Zucchini is a favorite summertime crop, relatively easy to grow, and with a bounty of fruits for easy harvests and enjoyment. When all is going well, the vines produce all summer. When not, they may fall prey to common cucurbit pests with a penchant for the leafy vines and tender green fruits.

To keep up the prolific yields and beautiful, versatile fruits, setting the vines up for success includes meeting their preferred growing conditions to improve resiliency against pests and diseases. Zucchini is a summer squash (Cucurbita pepo) that performs best in full sun and organically rich, well-draining soils with even moisture.

Regular pest scouting is the first step in catching problems early on and in determining a management strategy. Plant zucchini companions and a diversity of blooming specimens to attract natural predators and other beneficial insects. They’ll pollinate the vines’ bright blooms while deterring common zucchini pests.

Cucumber Beetle

This insect is harmful to other plants in addition to cucumbers.

Cucumber beetles can severely damage plants beyond cucumbers, and are a significant zucchini pest. The adult beetles feed on leaves, blossoms, and fruits, while the larvae feed on roots and stems. Their swift feeding damages and kills the plant, especially young vines, in severe infestations. The beetles are also vectors for cucumber mosaic virus and bacterial wilt.

Cucumber beetles are chewing insects that consume all parts of the zucchini, from stem to leaf to fruit. You may notice their damage as irregular, jagged holes in the leaves.

The three main species of cucumber beetles include the banded (Diabrotica balteata), the striped (Acalymma vittatum), and the spotted (Diabrotica undecimpunctata howardi). Each is yellow to yellowish green with distinct markings. The larvae, white to yellow-white, may be below the soil level or boring into stems.

Treatment 

Picking off and hosing off bugs can make a big difference,.

Small populations may benefit from handpicking or hosing the pests off leaves and stems. Depending on the level of activity, it may be beneficial to do it more than once a day. Drop the beetles into a bucket of soapy water as you go.

Floating row covers help protect seedlings as they establish. They block the pests from feeding on tender growth. Remove the covers as the young plants mature and begin to flower to ensure pollination. Zucchini relies on multiple bee visits to produce fruit, but hand-pollination, too, boosts yields if covers are left on a little too long.

Pyrethrin sprays, spinosad, and neem oil treat the cucumber beetle. They’re most effective with regular treatments for transplants and seedlings during times of high beetle activity, though they impact pollinators and other beneficial insects as well.

Prevention

Try a late June planting to miss beetles active window. .

Keep beds weed-free around Curcibita pepo to reduce the spread of these zucchini pests. Grow flowering perennials like aster, yarrow, and coreopsis, and herbs like dill, parsley, and chamomile. These attract tachinid flies, soldier bugs, lacewings, and ladybugs that are natural predators of the eggs, larvae, and adult cucumber beetles.

You may also try a later planting to avoid the active season of the beetles. By mid-June, they emerge and move on to search for hosts. Planting late can help seedlings skip the larval feeding stage.

Squash Bug

These bugs appear in late spring or early summer.

Squash bugs tie with cucumber beetles for the most likely to damage zucchini. Squash bugs are sap-sucking insects that deplete leaves of water and nutrients. The foliage becomes speckled and eventually wilts, turns brown, and drops. Squash bugs (Anasa tristis) are common pests among cucurbits and other vegetables.

The large, gray-brown insects have flat, winged backs. Small, spidery nymphs are pale green with black legs and mature to a darker gray. The adults overwinter in sheltered spaces under logs, rocks, and debris to begin mating and laying eggs at the time host seedlings emerge. Clusters of eggs in yellow-orange appear on leaf surfaces and undersides.

Treatment 

Applying spinosad sprays or horticultural oils can kill the insects before they mature.

Horticultural soaps, oils, and spinosad sprays may eradicate early numbers of the nymph stage of these zucchini pests. The adults are tough to control as they travel, so catching them in the young phase offers the best success. 

Zucchini leaves are sensitive to horticultural soaps; use the most diluted listed recommendation sparingly, and avoid applying in direct sun.

Try removing eggs and nymphs by hand. Because eggs are difficult to crush, tear off the leaf portion that contains them. 

