Pests
Symptoms Lots of tiny round shot holes peppering the leaves, made by tiny dark beetles that jump like fleas when you come near. Bok choy is one of their very favorite plants, and heavy damage can riddle or kill young seedlings.Small round shotholes pepper the foliage and the tiny dark beetles jump when disturbed. Bok choy and other mustards are highly preferred hosts, so pressure is often intense; seedlings can be stunted or killed and the holes mar the leaf-stalks of a crop eaten raw or lightly cooked. Cause Flea beetles are small jumping beetles that chew little pits and holes in cabbage-family leaves. They are drawn strongly to bok choy and mustards and hit small seedlings hardest, since a tiny plant cannot outgrow the damage.Crucifer flea beetles (Phyllotreta species) chew the foliage of brassicas and strongly prefer bok choy and mustard; adults overwinter in debris and emerge to attack the earliest, smallest plants, with multiple generations through the season. Organic treatment Cover young plants with a light row cover from the day you sow, and if beetles are heavy use a spinosad spray. The main goal is to get the seedlings up and growing fast, before the beetles riddle them.Floating row cover from sowing is the most effective tool; spinosad helps under heavy pressure. The aim is rapid establishment past the vulnerable seedling stage, so push fast growth. Prevention Use row cover from sowing, the single best defense, keep seedlings growing fast with steady water, and clear nearby cabbage-family weeds. Some growers plant a sacrificial mustard patch as a trap crop.Exclude beetles with row cover from sowing, keep seedlings vigorous with even water and a light feed, clean up crucifer weeds and crop debris, and consider an early trap planting of mustard to divert beetles from the main crop.
Symptoms Clusters of small gray-green insects with a dusty, waxy coating on the new growth and tucked deep into the folds where the leaf-stalks meet, where they are very hard to wash out. Leaves may curl and there can be a sticky film.The gray-green, waxy-coated cabbage aphid forms dense colonies on growing tips and leaf undersides and lodges deep in the leaf-stalk folds, where it contaminates the harvested plant with insects and honeydew and is very hard to clean. Clemson notes aphid feeding yellows, stunts, curls, and wrinkles the foliage and brings sooty mold, with pressure heaviest on the fall crop. Cause Cabbage aphids are tiny insects that suck the plant's juices and breed fast. They love cabbage-family plants and hide down in the stalk crevices, which is the part you eat.Brevicoryne brassicae, a brassica-specialist aphid (with green peach aphid also present), sucks sap and reproduces rapidly; contamination of the harvested stalks with aphids and sticky honeydew is usually the real problem rather than plant stunting. Organic treatment Knock colonies off with a strong spray of water and hit the undersides of leaves and the crevices with insecticidal soap or neem oil, repeating every few days. Welcome ladybugs and lacewings, which eat aphids.Dislodge colonies with a strong jet of water and spray insecticidal soap, neem, or horticultural oil with thorough coverage of leaf undersides and the stalk crevices; repeat every few days. Conserve natural enemies (parasitoid wasps, hoverflies, ladybugs). Prevention Check the growing center and the stalk crevices often and act early. Go easy on nitrogen, since soft growth draws them, use row cover, and clear away old cabbage-family plants after harvest.Scout growing tips and the stalk crevices weekly and catch infestations before aphids lodge in the plant. Avoid excess nitrogen, use row cover on young plants, and destroy crop debris that carries them over.
Symptoms Ragged chewed holes in the leaves, green caterpillars on the plants, and dark droppings. Because you eat the leaves and stalks, even a little chewing and mess is a problem.Ragged feeding holes with green or striped larvae and frass; the imported cabbageworm, cabbage looper, and diamondback moth larvae feed on bok choy (UMN lists all three), and on a fast leaf-and-stalk crop even light feeding and contamination downgrade the harvest. Cause Several white butterflies and moths lay eggs on cabbage-family leaves, and the caterpillars that hatch (imported cabbageworms, loopers, and small wriggling diamondback larvae) chew the foliage.The larvae of several brassica moths and butterflies feed on the foliage; the adults lay eggs on the leaves, and warm-region plantings see the most pressure. The diamondback moth is often the most numerous in the South. Organic treatment Spray Bt, which is safe and targets only caterpillars, or pick them and their eggs off by hand from the undersides of leaves. Spray again after rain, since it washes off.Apply Bt (Bacillus thuringiensis kurstaki) or spinosad targeting young larvae and hand-pick where practical; repeat after rain, since Bt breaks down. Prevention Use a row cover to keep the adults from laying eggs, clean up old cabbage-family plants and weeds, and check leaf undersides for eggs and small caterpillars.Exclude egg-laying adults with row cover, clean up brassica debris and weed hosts, and scout leaf undersides for eggs and early instars.
