Komatsuna

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.

Watch for: 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.

Prevent: 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.

Treat: 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.

The defining pest of this crop, and worse here than on most because komatsuna's summer sowings run straight through the beetles' warm-weather peak. Row cover sealed to the soil from the day of sowing, plus growing the fast summer crops on hard, is what keeps the leaves presentable.

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.

Watch for: 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.

Prevent: 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.

Treat: 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.

Easier to deal with here than on most brassicas: the leaves are smooth with no crinkles to hide colonies, so a hard rinse actually reaches them. The one place they build is deep in the crown at the base of the stalks - check there, and shear a colonized patch back rather than spraying a leaf you eat raw.

Slugs and snails are nocturnal mollusks that rasp ragged holes in soft leaves, shear off seedlings at ground level, and chew into ripe fruit that touches the soil. They feed at night and in the early morning and spend the day hidden under boards, pots, dense mulch, leaf litter, and low foliage, becoming active in exactly the cool, damp, shaded conditions that suit young plants. Damage is heaviest in wet spells and on tender spring growth: a single wet week can erase a row of seedlings while an established, tough-leaved plant of the same species is barely marked. They lay clusters of small pearly eggs in damp soil and under debris, so a garden with plenty of cover carries a resident population year after year rather than being invaded from outside.

Watch for: Irregular ragged holes chewed out of the middle of leaves and along the edges - not the clean-edged cuts a caterpillar leaves. Seedlings that vanish overnight, or that are cut off at soil level with nothing left behind. Silvery dried slime trails across leaves, soil, pots, and paving in the morning: this is the giveaway that tells you it was mollusks rather than an insect. Chewed pits in ripe fruit, especially where it rests on the ground. Damage that shows up on the lowest, dampest leaves first and gets worse after rain or evening watering. Turn over a board, an upturned pot, or a clump of dense mulch during the day and look for the animals themselves sheltering in the cool underneath.

Prevent: Take away the daytime shelter first: lift boards and upturned pots, clear piles of debris, keep dense mulch pulled back from crowns and stems, and give crowded plantings enough airflow to dry out. Water in the morning rather than the evening so the surface is dry by the time they come out. Copper tape around containers and raised beds gives them a shock they will not cross, and it is the one barrier that reliably works. Get plants past the vulnerable stage quickly - start seedlings in pots and set them out at a decent size rather than direct-sowing into a cold wet bed, since most plants stop being worth defending once the leaves toughen. Leave the ground beetles, frogs, toads, and ground-feeding birds alone, because they eat mollusks all night for free and broad-spectrum slug pellets kill them too. Where thick-leaved or resistant varieties exist for what you are growing, they take far less damage.

Treat: Hand-picking works and costs nothing: go out an hour after dark with a headlamp, drop what you find into soapy water, and repeat nightly for a week or two - persistence is what wins, not any single product. Shallow beer traps sunk to soil level catch them too, but need emptying and refilling daily to be worth anything. Iron-phosphate bait is the standard control and is far lower-risk around pets and wildlife than the old metaldehyde products, but it is not harmless: many formulations include EDTA, and a dog that eats a quantity of pellets can develop iron toxicosis. Scatter it thinly per the label, never in piles, and keep dogs off a baited bed. Clear fallen foliage and debris in autumn, where the eggs are laid. In a wet climate this is a population you manage each season rather than one you eradicate - and on most established plants light grazing is cosmetic and needs nothing at all.

A seedling-stage problem: a wet week can erase a newly sown cutting bed, while the upright habit of an established plant keeps most leaves clear of the ground and out of reach. The row cover you are already using against flea beetles blocks them too if the edges are sealed to the soil.

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.

Watch for: 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.

Prevent: 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.

Treat: 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.

Summer sowings sit right in the cabbage whites' season, so this matters more here than on the strictly cool-season Asian greens. The broad flat leaves make caterpillars easy to spot and hand-pick, which on a crop cut every few weeks is usually the whole treatment.

A soil-borne pathogen (Plasmodiophora brassicae) that infects brassica roots and swells them into distorted, clubbed galls. Affected plants stunt and yellow, wilt on warm afternoons and recover overnight, and never size up properly. It is worst in acidic, poorly drained ground, and the resting spores survive in soil for up to 20 years, moving around on soil, tools, boots, water and infected transplants.

Watch for: Midday wilting that recovers overnight, yellowing and stunting with no obvious cause, and - the giveaway - swollen, distorted, clubbed roots instead of clean ones when a plant is pulled.

Prevent: Rotate at least 4 years out of every brassica, counting the fast salad ones and any brassica cover crop. Lime toward pH 7.0-7.2, since the pathogen dislikes alkaline soil, and improve drainage. Plant only clean seed and transplants, never move infested soil or plants around the garden, and grow resistant or tolerant varieties where the disease is known to be present.

Treat: There is no cure once the soil is infested. Pull and destroy affected plants - bag them, do not compost them - lime the bed, and keep brassicas off that ground for years. Rotation and pH are the whole game here.

Komatsuna is Brassica rapa and is infected as readily as cabbage or turnip. Because it is fast enough to crop three seasons a year, the real risk is resowing the same bed over and over - rotate successions to different ground rather than building spore load in one spot.

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.

Watch for: 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.

Prevent: 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.

Treat: 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.

Mostly a cool wet spring problem, and this crop is usually fast enough to outrun it. The row cover you already have on against flea beetles blocks the egg-laying fly as well, provided the edges are sealed to the soil.