Yellowing leaves on squash

Why Are My Plants Turning Yellow?

It happens to all gardeners.

One day you wake up and realize your tomato plant’s leaves are yellow and you have no idea why.

Don’t panic! We are here to help you answer that daunting question of “why are my plant’s leaves turning yellow?”

Use the infographic below to understand what your plant might be trying to tell you through different types of yellow leaves. After the graphic, we’ll explore a little more in depth of why leaves turn yellow and brown, and how to give your plants the nutrients they need to stay green.


This work is licensed under a Creative Commons Attribution-NoDerivs 3.0 United States License.

Common Reasons Leaves Turn Yellow

1) Waterlogged vs. Dehydration: The most typical reason your plant’s leaves turned yellow is because of water, but it’s tricky to understand whether you are over-watering or under-watering the plant. Often the leaves of plants that are under-watered will be crispy with a slight curl to the leaf while over-watered leaves will be limp.

However, the plants leaves could be deceiving. You might be watering your plant enough but the water just isn’t getting to the root, which would show signs of dehydration. This often causes gardeners to waterlog their plants, harming it even more. Take action by improving soil drainage with sand or replant to a raised bed.

2) Lack of Sunlight: Since plants differ on how many hours of direct sunlight they need, lack of sunlight is another common reason leaves turn yellow. If you know you’re watering your plant correctly, it might be time to adjust the location of the plant if possible.

3) Pest Problems: If your plant’s leaves are yellow with holes or pieces of the leaf missing, you have a plant eating pest on your hands. Easily eliminate the bug without harming your plant by using neem oil or an insecticidal soap.

It’s Not That, So Why are My Plants Turning Yellow?

If you’ve knocked out the above possibilities then it’s time to take a closer look at your leaves. While it’s not mentioned on the infographic above, sometimes plants can turn yellow because of fungus or disease such as early blight or septoria leaf spot. Use one of our garden fungicide products to prevent and stop fungus growth on your plants.

Plants require 13 essential minerals that they absorb through the soil. The yellow pattern on your leaves could indicate which vital nutrient your plant is missing. The nutrients plants need most are nitrogen, phosphorus and potassium.

Secondary nutrients required by plants include calcium, magnesium and sulfur. Many of these elements can be found in fertilizers or compost that you can apply to the soil of your plants. Calcium and magnesium are also found in lime.

Plants need a small amount of boron, copper, iron, chloride, manganese, molybdenum, and zinc. These trace elements are often found in grass clippings, tree leaves and other organic matter that you can compost and later add to soil once again.

The best thing to do when your plant’s leaves get yellow spots or turn yellow, brown, or black is to get your soil tested to determine which nutrients your plant is missing.

Yellowing Squash Leaves: Why Squash Leaves Turn Yellow

Your squash plants were looking wonderful. They were healthy and green and lush, and then one day you noticed that the leaves were getting yellow. Now you are worried about your squash plant. Why are the leaves turning yellow? Is that normal or is something wrong?

Reasons and Fixes for Yellow Squash Leaves

Well, I hate to be the bearer of bad news, but chances are, if your squash plants leaves are turning yellow, something is wrong. The hard part is figuring out exactly what. The leaves on a squash plant will start to turn yellow any time the plant is stressed. Below, I have listed a few reasons why a squash plant may be stressed.

Lack of Water

While squash plants are pretty hardy plants, as far as vegetable plants go, they do need about 2 inches of water a week. Sometimes they will need more due to high temperatures. Check to see if your squash plants are getting at least this much water a week. If not, supplement natural watering (i.e. rain) with a sprinkler or a drip hose.

