Controlling Zucchini Insects: Learn About Zucchini Pests

By: Bonnie L. Grant, Certified Urban Agriculturist

The amazing bounty of zucchini is undoubtedly one of the season’s greatest pleasures. These squash are one of the most prolific producers and zucchini growing problems are rare. They are, however, prey to numerous insect pests whose feeding activity can seriously damage the crop. Zucchini pests range from the tiny aphid to the ½-inch (1.3 cm.) squash bug, but the damage to the plants can often result in death. Early detection to find zucchini bugs on plants is crucial, as some of these pests can kill the vines in just a few days.

Zucchini Growing Problems

Most gardeners have a good laugh at the size some of their zucchini fruit attain. It stops being so funny when the fruit is taking over your garden and you can’t seem to give the stuff away quick enough. That type of exuberant growth should be celebrated and lauded, and it would be sad if anything happened to stop the consistent march of produce.

Unfortunately, some insects do plague the plant and jeopardize the harvest. Identification is important as each pest has a different treatment. For instance, you can’t just say the plant has zucchini worms when it is more likely some species of larva or caterpillar. Here are just a few of the most common zucchini bugs on plants.

Vine borers and worm-like zucchini pests

Zucchini plants that look limp are often falling victim to any number of fungal diseases. They can also be experiencing the bite of the squash borer. Squash borers are hard to see because the hatched caterpillar crawls inside the zucchini stem. These hidden zucchini worms feed on the stem for up to 6 weeks before pupating and finally becoming adults.

Adults are a type of moth but more closely resemble a wasp. In addition to wilting plants, look for tiny holes in the stems and sticky black excrement. Early treatment as adults are laying eggs is the best way to control borer. Use neem oil every 3 to 5 days at the base of the plant from May through June.

Other worm-like pests of zucchini include:

  • Armyworms
  • Cabbage loopers
  • Cutworms
  • Leaf miner larvae

Other Zucchini Insects

  • Aphids are one of the most common of the pests that affect zucchini plants. They are small winged insects that tend to mass together and leave sticky honeydew on leaves. Often ants are seen in tandem with aphids because ants feed on the honeydew. Zucchini aphids aren’t the only pest in town, though.
  • Thrips are another miniscule insect that you might need a magnifying lens to view. Thrip damage occurs from adult and nymph stages and their feeding can transmit tomato spot virus.
  • Flea beetles are tiny dark brown insects which jump when disturbed. In large infestations, the leaves will have shot holes through out. Heavy populations of flea beetles can diminish plant health or kill it.
  • Cucumber beetles are actually quite pretty but their damage can be serious. These insects are ¼- to ½-inch (.6-1.3 cm.) long, bright yellow with black spots. Leaves, stems and fruit will become scarred and damaged from this insect’s feeding.
  • Squash bugs are another common pest of zucchini. Nymphs are greenish gray and adults are brownish gray. Female squash bugs lay copious quantities of bronze colored eggs on the underside of leaves. Feeding causes speckled yellowish brown leaves, wilting, stunted runners, distorted or dead fruit.
  • Stink bugs are similar in form but smaller and cause pinpricks on fruit with yellow halos. These areas become necrotic and mushy.

Most of these insects can be controlled by using row covers, practicing good weed management and using appropriate insecticides or horticultural oils and soaps for chemical free controls.

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What are those bugs on your squash? Squash bugs, probably. Here are tips on how to identify, control, and get rid of squash bugs in your garden.

What are Squash Bugs?

Squash bugs can be the bane of a gardener’s existence! They are very difficult to manage and can cause a lot of havoc. Squash bugs are most commonly found on squash plants (hence the name) such as zucchini, winter squash, and pumpkins, but they may also affect other crops in the cucurbit family (like cucumbers, cantaloupe, and watermelon). Other pests that are commonly found on squash include squash vine borers.

Squash bugs are often mistaken for stink bugs, as they are similar in appearance and both have a foul odor when squashed. However, stink bugs are wider and rounder than squash bugs.

Monitor Pollination

The Spruce / K. Dave

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In addition to having to manage the short lifespan of zucchini blossoms, you also will need both male and female flowers open at the same time. Only female flowers set fruit. The male flowers are there strictly for pollinating purposes.

New zucchini plants tend to produce a lot of male flowers at first.   This can be frustrating for gardeners when they see a lot of flowers blooming but no fruits forming. Be patient. Once the plants mature a little, they will start setting flowers of both sexes. And thanks to the early male flowers, there already should be plenty of pollinating insects in the area. You will know you have female flowers when you see tiny fruits directly behind the base of the flower.

