Pests and Diseases of Summer Veggies

— Written By and last updated by

There isn’t much that can quite compare to the taste of home-grown vegetables. However, it takes time and dedication to achieve such a delicious bounty of produce. If you are an avid vegetable gardener then you know that growing vegetables isn’t just a stroll through the field and stumbling upon pungent peppers, scrumptious squash, or toothsome tomatoes. In addition to maintaining a steady supply of water and fertilizer there are many pests and diseases that can be the bane of any gardener’s existence.

Picture of squash vine borer moth.

Squash vine borer moth

Vegetables such as squash, zucchini, and cucumber all reside in the cucurbit family. These vegetables have several pests and diseases that can otherwise burden healthy growth. One such pest that attacks squash and zucchini is the squash vine borer. An effective indicator of the insect is the sudden wilting of your squash or zucchini plants. These pesky critters can be devastating to your crop if not properly managed. If wet, sawdust-like material is present at the base of plants then the squash vine borer isn’t far behind. Borers are small white grubs about an inch long. The adult moth lays eggs at the base of squash and zucchini seedlings in late April through mid-May. As the eggs hatch, they then eat their way into the plant. It tunnels inside the plant for several weeks before emerging as a large grub to pupate in the soil. The borer subsequently hatches June – July as a beautiful orange colored moth which then proceeds to lay more eggs on unsuspecting squash and zucchini. There can also be a second generation that emerges in mid-August.

A picture of Squash vine borer damage

Squash vine borer damage

Once you notice the damage it’s too late for control and pesticides are useless since the grub is within the plant. If you’re careful you can take a wire and thread through the tunnel the borer created and attempt to kill it by continued poking. A knife can also be used to slit within the squash stem to try and locate and remove the grub. If this approach is taken be sure to mound soil around the wounds you created. The plant will begin to grow roots from the area and attempt to recover. Another approach is to wrap the stems of young seedlings in aluminum foil to prevent the moth from laying eggs and then remove the foil as the plant matures. Apply pesticides such as spinosad or liquid carbaryl at the base of the plants in May and August for effective management before the eggs hatch. Always be sure to follow the label directions for any pesticide application.

A picture of powdery mildew on cucumber.

Powdery mildew on cucumber

A fungal disease that is common on cucurbits, peppers, and other vegetables during the summer is powdery mildew. Powdery mildew forms a white coating over the upper surfaces of leaves. Infection usually begins on the lower, older leaves first and then slowly spreads across the entire plant. As the disease increases in coverage, leaves start to senesce and fruit quality and yield are affected. This disease prefers moderate temperatures of 70-85°F, high humidity, dense foliage, and low light. This disease can also develop under relatively dry conditions. The fungal spores can be spread by wind over long distances. Practices to discourage disease include use of resistant cultivars, adequate plant spacing to encourage air flow, weed and debris removal that may harbor the pathogen, and application of fungicides to protect the crop. Products containing the active ingredients copper or chlorothalonil (the trade name of one product with chlorothalonil is known as ‘Daconil’) are the best and only effective products available to you as home gardeners. In addition, select varieties with tolerance to the disease.

A picture of early blight of tomato.

Early blight of tomato

Tomatoes can also have their share of problems. These red beauties can succumb to the diseases of blight and wilt. Early blight shows up on the lower leaves of plants as necrotic spots that resemble a bull’s-eye. The disease can live in the soil on old plant debris and can splash up onto the plant when it rains. This is why mulches of plastic, straw or newspaper are recommended in the vegetable garden. Early blight will also infect the fruit causing circular sunken lesions. Remove infected leaves and fruit from the garden. As home gardeners, you can reduce disease by trellising tomatoes to increase air flow and prevent spores splashing up from the soil and prune the bottom-most leaves as the plant grows. Late blight is another disease detectable by irregular water-soaked lesions on newer growth. It eventually attacks all parts of the plant. It does not live in the soil, but will overwinter in potato tubers or is carried by the wind from a nearby infected area. This is why crop rotation is imperative! There are no cures for these blights, but chemical fungicides of chlorothalonil or mancozeb can slow their spread. As mentioned before, always follow the instructions on the label for mixing and application of any chemical product.

A picture of late blight of tomato.

Late blight of tomato

Remember that pests are attracted to stressed plants so be sure to keep plants happy and healthy with adequate sun, water, and fertility. Keep in mind that most summer vegetables need a minimum of six hours of sunlight each day. Also, include flowering plants that support beneficial insects to provide a natural control to potential pests and aid pollination. To help alleviate wet leaves focus your irrigation on the soil and root area. This is achieved through the use of soaker hoses and drip irrigation that helps reduce any standing water on the foliage. Learn to distinguish plant damaging pests from beneficial insects including pollinators such as bees that help fruit set, predators such as ladybird beetles that eat pests, and parasitic insects such as small wasps that lay eggs on pests. Remove dead and diseased plants and discard in the trash. Remove weeds before they flower. Do not let weeds go to seed! Stay on top of challenges with a stroll through the vegetable garden every day or two.