Vine Borers

Vine borers will attack a squash plant and make its way through the vine of the plant. Tell tale signs of a vine borer include yellowing of the leaves, gradually from the base end of the vine to the tip, and a small pile of “sawdust” at the base of the vine, near where it comes out of the ground. If you suspect a vine borer, be aware that pesticides will not work. The only effective, though not always successful, treatment is to try to remove the vine borer worm from the stem. Go to the spot where you suspect the vine borer is lodged and carefully slit the vine lengthwise (in the direction of the capillaries). This will not hurt the squash plant too much and either way, if you don’t find the vine borer, the plant is doomed anyway. If you’re able to locate the vine borer, use a toothpick to pierce and kill it.

Iron Deficiency

Without iron, plants have a difficult time making chlorophyll, the substance that makes leaves green. Adding iron chelates (a kind of fertilizer) to the soil can help. Most of the time, iron deficiency is a result of the nutrients being leeched out of the soil due to over watering. Make sure that you aren’t overwatering your plants.

Bacterial Wilt

Unfortunately, if your squash plants are infected by bacterial wilt, there’s nothing you can do to save them. The yellowing of the leaves will be followed rapidly by wilting and browning of the leaves and eventually death. Bacterial wilt can be diagnosed by cutting off a piece of the stem and squeezing out some of the juice inside. If the juice comes out slimy or oozing, then the plant has been infected. Destroy the plants and don’t compost them. Don’t plant squash or other cucurbit vines in that location next year, as the bacterial wilt will still be in the soil and will infect them as well.

While the conditions listed above are some of the most common reasons for squash plants developing yellow leaves, they aren’t the only ones. As stated above, the leaves on squash plants will turn yellow any time the plant is stressed. If you can find out what is stressing the plant, than you’ll be able to remedy the situation and help your squash plant regain its green coloring.

Five Reasons Squash Leaves Turn Yellow

The Stress of Insufficient Water

Insufficient water to the roots of a squash plant can result in leaves turning yellow. Squash plants require about 2 inches of water per week. During the fruiting stage of growth, the plant may require more water, especially in hot, dry weather. To encourage deeper roots, water squash plants less often but more deeply.

The Stress of Iron Deficiency

An iron deficiency (chlorosis) should be suspected if the leaf veins of the squash plants are green but area between the veins is yellow. A lack of iron availability, not deficiency, is a more accurate description of the problem. Here are natural methods of correcting the availability of iron in soil:

  • Lower soil pH.
  • Correct clay soil by adding organic matter.
  • Improve compacted soil.
  • Correct overly wet soil.
  • Reduce phosporus in soil.

The Stress of Bacterial Wilt

Erwinia tracheiphila, a bacterium, is a cause for loss of cucurbit plants including squash. The first clue that your plant may have bacterial wilt is leaves turning dull green, wilting in the day, and recovering from wilting at night. Leaves will then begin to turn yellow, wither, and die. Unfortunately, this process continues, killing the entire plant.

Bacterial Wilt is spread by the spotted and striped cucumber beetles. Some of the beetles contract the bacteria from eating infected plants. The bacteria overwinter in the guts of beetles. The bacteria is spread by the infected beetles’ mouthparts and their fecal matter. Controlling the beetles is the only effective way to prevent bacterial wilt.

The Stress of Squash Vine Borers

The flow of vital nutrients and water is halted by the damage of the piercing-sucking mouthparts of the squash vine borer. Efforts should be made to eliminate the borer from the squash plants as soon as possible.

The first line of defense is preventing the adult borer from laying its eggs. If eggs are laid, they can be removed. Sometimes the borer succeeds with laying the eggs and larva enter the vines. The only remaining possibility of successful removal now is this:

  • Cut a slit in vine near borer.
  • Remove borer.
  • Cover the cut stem with soil.

The Stress of Mosaic Viruses

There are two mosaic viruses that infect squash plants: squash mosaic (SqMV) and zucchini yellow mosaic virus (ZYMV). Cucumber beetles are the usual carriers of the squash mosaic virus: aphids spread the zucchini yellow mosaic virus. The key to preventing the spread of mosaic viruses is controlling cucumber beetles and aphids.

What Causes Yellow on Your Leaves of Your Squash Plants?