Elusive adults and nymphs take cover under mulch and in hiding places at the soil level. Place a board, shingle, or piece of cardboard near the stem to offer them cover. Lift it in the morning to expose and destroy the congregating squash bugs. To reduce protective cover, remove mulch from the area if the numbers are high.

Prevention

Schedule when to plant to avoid the insect’s active season.

If squash bugs are a problem in your area, try planting seedlings early in the season to establish before the insects become most active (usually in June) or late for areas with long growing seasons.

Practice good sanitation, clearing debris after the final harvest to reduce overwintering habitat for adults. Use temporary row covers to shield the zucchini until flowering.

Squash Vine Borer

Melittia cucurbitae are common in certain areas east of the Rockies.

Squash vine borer, Melittia cucurbitae, is becoming more widespread. The pests occur east of the Rocky Mountains and from Canada to South America. They’re not yet a common problem in the West, but occur in the Midwest, along the East Coast, and particularly in the Southern United States.

Squash vine borer (SVB) is a moth with a bright orange thorax lined with black dots. It flies during the day with a pattern like a wasp’s and a loud buzz. Squash, including zucchini, are hosts, in addition to pumpkins and gourds. 

For only a few plants, it may be feasible to wrap the lower stems to block access. Aluminum foil, burlap, or other materials protect stems from moths trying to lay eggs. The challenge is that they may use another part of the stem or leaf node as entry, rather than the wrapped portion.

BT (Bacillus thuringiensis) is a biological control that stops the caterpillars from feeding. If you’ve scouted and discovered a bore hole or damage, inject liquid BT into the localized section with a syringe. The bacterium at the larval source may work if the borer is still in the vicinity.

BT is only effective against feeding larvae, not eggs or adults, so topical spraying isn’t viable. Spraying also affects the caterpillars and future pollinators we want in our gardens.

Prevention

Using soil to protect the plant could help prevent infestations.

If you live in an SVB-prone area, a preventative measure is to stop growing zucchini, one of the most-impacted cucurbits. Try Cucurbita moschata varieties like ‘Tromboncino.’ While technically a winter squash, it makes a delicious summer squash stand-in when harvested young and green. C. moschata has thick, waxy stems that are more resistant to SVB.

Covering the lower portion of the stem with soil at planting may help reduce infections. The coverage creates a natural barrier, leaving the adult moth unable to access the main stem.

Squash Beetle

They love munching on zucchini leaves.

All these squash-specific insects get confusing, but lastly, we have the squash beetle (Epilachna borealis). Squash beetles feed on cucurbit leaves. The beetles have large black spots on their leaves like lady beetles, and rust-colored wings. 

With squash beetles, you’ll notice chew damage on the leaf surface between the veins. They chew first in a semicircle to carve out their feeding area.

Treatment

Use neem oil if necessary to tackle severe infestations.

Handpick the beetles, larvae (spiny yellow worms), and eggs (orange clusters on the underside of leaves) off the foliage. Use the soapy water bucket disposal method. For larger infestations, neem oil is a treatment option.

Prevention

Covering the seedlings helps protect them.

Clear all debris at season’s end to limit the adults’ overwintering. Lightly tilling the soil surface one or two inches can reduce their winter habitat.

Covered cloches for seedlings prevent early damage by the zucchini pests (remove the covers during flowering).

Spider Mites

These insects gather on the underside of leaves.

Spider mites are sap-sucking zucchini pests that gather on the undersides of leaves. They feed on cellular tissue with piercing mouthparts. Colonies live around leaf veins and mid-ribs beneath leaves. Females lay eggs, and the larvae hatch to feed on sap and tissues. Adults feed and also produce tight webs around leaves, stems, and branches.

Pale spots pop up on leaf surfaces as a result of the feeding, with the foliage showing stippling and bronzing. Leaves stiffen and curl and may prematurely drop. 

Treatment

Ladybugs and other insects are their natural predators.

Beneficial predatory insects like ladybugs, lacewings, and predatory mites help control populations. Spray the leaves and stems with a strong stream of water early in the day to displace the pests.

Prune away affected parts, and dispose of debris rather than adding it to the compost pile. A simple horticultural soap or oil minimizes severe cases.

Prevention

Dry plants in dry environments are more prone to infestations.

