The leaves of a potato plant should be a healthy green color. A potato leaf turning yellow could be a sign of several different things. Below are some reasons why this happens and what you can do about it or prevent potato plant problems in the future.
Potato Leaves Turning Yellow
There are many reasons that your potato leaves may be turning yellow. Here are some of the most common:
Potassium Deficit
Potato plants need plenty of potassium to grow well and produce large, healthy tubers. However, if not enough potassium is available, the leaves will turn yellow, starting at the bottom of the plant moving up towards the top. You can help prevent this by planting your potatoes in soil rich in organic matter like compost or manure. This provides plenty of macronutrients, including nitrogen, phosphorus, potassium. If growing your spuds in containers, make sure you use a good quality potting mix with plenty of organic matter.
Leaf Miner Damage
Potato plants are susceptible to leaf miners. These small insects tunnel between the upper and lower leaf surfaces causing them to turn pale yellow or even brownish. It can be particularly common during wet summers when plant growth is fast. To prevent this from happening, use a floating row cover as soon as potato vines emerge.
You can spray Neem oil once a week until the potato leaves have hardened off. This is usually after around 45 days. If you notice any signs of infestation, remove affected foliage immediately so it does not spread to healthy leaves. Potatoes are also susceptible to another type of leaf miner called the leek moth, which feeds on the base of the stem causing young plants to wilt. This is more of a problem in warmer climates.
Heat stress
Potato plants are very sensitive to heat. They will often show signs of stress if exposed to abnormally high temperatures for prolonged periods. This causes leaves to turn yellow starting at the bottom of the plant, progressing upwards as conditions worsen. Avoid planting your spuds during an especially hot or dry spell unless you provide plenty of shade and keep the soil moist.
Waterlogging Damage
If roots become waterlogged, this can make potatoes bolt prematurely. This is when flowers appear on stems. However, tubers stop growing because conditions are unfavorable enough to support healthy foliage growth. It results in small or misshapen potatoes, which may even be poisonous. In the future, avoid planting your spuds in poorly drained soil or growing them in containers that do not have sufficient drainage holes.
Cold Damage
Potato plants do not like cold weather and will often show signs of wilt if temperatures drop below 50 F (10 C). Light frosts may cause leaves to turn yellow. However, you will unlikely see this until winter arrives unless extremely mild conditions. If you live in an area with a short growing season, try using black plastic mulch or row covers as soon as vines emerge from the ground to protect against late frosts.
Late Blight
potatoes are susceptible to late blight, a fungal disease commonly associated with warm, humid weather. Leaves may turn yellow overnight before dying, and black spots appear on the foliage. This often spreads quickly to stems and tubers if left untreated. Water splashes spread late blight spores. Avoid overhead watering if possible, or make sure plants are very well spaced out.
Nitrogen Deficiency
As potato plants grow, you will need to feed them with nitrogen-rich fertilizers to ensure large, healthy roots develop. If no nitrogen is available inside the plant, it will not produce chlorophyll. This leads to the leaves turning pale yellow or even white due to a lack of pigment. It can also cause stems to become weak and spindly looking.
Seed Piece Damage
If you grow your potatoes in containers, make sure to start them off in good-quality seed compost. Avoid peat-based mixes unless it specifies that they are suitable for potatoes. If spuds are grown directly in the soil, check they do not dry out or become waterlogged at any point during germination. Once shoots appear, remove all damaged foliage before thinning seedlings to around 12 inches (30 cm) apart. This should be done carefully to disturb the developing tubers.
Viral Diseases
Several different viruses can affect potato plants and turn leaves yellow. This may also cause stunted growth if left untreated. The most common of these is PVY. If your plants become infected, make sure to remove and destroy any affected foliage as soon as possible.
Resistant Cultivars
Potatoes can be bred to resist several common diseases that often affect the leaves, resulting in decent yields even when conditions aren’t ideal. If potatoes are grown organically, you might not get much in the way of disease-resistant spuds. However, this does not matter too much because healthy roots will produce fine tubers regardless.
Your Plants Aren’t Getting Enough Sunlight
Another common reason a potato plant’s leaves turn yellow is that they are not receiving adequate sunlight. In most cases, the undersides of these leaves will be pale green instead of yellow. If your plants’ leaves start looking more yellow as the days pass, then it could mean that they have not been receiving enough light lately for photosynthesis to occur.
You’ve Over-Fertilized Your Potato Crop
Sometimes a potato leaf will turn yellow because it has received too much nitrogen from fertilizers. If you have been fertilizing your plants with manures, composts, or other high-nitrogen sources, it may be time to switch to something lower in nitrogen, such as mulch hay which does not burn the roots as easily.
Bacterial Ring Rot
When a potato plant turns yellow, it may have contracted one or more bacteria called bacterial ring rot. If you notice the leaves wilt and turn yellow from the bottom up, this is an indicator that bacterial ring rot has taken root. The bacteria can be introduced when you practice poor crop rotation and inadequate soil preparation. It is important to remove these affected plants immediately and not harvest any potatoes or cultivate in the same area.
Potato Leaves Turning Yellow: Final thoughts
Green potatoes do not necessarily mean ripe or safe to eat. A potato leaf turning yellow is not something you want to see when trying to grow the best garden crop possible. You do not want anything to stand in the way of your harvest. A yellowing plant can signify several different problems with your potatoes as discussed above.