Squash image by nix pix from <a href=’http://www.fotolia.com’>Fotolia.com</a>

Planting a garden provides food for the family. However, it is disturbing when the squash plants you have worked so hard to grow get yellow spots on the leaves. These yellow spots could indicate disease or they could indicate some other problem that you can easily solve or prevent in future gardens.

Water

Give your squash plants enough water. Although squash plants are fairly hardy in the heat, a lack of watering can cause the leaves to turn yellow. To prevent the leaves of your squash plants from turning yellow, make sure they get about 2 inches of water per week. If there is a lack of rain, plan on supplementing. You can either use a hose or sprinkler with fresh water or use old dishwater if your community is experiencing a drought. Empty the dishwater into a bucket each day and then water your squash plants. Make sure to water the base of the plants and not to pour water onto the leaves. You may need a little bit more water if the weather is exceptionally hot. Make sure to water in the early morning or in the evening to allow the plants to soak up the water before the hot sun can evaporate it. Too much water, especially in cooler weather can cause the leaves to yellow as well.

Bugs

Look for evidence of vine borers when you notice that your squash leaves are turning yellow. The leaves begin to yellow where it attaches to the vine first and then the yellowing works out to the rest of the leaf. You can also tell if it is a vine borer problem if you see vine sawdust at the base of the plant. Sometimes you can remove the bug and save the plant, but more often than not, the plant damage is too great to save it.

Soil Deficiencies

Make sure your soil has the proper nutrients before planting your squash. The soil needs to have plenty of iron. Treat your soil with a fertilizer or compost before planting seeds or seedlings to prevent yellowing leaves. Too much watering can also deplete the iron in the soil. Keep your waterings to about 2 inches a week. If your soil is deficient in iron, purchase a liquid iron from your garden supply store and add that when watering your plants.

Disease

Bacterial wilt is common in squash plants, which also causes yellowing in the leaves. To determine if your plant does in fact have bacterial wilt, cut off just a small piece of vine and split it open. If the “juice” inside seems more slimy than watery, it is indeed bacterial wilt. There are no cures for bacterial wilt. Remove the affected plants immediately to prevent the disease from spreading. You may also want to do some extra composting or fertilizing in this garden area and refrain from planting anything in that particular spot for a year.

Cucumber and zucchini leaves yellowing and wilting

I would liquid feed them.
Meanwhile, do a soil test to ensure the pH is at the proper level.
link to Univ. of MD recommended soil labs:

We recommend Univ of Deleware as the best choice, on the list, for testing vegetable gardens because they will test for lead. Lead is a chemical of concern in a veggie garden.
If your garden is new soil than it might be a lime problem.
Not matter the plants look fertilizer deficient. Over watering could cause similar conditions but you would have to work hard to over water a raised bed of your nicely textured soil.
Liquid plant fertilizer is equal to the intravaneous feeding they give people arriving at the hospital emergency room. If you pour it over the plant foliage it will be immediately absorbed!
If your plants look different after performing this two consecutive days then you will know it is a nutrient deficiency. Follow the directions on the plant food of your choice, using the dilute solution listed on the label.
A soil test will take a few weeks and that will tell you what to do next.
Joyce
Harford County Extension Office, Forest Hill
410-638-3255

Learn About Zucchini

Common Zucchini Disease Problems

Alternaria Leaf Spot: Small, round reddish brown spots, usually with a yellow halo, form on the upper surface of the leaves. Severely infected leaves turn brown, curl upward, wither and die. Fruit are not usually infected but can suffer from sunscald due to leaf loss. This disease is worse in warm, wet or very humid weather. Burpee Recommends: Avoid getting water on the foliage. Remove infected plant parts and do not work around wet plants. Provide plenty of air circulation. Contact your Cooperative Extension Service for fungicide recommendations.