Spider mites flock to hot, dry, dusty conditions, and to zucchini experiencing drought stress. Provide even moisture to avoid dry spells and water fluctuations that weaken the crop and make it more susceptible to spider mites.

Aphids

They feed on various plant parts, usually the leaves.

Aphids are soft-bodied sap-feeding zucchini pests that congregate in large numbers underneath leaves. Melon aphids (Aphis gossypii) use cucurbits as hosts. The yellow to green and pear-shaped insects feed on tissues, especially on new shoots.

With an aphid infestation, leaves curl and cup downward before they turn yellow, brown, and drop. Aphids leave behind a sticky honeydew, which often becomes an unattractive black sooty mold in humid conditions. 

Treatment

A strong jet from the hose can displace aphids.

Opt for the same spider mite treatment with a spray of water to displace the insects. Aphids reproduce quickly and in high numbers; if the population is large or damage escalates, an insecticidal soap or oil can be effective.

Prevention

Their natural predators include hoverflies, ladybugs and others.

Start with the best cultural conditions to ward off susceptibility to aphid damage. Ladybugs, hoverflies, and parasitic wasps are the best natural defense that prey on aphid larvae. Interplant diversity of flowering plants in the edible landscape for a well-balanced garden system.

Pickleworms

They dig into buds, stems and other plant parts.

Pickleworms are zucchini pests that impact the fruits and burrow into buds, stems, and flowers. Diaphania nitidalis can severely damage plants at their point of entry, and the fruits rot as a result of burrow holes.

The caterpillars molt four times, changing their color before they pupate and emerge as brownish-yellow moths. The caterpillars begin yellowish-white, turn pink, and finally pale green.

Treatment

Weekly spinosad spraying works well on pickleworm infestations.

Pickleworms usually die out in cold, freezing winters, but they survive in tropical, frost-free climates (like Florida). They migrate north as they emerge, appearing later in the season and damaging the later squash harvests. 

Spinosad sprays in weekly intervals may be effective during pickleworm activity. Apply them as soon as signs of pickleworms appear.

Prevention

Choose zucchini varieties that mature early.

Select early-maturing zucchini like dwarf varieties to miss the height of the feeding population. Compact varieties are often ready before longer vines.

Slugs

They feed on seedlings early in the growing season.

Slugs and snails slide across leaves to feed on soft shoots and tender new growth early in the season. They’re most active in cool, damp conditions in the evening or early morning. You’ll notice irregular holes in leaves and their sluggy trail.

Treatment

DE helps keep soft-bodied insects at bay.

Scout during the most active times to handpick slugs. In the middle of the day, they hide under leaves, mulch, and soil around the base of the vines. Lure them with lettuce leaves or citrus rinds and collect them in the morning.

If numbers increase, bait them with beer or soda traps by filling a shallow dish and placing it at soil level. Remove mulch from around the crop to stave off protective hiding spots.

Diatomaceous earth scattered around the base of the stems contains sharp particles that harm soft-bodied creatures as they crawl. Reapply after heavy rains to maintain the boundary.

Prevention

Strategic irrigation prevents excessively moist conditions.

Target irrigation to reduce damp conditions, which are an inviting habitat for the creatures. Drip irrigation at the base concentrates water directly to the roots without wetting the overall surface area.

Whiteflies

They make the leaves turn yellow and fall off.

Whiteflies are another sapsucking zucchini pest that causes leaves to yellow and drop. Adult whiteflies are tiny and white, and you’ll notice them fluttering around foliage when disturbed.

Adult females lay eggs on leaf undersides, and nymphs hatch to feed on tissues. The adults pierce foliage to feed on sap. 

Treatment

Regularly applying horticultural oil helps address infestations.

Horticultural oils and soaps are treatments in extreme cases, with two applications five days apart.

Remove and destroy leaves in decline. Sticky traps in the vicinity can catch the flyers.

Prevention

Space the seedlings to help maintain airflow and prevent insects from taking over.

Whiteflies most often occur in areas of low airflow. Ensure proper spacing for the crops for ample air circulation around the leafy vines. Grow them vertically on a trellis or other support structure to improve air movement by lifting the vines from the ground level.