Squash Pests & Diseases

Squash, including winter squash, summer squash, zucchini, and pumpkins, are a mainstay of the summer garden. They are very productive, delicious, and nutritious. However, they also have more than a few pests and diseases to contend with to be successful. The most common issues these crops face in garden in the St. Louis area are squash vine borers, squash bugs, and downy and powdery mildew.

Although these are common issues, the first thing to consider is growing a squash that resistant to the issues you are having. This is by far the simplest way to deal with these issues as well as the way with the least amount of issues. Cucurbita moschata varieties are resistant to these issues, and tromboncino squash and Seminole pumpkin are highly resistant to all of these issues. There are also many other varieties that you can search for that have been selected for resistance to downy and powdery mildew. (Both tromboncino squash and Seminole pumpkin seed packets can be found in our online store.)

If, however, you can’t or don’t want to grow resistant varieties, or if you still have issues with them, then there are things you can do to reduce problems with vine borers, squash bugs, and mildew.

Squash Vine Borers

These are arguably the most destructive issues for squash because if you miss the signs, the plant can go from looking fine to being dead overnight. If your squash has gone from looking fine to the whole plant being wilted in a short period of time, then squash vine borers are what your problem is. We have a whole blog post that goes into detail about the best ways to deal with vine borers that you can check out here.

Squash Bugs

Squash bugs are the most talked about squash pest, and are by far the most visible pest, that can reach insanely large populations if left unchecked.

The first thing you can do to reduce squash bug issues is to trellis your squash. Squash bugs like the dark, sheltered, humid conditions that squash growing on the ground create under the leaves. This will not eliminate squash bugs by any stretch, but it does make their life harder. It also makes it easier to see the eggs, which is critical to reducing squash bug pressure. Once your squash gets going, you will want to regularly scout your plants for squash bug eggs. They are pretty easy to identify as they are small oval eggs that are brown/bronze in color. They are laid in clusters, usually on the underside of the leaves where two veins meet, although they can be laid anywhere on the leaf. When you see these eggs, you want to smash them. This can be a little harder than it sounds, so when you do this, make sure the eggs are actually smashed and not just rubbed off the leaf. (If you are unable to smash them, just remove them from the garden space.) If you keep up with smashing the eggs, especially if it’s a variety of squash that is very vigorous or otherwise less susceptible to squash bugs, this could be enough to keep the number of squash bugs low enough that they won’t be a significant problem.

If, however, this isn’t enough, then there are other things that can be done. One is diatomaceous earth. Diatomaceous earth (DE) will kill the young squash bugs and irritate adult squash bugs, but it will not eliminate adult squash bugs. Diatomaceous earth washes off so it will need to be regularly applied. (Diatomaceous earth and diatomaceous earth sprayers can be found in our online store.) To get rid of adult squash bugs, you can either hand-smash them or use pyrethrin-based sprays. There are no other organic sprays that will kill adult squash bugs. Due to this, the best approach is to use preventative techniques to keep the adult population low and only use the pyrethrin’s if all else fails and the population gets destructively large.

Mildew

One of the best ways to avoid mildew and increase yield in small spaces is to trellis the plants. Trellising the squash vines allows the plants to get much more air around them which keeps them drier, reducing the incidence of mildew. Similarly, avoiding watering the leaves can reduce mildew issues by reducing the amount of time the leaves are wet. So, if you trellis your squash make sure to water at the base of the plant.

There are a few other things you can do to avoid mildew. Neem, milk, and whey can all act as preventative fungicides to help prevent infection with mildew. Milk and whey can be used similarly to neem. The easiest way to do this is to use powdered milk or whey and just keep it on hand. You will mix a minimum of 2 tablespoons of powdered milk or whey powder into 1 gallon of water and then spray all surfaces of the plants on a sunny day. (Whey powder can be found in our online store.) Reapply neem or the dairy mixture every 10 days to prevent infection. If you have leaves that show signs of infection, cut those leaves off and remove them from the garden.