indicate something severe.
To simplify it, we have highlighted probable reasons behind Potato plants turning yellow with some quick solutions.
1. Bacterial Diseases
Potato plants do not easily succumb to viral diseases unless the growing condition worsens due to poor soil health, overcrowding, and contaminated tools.
Sometimes, the lack of crop rotation and using infected seeds may also invite various bacterial diseases.
Therefore, you should know whether Potato plants turning yellow are from a disease accompanied by leaf browning, black spots, and stunted growth.
|Blackleg||It is caused by the bacteria Dickeya or Pectobacterium and invites wilting, yellowing, and blackening of the stem.
Infected plants may also produce fewer and smaller potatoes.
|Soft rot||It is caused by Pectobacterium and makes potato soft and mushy
Affected potatoes also emit a foul odor and yellowed leaves
|Ring rot||It is caused by the bacteria Clavibacter michiganensis and causes potatoes to have a brown, rotten center.
Infected plant witnesses stunted growth and yellowing leaves.
|Brown rot||It is caused by Ralstonia solanacearum and turns potato become soft and discolored.
Wilting, rotting smell, and yellowing are common.
Remember, continued high humidity or moisture can further accelerate the disease’s spread, affecting the companion plants.
- Remove infected plants: Severely infected crops should be removed and destroyed to prevent further spread.
- Antibiotic treatment: Antibiotics like streptomycin can stop the spread of the bacteria, but is typically effective if applied early.
- Use copper-based fungicides: Copper-based fungicides are more effective, but remember to apply fungicides according to label instructions.
- Crop rotation: Change the soil yearly to prevent a buildup of pathogens and pests.
- Cultural control: Using resistant varieties of Potatoes, such as Ranger Russel, Snowden, and Red Norland, can help to prevent bacterial diseases.
Pro Tip: Practicing good sanitation practices, using certified seed Potatoes, and avoiding over-fertilization help prevent the buildup of bacteria in the soil.
2. Wilt (Fungal Disease)
Potato plants are equally susceptible to fungal diseases or wilt, usually contracted from soil, water, and air, and sometimes from infected seeds.
Soil-borne fungi can survive for many years in soil and infect Potatoes when they come in contact with the roots.
On the other hand, water and airborne fungi occur when they come in contact with the foliage.
Generally, Potatoes are prone to two different fungal diseases or wilt, namely:
|Fusarium wilt||Verticulum Wilt|
|it is caused by the fungus Fusarium oxysporum.||It is caused by the fungi Verticillium dahliae and Verticillium albo-atrum|
|The lower leaves of the plant wilt and die first, while the upper leaves may remain green.||The symptoms may appear more uniformly across the plant, with a gradual decline in growth and eventual death.|
|The potato stem turns brown and become dry and brittle. The pith inside the stem may also turn brown.||The potato plant has a characteristic "zebra" pattern on the stem, with dark and light-colored rings alternating.|
|Low temperature accelerates the infection, but symptoms are most evident during hot weather.||It is more common in warmer weather and is more severe in acidic soil.|
In any case, yellowing of the lower side of the leaves and drooping are imminent, often advancing to bronzed appearance or black spots on the leaves.
Unfortunately, there is no cure for these diseases once they have infected a plant, but here are some effective preventive measures.
- Use-resistant Potato varieties: Some varieties are resistant to wilts, such as Russet Norkotah, Defender, megachip, and Gemchip.
- Crop rotation: Avoid planting in the same field for at least three to four years, as the fungi can survive in the soil for several years.
- Sanitation: Immediately remove and destroy infected plants to reduce the inoculum of the fungi in the soil.
- Fungicide applications: Fungicides can be applied before the disease has become established, once in the early growing season.
- Soil sterilization: Sterilize the soil with steam or chemicals to eliminate the fungal spores from the soil before using.
3. Potato Leaf Miners
Potatoes grown in the garden or yard are prone to Potato leaf miner (Liriomyza huidobrensis), a small fly that attaches to the leaves.