Anthracnose: This is a fungus disease that attacks the fruit as it is ripening. Irregular brown spots develop on the leaves. Infected fruit develop sunken black spots that may have white mycelia during wet weather. The spots enlarge and turn black; the fruit rots. Extended periods of heat and humidity facilitate anthracnose growth. The fungus overwinters in diseased plant debris. Burpee Recommends: Provide sufficient space between plants for good air circulation, avoid overhead watering which can spread the fungus spores, keep a clean garden, remove and discard all diseased plant material and rotate crops.

Bacterial Wilt: Leaves turn brown, stems wilt and shrivel, the infected plants die. Burpee Recommends: Remove and destroy plants showing signs of the disease. Control cucumber beetles, which spread the disease. Contact your Cooperative Extension Service for recommendations.

Mosaic Virus: Young leaves are distorted and mature leaves will have an intensive mottled appearance. Fruit can have yellow spots or bumps. The disease is quite serious and be transmitted by aphids or cucumber beetles. Burpee Recommends: Remove and destroy any infected plant. The virus can overwinter in weeds so keep the garden clean. Monitor and treat for aphids and cucumber beetles. Contact your Cooperative Extensions Service for recommendations in your area.

Powdery Mildew: This fungus disease occurs on the top of the leaves in humid weather conditions. The leaves appear to have a whitish or greyish surface and may curl. Burpee Recommends: Avoid powdery mildew by providing good air circulation for the plants by good spacing and pruning. Contact your Cooperative Extension Service for fungicide recommendations.

Common Pest and Cultural Problems for Zucchini

Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.

Blossom End Rot: Ends of the squash gets soft before they are ready to harvest. This can occur when there is not enough calcium in the soil or when root damage and water stress reduce the uptake and movement of calcium through a plant. Burpee Recommends: To avoid BER, properly site and prepare your garden bed before planting. Most crops need full sun and loose, well-drained organic soil. Test your soil to see if calcium is recommended. If it is, apply lime in the recommended quantity according to manufacturer’s instructions. Avoid planting too early in cool soils as this can inhibit early root development, making the plant more susceptible to BER. Avoid wide fluctuations in soil moisture by applying 2-3 inches of mulch. This will moderate the release of water to plant roots, and also keep the soil from drying out when it is directly exposed to the sun.

Cucumber Beetles: Beetles may be spotted, striped or banded and can be very harmful. Beetles are usually ¼ to ½ inch in size. Beetles start feeding as soon as they hatch and can kill or slow the growth of the plants. Beetle larva can also bore through the roots of the plants. Beetles can also transmit diseases from plant to plant. Burpee Recommends: Knock off adults into a jar of soapy water and destroy them. Spade the soil to destroy dormant beetles before you plant. Use a row cover to prevent adults from feeding on young plants. Consult your Cooperative Extension Service for other insecticide recommendations.

Spider mites: These tiny spider-like pests are about the size of a grain of pepper. They may be red, black, brown or yellow. They suck on the plant juices removing chlorophyll and injecting toxins which cause white dots on the foliage. There is often webbing visible on the plant. They cause the foliage to turn yellow and become dry and stippled. They multiply quickly and thrive in dry conditions. Burpee Recommends: Spider mites may be controlled with a forceful spray every other day. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for miticide recommendations.

Squash Vine Borer: The brown headed larva will bore into stems, feed through the center of the stems, block the flow of water and the plants will collapse and die. The first sign of this pest is that the plant will wilt during the day and perk up at night. Check the base of the plant for holes and you will see what looks like sawdust. Burpee Recommends: Pull and destroy any plants killed by squash vine borers. Row covers will prevent the female from laying her eggs. In most areas there is only one generation each year so a second crop can be planted in early July. Although you can’t always save the plant, as soon as you see the wilting plant, cut a slit in the stem above the hole using a sharp knife. Kill the borer with the tip of the knife, or pull it out. Mound soil over the cut area and keep the soil moist. New roots may grow and the plant may live. Rotate crops. Consult your Cooperative Extension Service for insecticide recommendations.

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