Summer Squash

Squash bugs love summer squash; scout leaf undersides for egg clusters twice a week from the seedling stage.

Neat bronze egg clusters in the V of leaf veins on the undersides, fast-moving gray nymphs, and adults that scatter when you lift a leaf or a board laid nearby.

Hand-pick adults and crush egg clusters daily - this alone controls small plantings. Target young nymphs with insecticidal soap or neem; mature adults shrug off most sprays, so timing on the nymph stage is everything. Use only a product labeled for the crop you are treating, follow the label exactly, and observe the pre-harvest interval before you pick.

Scrape egg masses off leaves into soapy water; clear old vines and mulch that shelter overwintering adults; lay a board at dusk and destroy the bugs that gather beneath it by morning; row covers until bloom.

Flat, gray-brown shield-shaped bugs that pierce leaves and stems to suck sap, injecting a toxin that wilts and browns foliage. Adults and gray nymphs cluster at the plant base and can overwhelm young plants; they are hardest to kill once mature.

One of summer squash's most destructive pests - a July succession sowing that matures after the moth flight is the surest home-garden defense.

Sudden wilting of a whole vine in midsummer, a small hole near the stem base oozing wet, sawdust-like frass, and orange-and-black moths flying by day.

At the first frass, slit the stem lengthwise, dig out and destroy the grub, then bury that stem section in moist soil to re-root. Bury vine nodes along the row so the plant survives even if the crown is lost. Destroy spent vines in fall.

Cover young plants with row fabric until flowering (remove for pollination); wrap or mound soil over the lower stem to block egg-laying; plant a second sowing in early July after the moth's main flight; grow resistant Cucurbita moschata types where borers are severe.

The larva of a clearwing moth that looks like a wasp. The moth lays eggs at the base of stems in early summer; the grub tunnels inside and hollows the vine, cutting off water so the plant wilts and collapses seemingly overnight. Squash and pumpkins are the favored hosts.

Nearly universal on summer squash by late season. A July succession sowing gives you clean young plants just as the first ones mildew out, which is far more reliable than trying to hold an infected planting together.

Round white powdery spots on the upper leaf surfaces that spread and merge until whole leaves look dusted. It usually starts on the oldest, lowest, most shaded leaves and works upward, so check there first. Look at the undersides too, and at stems, buds, and flower stalks, which get coated as it advances. Leaves that yellow, brown, curl, or go crisp and drop early under the coating. New growth that opens small, crumpled, or twisted where the fungus has reached the shoot tips. On plants where it gets onto the fruit, a dull gray film, russeted or scarred skin, and cracking. Late in the season, tiny dark specks scattered through the white felt - that is the fungus setting up to overwinter on the debris.

Start early: sprays protect healthy tissue, they do not clean up leaves that are already coated. Pick off and bin the worst leaves as soon as you see them, and open the plant up by thinning or pruning so air moves through. On anything that regrows quickly, shearing the whole plant back forces a clean flush and beats spraying. If it keeps spreading, potassium bicarbonate, horticultural oil, or neem applied weekly will hold it - cover both leaf surfaces. Sulfur also works, but it burns the foliage of some plants, should never go on in heat, and must not be mixed with or applied close behind an oil spray. Whatever you use must be labeled for the plant you are treating: follow that label and observe its pre-harvest interval on anything you eat. Do not compost badly infected material. Late-season mildew on a plant that is finishing anyway is usually cosmetic; on a crop still filling out it is worth acting on.

Give plants room. Crowding and still air are the biggest single driver, so space at the full recommended distance, thin seedlings properly, and divide or prune out congested growth until air moves through the plant. Full sun and an open position help; deep shade and a still corner against a wall are where it always starts. Water at the base rather than overhead, and water early in the day so nothing stays damp overnight. Keep plants evenly watered - drought stress at the roots leaves them far more susceptible, even though the fungus itself likes dry air. Go easy on nitrogen, since soft lush growth is the most vulnerable. Where resistant varieties exist for what you are growing, choosing one is the single most effective thing you can do on a plant that mildews every year. Clear infected leaves and stems away at the end of the season rather than composting them.

Powdery mildew is a fungal disease that coats leaves - and often stems, buds, and fruit - in a white-to-gray powder that looks like spilled talcum. It is not one fungus but a large family of them, each fairly specialised to its own group of plants, which is why mildew on one crop rarely jumps to an unrelated one beside it. Unlike most leaf diseases it does not need wet leaves: it thrives on warm dry days followed by humid nights, and it takes hold fastest where plants stand crowded in still air or in shade. The coating blocks light, so heavily covered leaves yellow, brown, and drop early. On many plants that is mostly disfiguring and arrives late enough not to matter; where it strips away the leaves a crop still needed to finish, it costs you size, sweetness, and quality.