Once infected, the adult fly lays eggs on the undersides of leaves, and the hatched larvae begin feeding on the leaf tissue (chloroplast-rich mesophyll), causing necrosis.
Similarly, the damage points created by the miners can create entry points for plant diseases.
Keep an eye out for premature yellowing or browning of leaves and mines (small tunnels) in the leaves.
- Chemical controls: Apply insecticides to control the leaf miner population and continue the process every few days or weeks until they vanish.
- Cultural controls: Remove plant debris and affected leaves to reduce the number of leaf miner larvae present.
- Biological controls: Introducing parasitic wasps to the Potato field can reduce leaf mine infestation.
4. Potato Psyllid
Potato psyllid (Bactericera cockerelli) is another major problem for Potatoes that invites the yellowing of leaves.
Psyllid nymphs are insects less than 1 inch long that are attracted to Potatoes’ large, green foliage.
Once attached, they feed on the juicy leaves and introduce toxic saliva, which leads to diseased leaves.
Here is the list of damages that Potato psyllid can do to your Potatoes.
- Stunted growth: Psyllid feeding will suck nutrients out of the plant, causing stunted growth.
- Reduced yield: Heavily-infested Potato crops can experience significant, sometimes complete, reductions in yield.
- Transmission of diseases: The psyllid bites can invite diseases such as the “zebra chip” that causes dark stripes on the leaves.
Expect to find yellowing and curling leaves, with chances of psyllid eggs and nymphs present on the leaf undersides.
- Apply insecticides twice a week and continue until the insects disappear.
- Trimming off affected leaves and debris, or the entire plant, will be necessary to combat the spread risk.
- Introducing natural predators, such as ladybugs, can help reduce the psyllid population.
5. Late or Early Blight
Blight is a grave fungal disease that significantly impacts Potato crops and damages yields.
It may be why your Potato plants are turning yellow or brown with dark spots.
Here is how late and early blight can affect your Potatoes.
|Late Blight||Early Blight|
|Late blight is caused by the fungal pathogen Phytophthora infestants.||Early blight is caused by the fungal pathogen Alternaria solani.|
|Symptoms include dark lesions on the leaves and stems, which can turn black and necrotic over time.||Symptoms include brown, circular lesions on the leaves, which may have a "target-like" appearance.|
|It can spread rapidly and destroy entire potato fields within a few weeks.||It is less severe than late blight but still causes significant damage.|
|It is found when humid conditions collide with mild temperatures.||It is prevalent any time of the growing season, especially during high temperature.|
- Plant disease-resistant varieties of Potatoes such as Sarpo Mira, Sarpo Axona, Carolus, Orla, Toluca, and Amora.
- Practice crop rotation to avoid the buildup of pathogens in the soil.
- Remove infected plant debris and infected leaves from the field.
- Apply fungicides preventatively before symptoms of the disease appear.
- Monitor the field regularly for signs of blight and take action to control the disease promptly.
6. Mineral Deficiency
Potato plants are heavy feeders and need nutrients, especially NPK, magnesium, and iron, to produce high yields.
Therefore, beware of underfed Potato plants, which quickly exhibit yellow leaves, stunted growth, and chances of reduced yield.
The yellowing first develops on older leaves, and the plant produces a distinct purpling of the stem.
- The best approach is to apply a balanced fertilizer, such as a 10-10-10 fertilizer, at the first sign of deficiency.
- Otherwise, apply a foliar fertilizer to provide the missing nutrients directly to the plant leaves, especially nitrogen-rich food.
- Fertilize the plant two weeks after planting, then side-dress it with additional fertilizer once the plants have emerged every four weeks.
- Stop fertilizing two weeks before harvest is about to be ready.
7. Too Much Nitrogen
Although Potato plants love a high dose of Nitrogen, it does not necessarily mean you should compensate for other nutrients with nitrogen-rich food.
