Winter Squash

The melon aphid spreads mosaic viruses that can mottle leaves and warp fruit; watch new growth for curling.

Dense clusters of tiny insects packed onto shoot tips, flower buds, and the undersides of young leaves. Curled, cupped, or distorted new growth that never opens properly. A sticky shine on the leaves - and on whatever sits under the plant - that later goes black with sooty mold. Tiny white cast skins left behind where a colony has been feeding. Ants running steadily up and down the stems, which is often the first thing you notice. Mottled, streaked, or misshapen leaves that do not grow out can mean a virus the aphids brought with them rather than the feeding itself.

Knock the colonies off with a hard jet of water and repeat every few days - on most plants that alone ends it. Pinch out or prune off the worst-infested tips rather than treating the whole plant. If colonies keep rebuilding, spray insecticidal soap or horticultural oil directly onto the insects, covering leaf undersides, and repeat weekly until they are gone; treat early or late in the day, and never spray a wilted or heat-stressed plant. Avoid broad-spectrum insecticides - they kill the ladybugs, lacewings, and parasitic wasps that were about to solve the problem for you, and aphid numbers usually come back worse afterward. Anything you spray must be labeled for the plant you are treating; follow that label and observe its pre-harvest interval. On anything you eat, wash leaves, heads, and buds well before use, since aphids hide down in crowns, folds, and tight growth.

Go easy on nitrogen: the soft, lush growth that heavy feeding produces is exactly what aphids breed on. Check new growth once a week through spring and early summer so you catch colonies while they are still small, and rub the first few out with your fingers. Leave flowering plants nearby and skip broad-spectrum sprays - ladybugs, lacewings, hoverflies, and parasitic wasps do most of this work for free, and they only stay if there is something for them to eat. Keep ants off the plant where you can, since they protect aphids from those predators. Water steadily so plants are not stressed, and check any new plant over before you bring it home or move it indoors, since aphids usually arrive on something else.

Aphids are small soft-bodied sap-suckers - green, black, gray, pink, or waxy white, and mostly wingless - that gather in dense colonies on the tenderest new growth: shoot tips, buds, and the undersides of young leaves. They breed extremely fast in mild weather, so a few can become hundreds inside a week. Their feeding curls and distorts soft growth, and the sticky honeydew they excrete coats everything below and turns black with sooty mold. Ants often farm and defend the colonies for that honeydew. A few aphids are normal on almost any plant and a healthy plant shrugs them off; only dense, persistent colonies do real damage, and some aphids also spread plant viruses as they feed.

Damages seedlings and scars the rind; winter squash tolerates the bacterial wilt they spread better than cucumbers and melons do.

Ragged holes in leaves and flowers, scarred fruit rind, and the beetles themselves - striped or spotted, about a quarter inch - diving into blossoms as you approach.

Hand-pick in the cool early morning when beetles are sluggish; kaolin clay deters feeding; spot-treat heavy pressure at flowering with an evening insecticide application to spare bees. Use only a product labeled for the crop you are treating, follow the label exactly, and observe the pre-harvest interval before you pick. Controlling beetles is really about preventing the wilt they spread.

Row covers from planting until flowering are the single best defense (remove at bloom for pollination); yellow sticky traps; delay-sow past the first beetle surge; clean up crop debris in fall and choose wilt-tolerant varieties.

Small yellow beetles marked with black stripes or spots that chew leaves, flowers, and fruit rind. Their real danger is disease: they carry and spread the bacterium that causes cucurbit bacterial wilt and also transmit mosaic viruses, so even light feeding can be costly.

Winter squash is less susceptible than cucumber or melon; a wilting vine is more often the borer, so check the stem base for frass first.

Individual runners wilting in midday sun and reviving at night, then whole-plant collapse; a cut wilted stem oozes sticky sap that strings into a fine thread when you touch it and pull away.

None - remove and destroy wilting plants before beetles carry the bacteria to healthy vines. Prevention through beetle management is the only real control.

There is no cure, so the whole strategy is beetle control: row covers until flowering, prompt beetle knockdown, and wilt-tolerant varieties. Cucumber beetles carry the bacterium over winter and infect through feeding wounds.

A bacterial disease (Erwinia tracheiphila) spread by cucumber beetles that plugs the plant's water-conducting vessels. Infected vines wilt in the heat, recover overnight at first, then collapse and die. Cucumbers and muskmelons are most susceptible; watermelon is essentially immune.

Squash is less hard-hit than cucumber, but a wet summer that strips the leaves early leaves fruit poorly filled and less storable.

Angular yellow blotches on the upper leaf surface bounded by the veins (a blocky, mosaic look), with a gray-purple fuzzy growth on the underside in morning humidity; leaves brown and die from the oldest inward.

Remove affected leaves early and harvest ahead of a wet forecast; protectant copper or approved fungicides slow it if applied before infection takes hold. Once established in warm, humid weather it moves faster than sprays can keep up.

Grow resistant varieties; maximize airflow and sun; water at the base early so leaves dry fast; and watch the regional downy-mildew forecast maps that track the disease moving north each summer.

A fast-moving, wind-borne water mold (Pseudoperonospora cubensis) specific to the cucurbit family. Cool, wet, humid weather triggers it, and it can defoliate a planting within a week or two. Unlike powdery mildew it needs leaf moisture to spread.