Symptoms New transplants wilt and grow badly or fall over. If you pull one up, you'll find small white maggots eating the roots. It is worst in cool, wet spring soil.Transplants wilt, grow poorly, and may collapse; pulling a plant reveals small white maggots tunneling in the roots and lower stem. Damage is worst in cool, wet soil at spring establishment (UMN lists cabbage maggots among bok choy's pests). Cause A small fly lays eggs at the base of the plant, and the maggots that hatch burrow down and eat the roots. The fly is most active in cool, damp weather, so spring transplants are most at risk.The larvae of the cabbage root fly (Delia radicum) tunnel into brassica roots; the adult lays eggs at the stem base, and the maggots feed below, sometimes killing young plants and opening the door to rots. Organic treatment Once the maggots are in the roots you can't save that plant, so pull and throw away the badly damaged ones. Put your effort into protecting the rest from new eggs.There is no effective rescue once maggots are in the roots; remove and destroy badly affected plants and protect the rest from further egg-laying. Prevention Put a small collar or disk around the base of each transplant to stop the fly from laying eggs there, or use a row cover. Avoid planting into cold, soggy soil, and rotate away from where cabbage-family plants grew.Place a collar or disk around the stem base at transplanting to block egg-laying, or use row cover; avoid planting into cold, wet soil and rotate away from where brassicas grew.
Symptoms Shield-shaped black-and-orange (or black-and-red) bugs on the leaves, which develop pale spots, then brown and look tattered. It is mostly a warm-region problem and loves cabbage-family plants.Shield-shaped bugs brightly marked black-and-orange or black-and-red feed with piercing-sucking mouthparts that leave pale stipples; affected leaves brown and look tattered, and heavy feeding wilts and deforms plants. A warm-region brassica specialist (Clemson). Cause The harlequin bug is a colorful stink-bug relative that pierces the leaves and sucks the juices, leaving pale blotches. It strongly prefers cabbage-family plants, especially in the South.The harlequin bug (Murgantia histrionica) specializes on cole crops, most damaging in the southern United States, where it completes several generations a year and overwinters as an adult in debris and weeds. Organic treatment Search out and crush the bugs, their barrel-shaped eggs laid in rows, and the young ones by hand. Use a row cover to keep them off, pull badly infested plants, and clear away weeds and old plants where they hide over winter.Hand-pick and crush adults, nymphs, and the barrel-shaped egg rows; exclude with floating row cover; remove heavily infested plants. Insecticidal soap or neem helps where pressure is severe. Prevention Clean up garden debris and cabbage-family weeds where the adults overwinter, use row cover, and consider a trap crop of mustard to lure them away from the main crop, then destroy it.Eliminate overwintering sites by removing crop debris and crucifer weeds, use row cover, and deploy an early trap crop of mustard to divert overwintering adults, then destroy it before the main crop is set out.
Symptoms Ragged holes with smooth edges chewed in the low leaves and stalks, slimy trails on the plant and soil, and worst damage in cool, damp, shady spots and after rain.Smooth-edged holes in low foliage and tender stalks with silvery slime trails, worst in cool, wet, densely planted or heavily mulched beds; a succulent low green like bok choy is highly susceptible (NCSU lists slugs and snails). Cause Slugs and snails are soft, moisture-loving mollusks that feed at night and rasp holes in tender low greens like bok choy. They thrive in damp mulch and dense, shaded plantings.Several slug and snail species feed nocturnally, rasping the foliage; they shelter in moist debris and mulch by day and build up in cool, wet conditions. Organic treatment Hand-pick at night or after rain, set out shallow traps, and use an iron-phosphate slug bait, which is pet-safe. Reduce damp hiding places and water in the morning so the surface dries by night.Hand-pick after dark or rain, use shallow traps and iron-phosphate baits (pet-safe), and remove daytime shelter; morning watering lets the surface dry before they feed. Prevention Thin and space plants for airflow, keep mulch light near the plants, clear damp debris, and water early in the day rather than at dusk.Reduce moisture and shelter near the plants: thin for airflow, keep mulch off the crowns, clear debris, and irrigate in the morning rather than the evening.
Diseases
Symptoms Plants wilt in the afternoon, stay small and yellowish, and don't bounce back. If you dig one up, the roots are swollen into lumpy, club-shaped knobs.Plants wilt in the heat of the day, grow stunted and yellowed, and recover poorly; roots are swollen into distorted clubs and galls instead of normal fine roots. Cause A germ that lives in the soil infects the roots of cabbage-family plants and makes them swell, which stops the plant from taking up water and food. It stays in the soil for years.A soilborne organism (Plasmodiophora brassicae) infects brassica roots and forms the galls, which block water and nutrient uptake. It persists in soil for many years, spreads in contaminated soil and water, and infects most readily in acidic soils below about pH 6.5. Organic treatment There's no cure once a plant has it, so pull and destroy infected plants. Keeping the soil from being too acidic (closer to neutral) helps hold it back, and growing cabbage-family plants only rarely in that spot starves the germ out.There is no cure once plants are infected; remove and destroy them. Raising soil pH toward neutral with lime suppresses the disease, and long rotations starve it out over time. Prevention Don't grow bok choy or other cabbage-family plants in the same spot more than once every few years, longer if you've had clubroot. Keep the soil from being too acidic, improve drainage, and clean soil off your tools.Rotate brassicas out of affected ground on a long cycle (UMN advises up to 7 years where clubroot is known), keep soil pH up, improve drainage, and avoid moving infested soil on tools and boots.