The reverse can also happen, where you over-fertilize your plants with too much nitrogen. Excessive nitrogen can cause dark green foliage or yellowed leaves while the veins remain green.
It can also cause leaf burn, stunted growth, and plant death in severe cases. Be wary about using liquid fertilizers rich in nitrogen content.
Similarly, homemade fertilizers like manures and composts tend to have high nitrogen content, and their over-application can be detrimental.
- If nitrogen toxicity is suspected, the first step is to reduce or stop nitrogen fertilizer applications.
- Irrigate the garden soil to leach excess nitrogen out of the root zone using flushing agents.
- Frequently water container-grown Potatoes with neutral pH water to leach excess salt.
- In severe cases, the affected plants may need to be removed and replaced with new, healthy plants.
- Replace compost or manure with something lower in nitrogen, such as mulch hay which does not burn the roots as quickly.
8. Waterlogged Soil
Tuber plants despise sitting in waterlogged soil as it deprives them of oxygen and nutrients.
Potatoes can bolt prematurely if Potato plant roots become waterlogged and induce flowering.
Mainly, the Potato tubers stop growing, and foliage succumbs to yellowing and wilting due to a lack of nutrients.
Beware of growing Potatoes in rainfall or flood-prone areas, as those waterlogged for over 24 hours become asphyxiated.
In severe cases, the plants may die. Therefore, overwatering is No-No.
- Reduce watering: If the soil is saturated, cut back on watering until the soil dries out. For container-grown Potatoes, cut back on watering and let them out in the sun to dry naturally.
- Improve drainage: Adding organic matter to the soil or creating raised beds.
- Add nutrients: Waterlogged soil is nutrient deficient, so add balanced fertilizer to the soil.
- Provide support: Waterlogged plants may be weak and prone to falling over, so providing support can help prevent further damage.
Monitor the plants closely and look for signs of recovery or further damage in the coming weeks; otherwise, remove the plants altogether.
9. Lack of Sunlight
Potatoes require at least six hours of sunlight daily to grow and develop properly; hence, finding a sunny garden spot is essential.
Those lacking ample direct sunlight may witness slower growth and lower yields due to limited photosynthesis.
You can tell your Potato plants are under-lit when the leaves become small and pale with yellowing and the stems are thin and spindly.
If the lack of sunlight is prolonged, the tubers will grow smaller.
- Relocate the plants: If the containers are in a spot with too much shade, it may be necessary to move them to a sunnier location, such as a patio, south-facing window, or garden.
- Prune nearby trees or shrubs: Prune nearby trees and shrubs to help increase the light that reaches the plants.
- Use reflective mulch: Reflective mulch can help enhance the amount of sunlight that reaches the Potato plants by reflecting light up to the leaves.
- Provide supplemental lighting: Additional lighting, using LED grow lights at least 10-12 hours a day, can help container-grown Potatoes thrive.
10. Temperature Stress
Potato plants are not hardy and may falter in cold weather. Likewise, it cannot withstand heat stress.
High temperatures can cause Potato plants to wilt, reduce growth, lower yields and invite yellowing leaves due to excess transpiration.
On the other hand, low temperatures can damage Potato plants and invite pale, turning yellow leaves, stunted growth, and blackened stems.
- For areas with short growing seasons, cover the Potato fields with black plastic or row covers to protect against frosts.
- Avoid planting the Potatoes too early in the season when frost is present. Otherwise, use raised beds or insulation (frost blanket) to keep the soil warm.
- To reduce temperature fluctuations, provide consistent watering and mulch around the Potato plants to help regulate soil temperature.
- Use shade cloth or better grow Potatoes in greenhouses or grow bags to combat heat stress’s effects.
From Editorial Team
Choose a Potato variety with characteristics better suited to your USDA zone and growing conditions.
Moreover, “hill” the plants by mounding soil up around the stems to encourage the formation of more tubers.
Planting each one slightly above another provides better aeration and nutrient supply, preventing the yields from becoming green or sunburned.