Kale

Tough kale keeps producing through a fair amount of chewing, so this is rarely worth spraying. Curly and savoyed types hide worms in the crinkles - look into the folds and along the growing point, and give leaves a good rinse before eating them raw.

Ragged holes in the leaves, dark-green frass in the crown, and green caterpillars that match the leaf and hide along midribs and leaf undersides. White butterflies fluttering low over the bed mean eggs are going down now - look under the leaves for the small pale-yellow eggs, laid one at a time rather than in clusters.

Bt (Bacillus thuringiensis kurstaki) is the one to reach for first: it affects only caterpillars and is safe around bees, parasitic wasps, and hoverflies. Spinosad also works, but it is not caterpillar-specific - while the spray is still wet it is toxic to bees and to the parasitic wasps that hunt cabbage worms for you. If you use it, spray at dusk so it dries before bees are out, and never wet open flowers, including flowering companions like dill or nasturtium. Follow the label for both. On a small planting, hand-picking and rubbing off eggs is enough on its own.

Floating row cover from sowing or transplant is the near-complete fix - it stops the adults ever laying. Seal it at the soil edges and lift it only to weed or harvest. Otherwise check leaf undersides twice a week, rub off the eggs, and hand-pick the caterpillars. Let dill, cilantro, or other umbels flower nearby to feed the parasitic wasps that do this work for you.

The brassica caterpillar complex: velvety green imported cabbageworms (larvae of the white cabbage butterfly) and inch-worming cabbage loopers (a moth larva). Both chew large ragged holes through the leaves, then work into whatever folds up at the center - head, curd, sprout, or growing crown - fouling it with green pellet droppings. Fast leaf crops are usually cut before the damage matters; slow heading crops suffer most. Nasturtium carries the same mustard-oil chemistry that cues the butterflies to lay, so it hosts them too and is often planted nearby as a decoy.

Bright orange-and-black shield bugs on leaves and stems, whitish or yellow cloudy stippling and wilting, and barrel-shaped black-and-white striped eggs standing in rows on leaf undersides.

Hand-pick the conspicuous adults into soapy water and crush egg rows; insecticidal soap or spinosad on heavy nymph populations. Spinosad is acutely toxic to bees while the spray is wet - apply at dusk when bees are not flying, never to plants in flower, and follow the product label.

Clean up brassica and cruciferous-weed debris where adults overwinter; row cover young plants; handpick early-season adults before they breed.

A shield-shaped stink bug boldly patterned in orange/red and black that sucks sap from mustard leaves, leaving pale cloudy blotches and wilting. A major pest of leafy brassicas in warm regions, and mustard is a preferred host - which also makes it a useful trap crop.

Kale usually survives an attack and keeps producing, but a checked plant stays small all season. Spring sowings are the ones at risk; fall kale largely escapes it.

Sudden wilting on the first warm days even though the soil is moist, stunted plants with a bluish cast, and - on pulling a failing plant - brown tunnels and slimy scarring through the roots with small white maggots inside.

There is no rescue once the maggots are inside the roots. Pull and destroy badly infested plants rather than composting them, and reset the bed with row cover and rotation. Beneficial nematodes drenched into the soil help suppress the larvae in a bed you have to keep using.

Cover the crop with floating row fabric from the day you sow or transplant, sealing the edges down to the soil so the fly cannot reach the stems, or fit a cardboard or felt collar disc flat around each stem to block egg-laying. Rotate at least three years away from ground that grew brassicas, and do not plant into fresh manure.

The larvae of a small gray fly that lays its eggs at the soil line against brassica stems. The white maggots hatch and tunnel down into the roots, scarring and rotting them, so plants wilt on warm days, stunt, take on a blue-green cast, and can die outright; root brassicas are tunneled through and spoiled. It is worst in cool, wet spring soil, on transplants and early sowings, and in ground that grew brassicas the year before.

Mostly a threat to seedlings; mature kale outgrows them. Because the leaf is the crop, mesh over young plants is worth it if you want unblemished leaves.