If you’re really dedicated to your zucchini harvest, you can always take pollinating matters into your own hands. You can remove the male flowers and dust their pollen onto the female flowers to help ensure good pollination takes place. You can also use an artist's paintbrush to transfer pollen from the male flower on the the female bloom. Moreover, don’t waste those early male flowers. You can still pick them, dip them in batter, and fry them up for a great treat.

How to Keep Your Zucchini Bug Free

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Zucchini (Cucurbita pepo var. cylindrica) is one of the fastest-growing and most productive summer squashes -- when you keep it bug free. Producing cylindrical, thin-skinned green or yellow fruit, zucchini is an annual vegetable that starts fruiting 35 to 55 days after sowing. According to the Missouri Botanical Garden, its many potential pests include whiteflies, aphids, squash vine borers, cutworms, leaf miners, stinkbugs and spider mites. Pests weaken and kill zucchini plants by feeding on their sap and destroying plant tissue, and some pests transmit diseases. Use a combination of strategies to protect your zucchini plant from bugs.

To see the undersides of leaves easily, attach an old mirror to a hoe and hold it under the plant. Sticky leaves and a sooty black coating are signs of whitefly infestation.

Grow your zucchini plant in a different place from the previous year, and change growing sites each year as often as possible to help prevent the buildup of insects in the soil.

Remove any old organic mulch from around your zucchini plant. Mulch attracts seedcorn maggot larvae, and adult squash bugs overwinter in it. Spread a 1-inch layer of fresh compost every month instead.

Check your plant every three or four days for bugs or their eggs and destroy them by squashing them between your fingers.

Cover your zucchini plant with a single layer of horticultural fleece as a barrier to bugs. Hold it in place with stones and gather the fleece beneath the stones to create a tight, firm edge against the ground. Remove it when the squash begins to flower to allow bees access for pollination.

Place wooden boards on the ground next to the plant. Leave them overnight and check them every morning. Wipe off and crush any bugs.

Sprinkle diatomaceous earth around the base of your zucchini plant. Reapply after rain.

Spray the base of your plant weekly with the biological control Bacillus thuringiensis var. kurstaki, or Bt, says Cornell University College of Agriculture and Life Sciences, as it attacks caterpillars and squash vine borers.

Spray a ready-to-use insecticidal soap over all parts of the plant, including the undersides of leaves, to control whitefly, spider mites and aphids.

2. Bacterial Leaf Spot

Bacterial leaf spot is caused by Xanthomonas campestris bacteria. It starts as small spots on leaves that form a small yellow margin. These spots grow and merge, eventually becoming necrotic.

It also causes small, beige, indented spots on zucchini fruit.

It thrives in hot, moist weather and attacks plants through wounds or openings in the plant. It usually hits during the summer when temperatures are high.

How to Deal with Bacterial Leaf Spot

The most important step for preventing this disease is to buy certified disease-free seed, since leaf spot is a seed-borne pathogen. The second most effective preventative measure is to rotate your crops every two years.

If you catch this disease early enough, you can apply a copper-based fungicide to control it.

Once it catches hold, there isn’t anything you can do. Pull your plants and destroy them to avoid further spread of the disease.


Plant squash and zucchini plants in a new location. If you're a creature of habit, it's time to add some change to your garden. Plant your squash and zucchini (both hollow stemmed plants) in a new location.

You want to avoid those dormant vine borers from attacking your new plants. Vine squash borers are only after your hollow stemmed plants, so plant cucumbers or peppers where your squash were last year as these plants won't be affected by vine borers.

Wrap the bottom of your squash and zucchini transplants with Ace Bandage. This way, even if the eggs are laid at the base of your plant, they cannot penetrate the bandage to feast on the plant itself.

Ace bandage does a good job of sticking to itself, so there's no need to wrap it incredibly tight. You want your plant to still be able to grow, so be sure to check the bandage each week or so and loosen as necessary. (Also be sure to add more bandage as the plant grows.) I've also seen folks use this wrapping method with aluminum foil.

Wipe the stems. Keep a watch at the base of your plants. If vine squash borers have been an issue for you in the past, keep an eye out. Whenever you're working in the garden, simply wipe or rub the bottom of your plants to get rid of any eggs that may be there.

Charcoal in the soil. In a past Southern Exposure Seed Exchange catalog, they recommend mixing a small amount of charcoal in with the soil where the zucchini and squash are planted. This helps reduce their numbers. Or you can place boards around the base of your plants in the evening, and in the morning, lift the boards to find the borers underneath. Then get rid of them.

Dixie Cups Collars- Yankee Homestead has a great video about using simple Dixie cups to prevent the vine borer moth from laying eggs. Simply pop out the bottom of a dixie cup and use it as a collar around the base of your plant. This will prevent the borer moths from being able to land and lay eggs supposedly. I will definitely be trying this method next year.

Watch the video: Squash Bug Control

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