Potato plant turning yellow

Why Do Potato Plants Yellow & Wither?

potato leaves image by Florin Capilnean from <a href=’http://www.fotolia.com’>Fotolia.com</a>

Potato plants add a touch of mystery to a vegetable garden. One watches, waters and wonders about what is actually occurring underground. Only when plants have definitely died does a gardener get to dig for uncounted treasure. In this case, yellowed and withered plants are signs of success. The only caution with potatoes is early onset of yellowing leaves and withering. As members of the nightshade family, potatoes are susceptible to all the diseases that plague tomatoes and that are characterized by early yellowing and withering. Keep your potatoes healthy during the growing season and wait for plants to signal your success.

Mineral Deficiencies

Like tomatoes, potato plants are sensitive indicators of soil nutrient content. Yellow or withering leaves may indicate the need for additional fertilizer. Deficiencies can include nitrogen, phosphorus, calcium, magnesium, potassium and boron. Adding potato-formulated fertilizer or compost will usually address deficiencies. If potatoes have been planted in the same area for several years, relocate them and spend a season restoring the soil.

Wilt Diseases

As members of the nightshade family, potato plants are prone to the same diseases that plague tomatoes. Both fusarium and verticillium wilt can produce yellowing leaves, withered stems and other signs of plant distress. Treatments include removing and destroying infected plants and leaving soil fallow for several years to insure death of wilt organisms.

Early and Late Blight

Tomato and potato plants share sensitivity to a group of fungal diseases known generally as blight. Recent infestations of blight in tomatoes serve as reminders of history: blight doomed the Irish reliance on potatoes in the 1840s and enriched America with waves of hard-working hungry immigrants. Blight spots on leaves tend to be dark and watery; they may, however, also display surrounding yellowed rings commonly referred to as haloes.

Prevention and Remediation Strategies

While there may be little you can do to salvage this year’s crop, planning ahead can improve future success. Using certified seed potatoes, rather than supermarket potatoes, reduces the chance of disease. Check further for certification of varieties bred to resist wilt (F1V1). Potatoes are also traditionally heavy feeders. Soil where potatoes have grown for several years need crop rotation and nutrient renewal. Soils infected with wilt or blight spores may need to be left fallow for at least one year and perhaps longer. Raising beds, improving drainage and not overcrowding plants all contribute to healthier growth.

Success Management

Late-summer or early-fall yellowing and withering of potato plants constitutes a happy ending. Plants die when potatoes are ready to harvest. Leave withered plants until they are fully dead to ground level; this may take a couple of weeks after plants have fallen over. Dig potatoes and spread them on brown paper or newspaper to dry for a week before storing.

Wait, That Plant is Drowning!

Did you know that over-watering is usually considered the most common cause of early plant death? In general, we are deathly afraid of under-watering our plants and as a result many of us tend to over-water. I am just as guilty of this as anyone else, although I am getting better. The best thing you can do to keep your plant healthy is to water it correctly.

How do you know if your plant is drowning? First, have you been watering only when the surface of the soil is dry to the touch? If you haven’t, it is possible your plant is staying too wet. For more information on proper watering for plants in pots read “Water Your Way to Happy Plants.” Second, is your plant looking light green and generally unhappy? One possible reason for this is over-watering. While both of these foliage indicators are symptoms of over-watering, the most common way someone figures out their plant is drowning is that the plant has wilted even though the soil is wet.

Why is over-watering so detrimental to plant health? Healthy roots are the foundation for healthy plants. Have you ever noticed that after you transplant a plant it will appear to sit there for a week or more before it starts growing? Well, it isn’t really just sitting there, it is establishing its root system. Once it has grown a substantial root system the plant starts putting its energy in growing a larger plant and more flowers.

Roots are important to a plant because they are its primary source of water and food and are also important for the uptake of oxygen. The roots of the plant take up water but they also need air to breathe. Over-watering, in simple terms, drowns your plant. Soil that is constantly wet won’t have enough air pockets and the roots can’t breathe. Roots that can’t breathe are stressed roots. Stressed humans are more prone to disease. Well, stressed plants are more prone to diseases too and one of the common forms of plant stress is unhealthy roots. Over-watered plants are likely to get root diseases, primarily root rot. You probably won’t know your plant has gotten root rot until you notice that it is wilted, but the soil is still wet.

What exactly is root rot? There are several different fungi that cause root rot. The most common culprits are Pythium, Phytopthera, and Rhizoctonia. Healthy roots should be white and clean looking. Roots with root rot are brown, grey, black, slimy or non-existent. Over-watering also tends to rob your plants of proper nutrition. Either the roots are damaged and can’t absorb the fertilizer in the soil or the excess water has leached the fertilizer from the soil. Either way the plant doesn’t have access to the food it needs.

