Radish

Radish roots are tunneled and scarred brown, which spoils them outright rather than merely checking growth. Early spring sowings into cold wet ground are the worst; row cover from the day you sow is effectively the whole answer.

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.

A top radish pest, because they hammer the brassica foliage. The fast radish crop usually outgrows light feeding under row cover; sow early or in cooler weather, and rotate away from brassica beds.

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.