Squash - Guide to Common Pests and Disease

By Lara Wadsworth

Squash plants got you down? They are a Cucurbitaceae family member, which means they are afflicted by many of the same pests and diseases as cucumbers, pumpkins, and watermelons. This article is intended to identify the most common problems associated with growing squash plants rather than a list of ways to treat them. Once you know the problem, you can find the correct solution. For treating pest and disease problems, check out our pest guide or talk with a local extension office for specific treatment options.

Pests

The most common squash plant pests are aphids, squash bugs, spider mites, and squash vine borers. Regarding pests, the first instance of identification can be the most challenging, but as soon as you know what to look for, you won’t forget!

Aphids

Aphids are one of the most common plant pests in gardening. They are tiny sap-sucking bugs that can be green, red, black, and other colors. Yet, the body shape is always the same. They are tiny (1-3mm), have tear-shaped bodies, and reproduce quickly. They are often found on the undersides of leaves, new growth, and flower buds. Leaves may whither and curl but not turn brown. In severe cases, they will stunt plant growth. It is crucial to catch infestations early because of how quickly they spread and reproduce.

Squash Bugs

Squash bugs love squash! And, unlike aphids, they are easy to see with the naked eye. Squash bugs feed on plant flesh by sucking plant sap out of the foliage and other parts.

This can disseminate a crop of squash if not properly avoided. They can look different, but generally look like an elongated stink bug or even a large aphid. Removal by hand can be effective if there are only a few.

Spider Mites

Spider mites are another common plant pest across gardening and even house plants. They are teeny tiny little spiders that, instead of trapping bugs for food, suck out plant sap. They can cause curling of leaves and stunting of plant growth. They are one of the most difficult pests to spot when there are only a few because they are literally as small as the tip of a pin.

However, it can look like webbing in large infestations and tons of little chiggers running all over your plant. They can be red, brown, or tan but always spell trouble. They love hot, dry environments, so increasing humidity may help. But, if you already have an infestation, it is a good time to utilize multiple methods of control.

Squash Vine Borer

Squash vine borers are actually the larvae of a specific type of moth (the sesiid moth) that almost exclusively feed on cucurbits. The larvae are chunky, white, and literally take bites out of folithe age and budding fruits. The adult moths are sometimes mistaken for other types of bugs because they move strangely. Keep a keen eye out for either the larvae or the adults, and act quickly to avoid giving your crop up!

Diseases

The most common squash diseases are anthracnose, downy mildew, powdery mildew, and Blossom or End Rot. Anthracnose, downy and powdery mildew are all funguses that some plants can get in high humidity regions, or if the leaves get too wet too frequently.

Anthracnose

Anthracnose causes the leaves to turn brown in a spotty pattern. This picture features it on a grape plant, but the leaf damage will look similar in any squash or gourd plant. The fungi can also affect the stems or even the fruit in a similar way. Once a leaf or fruit is affected, there is no way to reverse the damage, but if you act early in the season, you can save the rest of your crop.

Downy and Powdery Mildew

Downy and powdery mildew have similar causes to anthracnose, including humidity and overwatering. It will look powdery and white. Downy mildew may also have yellowing or brown spots. These can be visible on the tops of leaves but show up first on the bottoms. Downy and powdery mildew are often treated in the same ways.

Blossom End Rot

Blossom end rot is a widespread disease that is not a disease at all. You will see the blossoms turning black, rotting, and not turning into fruits. Or, if they do turn into fruits, the end of the squash with the flower will start to rot.
A nutrient deficiency of calcium causes this. Once it has set on, it is impossible to recover the lost fruits or flowers. The best treatment is, unfortunately, prevention. However, if you catch it early in the season, a calcium supplement or soil amendment carefully mixed with water or injected can help limit its perpetuation. Ask your local garden center what options they have for this. A home remedy is finely crushing up eggshells and adding those to the garden soil.

A Healthy Plant Is A Strong Plant

Other problems that squash plants can face are being overwatered or underwatered, not getting enough sun or too much sun, and other nutrient deficiencies in the soil. Sometimes the thing that is wrong with your squash plant has nothing to do with a pest or disease at all; it is the environment it is trying to grow in.
An overwatered plant can look droopy but remain green, or entire leaves will start to yellow. Some yellowing and dying back of older leaves on squash plants is natural and normal; don’t be too concerned. If your newer leaves are yellowing or wilting, you could be overwatering.
An underwatered plant can, unfortunately, look similar to an overwatered plant. However, underwatering results in limp, wilting leaves that feel weak or soft to the touch, and when they turn yellow, they get crispy or brown along the edges. Luckily this is an easy fix! Adjust your watering schedule, and it should improve!

Sunlight

Sun exposure is critical to squash plant growth. In too little sun, the plant will struggle to grow at all. It may be halfway through the season, looking healthy, but has barely produced any flowers or leaves compared to your neighbor who has already started harvesting. It can be frustrating. Unfortunately, too little sun is often difficult to fix. Cut back nearby branches if possible, or even dig up the plant (being very careful not to disturb the roots or vines) and physically move it to a sunny spot that receives eight or more hours of sun daily.
In some cases (this is common with watermelons), too much sun exposure can sunburn your fruits! This is not a deadly issue but it can impact your fruit's quality. Avoid sunburn by ensuring the fruits are growing under a canopy of leaves or providing some other shade for the fruits, while still receiving the recommended hours of sunlight.

Nutrients

While this picture is not of a squash plant, it illustrates the issue very well. If you need to fertilize your squash plants, it will show first as slowed growth and then progress to yellowing and venation in the leaves. Most seasoned gardeners suggest fertilizing squash plants every 2-3 weeks. They can be heavy feeders, especially if your soil doesn’t have much nutrient density to start with.

Troubleshooting plant problems can be incredibly overwhelming. If you don’t find your problem in this article, I recommend narrowing the symptoms down to just a few key terms and searching the internet for possible problems. Don’t be discouraged! My former supervisor once told me, “To be a true horticulturalist, you have to kill a million plants.” So, don’t feel too bad if you get a failed squash crop this season, just make sure you’ve learned from it!