OK, you’ve gotten this far and you think it is possible that you have been over-watering your plants. Now what? If the plants are showing some yellowing and you know they have been watered too much, but they haven’t started to wilt while wet, simply start following proper watering techniques and your plant should bounce back. Hold off on any application of fertilizer until you see new growth. Then I would fertilize with a water soluble fertilizer the next 2 to 3 times you water (after you see new growth) to increase the fertility level. After this go back to fertilizing every 7 to 10 days.

However, if your plant has jumped into the deep end even though it can’t swim (your plants are wilting even though the soil is still wet), then the plant is in much bigger trouble. If one plant in a combination planter is wilting and the others look fine you might want to consider removing the wilting plant to help keep the disease from spreading further. Begin using proper watering techniques . If the whole planter is wilting you will have to be more aggressive.

CPR for Drowning Plants

  1. Move the planter to a shady area, even if it is a full sun plant. The roots of your plant are unable to take up enough water to keep your plant hydrated. Plants in shaded locations will use less water. Once the roots are healthy move sun plants back to a sunny location.
  2. Be sure the pot is draining. If no drainage holes exists add some or repot the plant into a pot with drainage holes. Do not allow the pot to sit in water, this will keep the soil too wet.
  3. If possible, create additional air spaces around the root ball. One way of doing this is slowly tilt the pot to its side and then gently tap the container, the soil ball should now be loose within the container. Carefully re-stand the pot up when completed there should be small air pockets between the pot wall and around the soil ball. This will allow the soil to dry quicker and at the same time bring oxygen to the root zone.
  4. If the plant isn’t too large, repot into a different pot. Be sure to add new soil. This will give the roots nice, clean soil to grow into. If the plant is too large to be easily repotted go on to number 5.
  5. Begin watering only when the surface of the soil is dry to the touch. Do not allow the plant to get extremely dry, this additional shock could be enough to kill the plant. If the plant is wilting badly, you can mist or syringe the plant’s foliage with water which will prevent too much leaf scorch. Do not fertilize. With the roots in a delicate state it can be easy to burn the roots with fertilizer. Once the plant resumes active growth return to normal fertilization.
  6. Treating with a broad-spectrum fungicide can be helpful. Your local garden center should be able to help you choose one.
  7. If the plant is going to make it you should begin to see improvement in a week or so. Once the plant seems to be growing nicely move it into a sunnier location and begin fertilizing again.

Even if you take all of these steps there is no guarantee that your plant will bounce back. It partially depends on how badly the roots have been damaged. If you have a tendency to kill a plant with kindness and are composting more than are surviving you might look at changing your soil mix to a lighter, fluffier soil. Make sure you have plenty of drainage holes in your containers. If all else fails grow plants that like their feet in water. Plants like Cyperus, Alocasia, Colocasia, Acorus, and many others will thrive in containers that drain slowly. If you tend to keep plants on the wet side you might want to steer clear of plants that are more prone to problems from over-watering than most other plants.

For more information on general watering practices read “Water Your Way to Happy Plants.”

For more information on general watering practices read “Watering Container Plants.”

Ask a Question or Give Feedback about this article. 790 Readers Rated This: 12345 (2.9)

Dearest Nico,
Please help us! We have a few young seedlings, about four weeks old now, and they all have wilting or drooping leaves. The color is good, but the leaves are heavy and sagging. Some have wilted to nearly nothing. We water them twice a day. Please save our babies! Thank you!
— Margie & Anna V. via the mailbag at [email protected]

Greetings, ladies.
Thanks for writing us with a very good question. We actually get a ton of “leaf wilting” questions in the mailbag every month, so I am happy to finally answer this one!

It is important to understand that wilting/drooping leaves means that there is a deficiency somewhere within the plant. A deficiency can come from one or multiple areas (let’s hope it is just one). The primary areas a plant receives nutrition from are: light (photon energy), atmosphere (CO2 and O2) and medium (H2O and mineral nutrients).

An example of healthy plants, with leaves cupped upwards toward the light. (Photo by Nico Escondido)

Wilting/ drooping leaves are most commonly a sign of problems with water and/or nutrients. You did not mention any discoloration of the leaves, which is good, leaving us to focus mostly on hydration and not mineral deficiencies. But to start, we need to make a distinction between the terms wilting and drooping.

When it comes to drooping leaves, the issue is most often due to over-watering, believe it or not. Sometimes water stress, such as “drowned roots,” can cause abscisic acid to build up, closing down the leaf stomata and creating problems in both respiration and photosynthesis.

Wilting leaves, which is actually defined as having water loss or being dehydrated, is obviously associated with a lack of water. Wilting leaves will be dry to the touch and even a bit crumbly. Because you water twice daily and state the leaves are “heavy,” my guess here is the former—over-watering.