Dozens of pinhead-sized round holes peppered across the leaves, thickest on the youngest, most tender growth. Tiny beetles that spring away as you brush the plants or lean in for a closer look - that jump is the identification. Seedlings that go lacy and stop growing, and transplants that sit and sulk instead of taking off. Damage heaviest in warm, dry weather and along the edge of a bed nearest weedy ground or last year's crop debris. On root crops, shallow narrow grooves or channels scarring the skin at harvest, from larvae feeding underground.

Row cover and healthy fast growth carry most crops through, and on an established plant the damage is usually cosmetic and needs nothing at all. Where a young planting is genuinely being stripped, kaolin clay coats the leaves and deters feeding, and spinosad will knock the beetles back. Spinosad is acutely toxic to bees while the spray is still wet - apply it at dusk when bees are not flying, never onto plants in flower, and follow the product label. Anything you spray must be labeled for the plant you are treating, and you must observe its pre-harvest interval on a crop you are picking. Yellow sticky traps are useful for telling you when the beetles have arrived. Where the damage falls on the part you eat, harvesting young often beats them outright; where you are growing for a root or a fruit, leaf damage can simply be tolerated. Larvae feeding underground cannot be reached by a foliar spray, so rotation and clean beds are what work against those.

Floating row cover or fine insect mesh, laid over the bed from the day of sowing or transplanting and sealed at the edges so nothing can walk in underneath, is the single best defense - and on the crops they favor it is close to essential. Leave it on until plants are large and growing strongly, or until flowering on anything that needs pollinating. Push growth: a well-watered, unchecked plant outgrows the damage, so the whole game is getting seedlings through their vulnerable weeks fast. Keep beds weed-free, since related weeds host the beetles alongside your crop, and clear crop debris at the end of the season where the adults overwinter. Rotate away from a bed that grew a related crop last year. Where you can, shift sowing dates - cooler-season and fall plantings often miss the peak of adult feeding entirely.

Flea beetles are tiny dark beetles - often shiny black or bronze, rarely more than a couple of millimeters long - with enlarged back legs that let them spring away like fleas the moment you lean in. The adults chew countless small round pits and shot-holes through leaves, giving the foliage a peppered, buckshot-riddled look. They overwinter as adults in leaf litter, hedgerows, and crop debris, emerge hungry in spring, and are worst in warm dry spells. The damage is mostly a seedling and transplant problem: a small plant with a few leaves can be checked, stunted, or killed outright, while the same plant shrugs them off once it is large and growing strongly. Different species specialize on different plant families, so the beetles hammering your brassicas are not the ones on your nightshades. Some species also have larvae that feed on roots and tubers underground.

Kale is picked leaf by leaf over months, which means repeated handling - do it only when the foliage is dry, or you will carry the bacterium down the row yourself.

Yellow V-shaped wedges opening inward from the leaf margins, with darkened, blackened veins running through the wedge - the combination is diagnostic. Leaves yellow and drop, and a foul soft rot advances toward the stem, head or curd.

There is no cure. Remove and destroy infected plants - never compost them - disinfect tools between plants, do not save seed from an infected crop, and keep brassicas out of that ground for years. Clean seed and rotation are the whole strategy.

Start with clean, hot-water-treated seed, since the bacterium travels on seed. Rotate at least three years out of brassicas, space plants widely for airflow, water at the base rather than overhead, never work or harvest the plants while the leaves are wet, and control cruciferous weeds, which host it between crops.

The most serious bacterial disease of brassicas (Xanthomonas campestris), and it thrives in warm, wet weather. It enters at the leaf margins through the pores and through wounds, then moves inward along the veins, producing yellow V-shaped wedges pointing in from the leaf edge with blackened veins inside them. From there it works into the stem and head as a foul soft rot. It is seed-borne as well as soil- and debris-borne, and it spreads readily on hands, tools and splashing water when plants are worked while wet.