Symptoms Pale yellow blotches on top of the leaves, with fuzzy grayish growth on the underside, mostly in cool, damp weather. Bad cases discolor and spot the leaves and stalks.Pale yellow patches form on the upper leaf surface with a fuzzy gray-white growth underneath, mainly in cool, damp weather; severe infection discolors and spots the leaves and stalks. Bok choy's cool, humid season overlaps the weather it likes. Cause A mold-like disease that loves the cool, wet weather bok choy grows in, spreading through wet leaves and splashing water. Crowded plants and long leaf wetness make it worse.A fungus-like organism (Hyaloperonospora brassicae) that thrives in cool, wet, humid conditions and spreads by spores in water and air; long leaf wetness and crowded plantings favor it (Clemson). Organic treatment Open up the airflow so leaves can dry, remove the worst leaves, and water at the soil instead of from above. It's hard to stop once the weather stays damp, so prevention matters most.Improve airflow and let foliage dry, remove badly affected leaves, and apply a copper-based fungicide if pressure is high; the disease is hard to stop once humidity stays high. Prevention Space plants so air moves between them, water at the soil line, and pick resistant varieties if downy mildew is common where you live.Space plants for good air movement, water at the soil line rather than overhead, and choose resistant varieties where downy mildew is common.
Symptoms Yellow patches shaped like the letter V appear at the leaf edges, pointing inward, with black veins inside them. It can spread through the plant and rot it.Yellow, V-shaped lesions spread inward from the leaf margins, with the veins inside the V turning black (Clemson); the disease moves through the vascular system and can rot the plant. Often the most serious brassica disease in warm, wet weather, and UMN lists it among bok choy's diseases. Cause A bacteria that often comes in on infected seeds or transplants. It gets into the leaves and travels through the plant's veins, spreading fastest in warm, wet weather.A seedborne bacterium (Xanthomonas campestris pv. campestris) that enters through leaf pores and wounds and moves through the veins; it spreads in warm, wet conditions and on infected seed or transplants. Organic treatment There's no real cure, so remove and destroy infected plants to keep it from spreading. Don't handle or brush against the plants while they're wet, because that spreads the bacteria.There is no effective cure; remove and destroy infected plants. Avoid working among plants when foliage is wet, since that moves the bacteria. Prevention Begin with clean, certified seed and healthy transplants, don't plant where cabbage-family crops grew recently, space plants for airflow, and avoid overhead watering.Start with clean, certified seed and healthy transplants (a hot-water seed treatment helps), rotate 2 to 3 years away from brassicas, give plants room for airflow, and avoid overhead watering and handling wet foliage.
Symptoms Small dark spots on the leaves that grow into round patches, often with rings like a tiny target. Bok choy is especially prone to it, and spotted leaves are not good to eat.Brown circular leaf spots with characteristic concentric rings (target spots) that enlarge and coalesce (Clemson); on a leaf crop even moderate spotting downgrades the harvest. Clemson notes Chinese cabbage and bok choy are more susceptible to Alternaria than common cabbage, and UMN lists it among bok choy's diseases. Cause A fungus that spreads in warm, wet weather and infects the leaves, leaving spots. It is worse on crowded, damp plantings and comes in on infected seed.Alternaria fungi (A. brassicicola, A. brassicae) infect brassica foliage, spreading by spores in wind and splashing water; infected seed, crop debris, and long leaf wetness drive them. Organic treatment Remove and destroy spotted leaves and old plant debris, improve airflow so leaves dry quickly, and avoid wetting the leaves when you water. Start with clean seed.Remove spotted leaves and crop debris immediately, improve airflow, and avoid overhead watering; a copper-based fungicide can help under heavy pressure. Prevention Use clean seed, rotate away from brassicas, space plants for airflow, water at the soil line, and clear crop debris after harvest.Use clean, disease-free seed, rotate away from brassicas, space for airflow, water at the soil line, and clear crop debris that harbors spores after harvest.
Symptoms White, blister-like bumps on the undersides of the leaves, with yellow spots on top. Badly spotted leaves are not good to eat.White, blister-like pustules on leaf undersides with chlorotic spotting above; severe infection distorts and downgrades the foliage. A common brassica-greens disease, listed among bok choy's problems by NCSU and worse in mild, moist conditions. Cause A mold-like disease, not a true rust, that makes white pustules on cabbage-family leaves and spreads in cool, moist weather. It can ruin a leafy crop quickly.The oomycete Albugo candida, favored by cool nights, mild days, and leaf wetness; it spreads by splash- and wind-dispersed spores and survives on debris and as oospores. Organic treatment Remove and destroy infected leaves, improve airflow, and water at the soil line. As with downy mildew, prevention works better than trying to cure it.Remove infected leaves and debris, improve airflow, and avoid overhead irrigation; chemical options are limited for the home garden. Prevention Space plants out, avoid wetting the leaves, choose resistant varieties where it is common, and rotate your planting spot.Grow resistant cultivars where white rust is endemic, space for airflow, use drip irrigation, and rotate away from brassicas.