Over-watering can also cause the soil or grow medium to compress and suffocate the roots, which respire by breathing in oxygen (O2) during the dark or night cycle. The top third of the root structure contains air-specialized roots for this purpose (while the bottom third of the root structure is known as “water roots”). If the grow medium becomes too compacted, the breathable roots may lose their ability to respire and absorb oxygen, which they use to convert sugars to energy. Both the loss of oxygen and the build up of abscisic acid will severely weaken steams and leaves of the plant above the surface.

Now, if your plants are more wilting than drooping, meaning they are dry and crumbling, the issue is more likely to be under-watering. Test the soil for moisture content by pressing your index finger about an inch down into the medium. You should feel some moisture and coolness. While watering plants twice a day sounds like plenty of water, if you are only pouring in a few drops, it might not be enough.

An example of drooping plants, with heavy, wet sagging leaves. (Photo by Nico Escondido)

Generally, good watering practice dictates that you water each plant once, at the start of the day when the sun/ lights come up. Saturate the medium well, until you see the first drops seep out of the bottom of the container. That will be enough water for the day. It is also a good idea to let the medium become fairly dry—at least near the surface of the medium—before attempting to water the plant again. It is important to remember that while the plant itself breathes in CO2, the roots beneath the surface breath in oxygen (O2) during the night cycle. This is an essential part to healthy plant growth and development. And a dry, aerated medium goes a long way in allowing air to permeate the root zone and roots to breathe in their precious O2.

To fix the drooping, allow the medium to dry out overnight (completely) and use a thin stick (i.e., a skewer) to gently poke holes around the surface of the medium to help aerate—taking care not to damage any roots below. Poke around the edges, about an inch or two down, making a circling motion with the stick to make small holes.

Take another thin stick and use it as a support stake, if necessary. Stake it near the base of the plant and rest or tie the main stem to it. Make sure the plant’s main stem and branches are not thin and spindly. If they are, this could also be a sign they are stretching for light. Make sure your plant is directly under the light source and receiving around 18 hours of light per 24 hours to help it vegetate.

A semi-wilted leaf that is dry and cracking. It also has a mineral deficiency, most likely potassium (K). (Photo by Nico Escondido)

You are likely still a few weeks to a month away from being able to switch to a 12/12, light/dark cycle to induce flowering because of this setback with the drooping leaves. However, with some diligence and care, you can easily get your babies to bounce back and have a productive life cycle.

Very bad root rot can cause this. If you are able to look at the roots, then you can see if they are white or brown. If they are brown then it is root rot. But if the roots look white or slimy then you have either Fusarium disease which in most cases is like a blood clot that forms at the base of the plant & does not allow it to drink or you have Pithium which is also a root bound disease that looks like slimy boogers on the root system that does not allow the plant to drink.

Both of these diseases will also cause the plant to wilt during the day (or when the light is on) but at night (or when the light is off) the plants will stand back up. Both Fusarium & Pithium are known for destroying entire crops in 1 or 2 days. Root rot is easy to fix with 35% food grade hydrogen peroxide at 1 oz per gallon ran through the root system as a flush. Fusarium & Pithium you can try hydrogen peroxide but you will more than likely lose everything that gets it. The best thing to do for Fusarium & Pithium is not to get it with preventive measures like not taking air in from outside for your garden & always making sure keep your garden sterile (do not come home & go into your garden without showering & changing). You can start off with root rot & get Fusarium & Pithium.

What Is Potato Wilt: How To Control Wilted Potato Plants In The Garden

Nothing is more frustrating when growing potatoes than to find the plants suddenly wilting and dying in the garden. So what is potato wilt and how can you prevent wilted potato plants in the first place? Keep reading to learn more about controlling potato wilt disease and its causes.

What is Potato Wilt?

Verticillium wilt, also known as potato wilt, is a fungal disease that can be caused by either Verticillium dahliae or Verticillium alboratrum. Both of these fungi can survive in the soil, in infected plant parts and seed pieces for a long time. In fact, Verticillium dahliae has been found to remain in soil for up to seven years.

Wilt can result in a reduction in tuber size and stem-end discoloration. The fungus attacks the potato plant through the roots and interferes with the transportation of water. Potato plants exhibit disease symptoms when they turn yellow prematurely. Infected tubers may show vascular discoloration in rings near the end of the stem. Wilted potato plants eventually die.

Potato Wilt Disease Treatment

Some species of potatoes are more susceptible to wilt than others. Therefore, it is always best to plant potato varieties that are resistant to wilt. When shopping for disease resistant potatoes, look for labels with a “V” on them.

Controlling potato wilt is best done through prevention. Using high quality seed from fields that are free of wilt is an excellent starting point. Healthy plants are less likely to suffer from infection, so be sure to provide plenty of water and fertilizer which will help protect them from infection.

Keep gardens weed free, and pick up and discard all dead or infected plant debris. Crop rotation will also help with wilt management. Where there are large fields of potato plants wilting, the potato tops should be raked and burned.

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