Pests
Symptoms You'll see clusters of small gray-green insects with a dusty, waxy coating on the new growth and, worst of all, packed down inside the developing sprouts 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 is the signature brussels sprouts pest. Colonies build on growing tips and leaf undersides and then lodge deep inside the developing sprouts, where they contaminate the marketable buds with insects and honeydew and are extremely hard to clean at harvest. Populations explode on the long-season late-summer and fall crop. Cause Cabbage aphids are tiny insects that suck the plant's juices and breed fast, especially on the long-season fall crop. They love brussels sprouts and hide right inside the little sprouts, which is the part you eat.Brevicoryne brassicae, a brassica-specialist aphid, sucks sap and reproduces rapidly; on brussels sprouts it feeds in the upper leaves, flower buds, and especially within the forming sprouts. Contamination of the harvested sprouts 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 into the sprouts 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 into the sprouts; repeat every few days. Conserve natural enemies (the parasitoid Diaeretiella rapae, hoverflies, ladybugs) that suppress this aphid. Prevention Check the growing tips and sprouts often and act early, before the aphids get down into the sprouts. Go easy on nitrogen fertilizer once sprouts form, since soft growth draws them, and clear away old cabbage-family plants after harvest.Scout growing tips and the leaf axils weekly and catch infestations before aphids colonize the sprouts. Avoid excess nitrogen once sprouts set (soft growth favors them), use reflective mulch or row cover on young plants, and destroy crop debris that carries them over.
Symptoms You'll see ragged holes chewed in the leaves, green caterpillars on the plant, and dark droppings, and later the caterpillars may bore into the sprouts. Some loop up in the middle as they crawl.Ragged holes chewed in the leaves with green caterpillars and dark frass; as the season goes on, larvae also bore into the sprouts and foul them. Imported cabbageworms are velvety green; cabbage loopers move in a looping arch; diamondback larvae are small and wriggle when disturbed; the cross-striped cabbageworm shows black and white bands. Cause These are caterpillars that hatch from eggs laid by white butterflies and small moths. They love cabbage-family plants and chew the leaves, and they can tunnel into the sprouts you want to eat.The larvae of the imported cabbageworm, cabbage looper, and diamondback moth (Clemson rates the diamondback the most numerous in home gardens) feed on brassica foliage and contaminate the sprouts; the adults are white or brownish butterflies and moths that lay eggs on the leaves. Organic treatment Spray Bt, which is safe and targets only caterpillars, or spinosad, and pick caterpillars and eggs off by hand from under the leaves. Spray again after rain, since it washes off.Spray Bt (Bacillus thuringiensis kurstaki) or spinosad, which target caterpillars and spare beneficials, and hand-pick larvae and eggs from leaf undersides. Repeat after rain, since Bt breaks down. Prevention Cover plants with a light fabric row cover after planting to keep the butterflies and moths from laying eggs, clear away old cabbage-family plants, and watch for the first white butterflies as your signal to act.Use floating row cover or fine mesh from transplanting to exclude the egg-laying adults, clean up brassica debris that shelters pupae, and scout for the first white butterflies as a spray cue. Tighten control once sprouts begin forming, since damage to the buds is the costly kind.
Symptoms Shield-shaped black-and-orange (or black-and-red) bugs on the leaves, which develop white or yellow spots, then brown and look tattered. It is mostly a warm-region problem and loves cabbage-family plants.Shield-shaped bugs up to about 3/8 inch, brightly black-and-yellow or black-and-red, feeding with piercing-sucking mouthparts that leave white stipples; affected leaves brown and look tattered, and heavy feeding wilts and deforms plants. A warm-region brassica specialist. 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) is a true bug that specializes on cole crops, most damaging in the southern United States, where it completes two to three 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, pyrethrum, or neem help 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 cleome or 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 cleome or mustard to divert overwintering adults, then destroy it before the main crop is set out.
Symptoms Lots of tiny round holes in the leaves of young plants, made by small dark beetles that jump away like fleas when you get close. Bad damage can stunt seedlings.Tiny round shot-hole pits chewed in the leaves of young plants; the small dark beetles jump like fleas when disturbed. Heavy feeding stunts or kills seedlings and slows establishment of the long-season crop. Cause Flea beetles are small jumping beetles that chew on young cabbage-family leaves. They hurt seedlings most, because a tiny plant can't grow fast enough to recover.Flea beetles chew the foliage of young brassicas and are most damaging at the seedling stage; a vigorous transplant generally outgrows them, but a stalled seedling can be set back badly. Organic treatment Cover young plants with a row cover, and if there are a lot of beetles, use a spray such as spinosad. The main goal is to get the seedlings big enough to handle the damage.Protect seedlings with row cover and spray spinosad if pressure is high; the goal is getting plants past the vulnerable seedling stage. Prevention Cover seedlings with row cover from the start, keep them strong with steady water and food so they grow past the damage, and pull nearby weeds in the cabbage family.Use row cover from transplanting, keep seedlings vigorous with even water and feeding so they grow through the damage, and clean up weedy brassica relatives nearby.
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 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 establishment. 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.The larvae of the cabbage root fly tunnel into brassica roots; the adult lays eggs at the stem base, and the maggots feed below, sometimes killing young plants. 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.
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 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 brussels sprouts 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 5 to 7 years where clubroot is known), keep soil pH up, improve drainage, and avoid moving infested soil on tools and boots.
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 the leaves and sprouts.Yellow, V-shaped lesions spread inward from the leaf margins, with the veins inside the V turning black; the disease moves through the vascular system and can blacken and rot foliage and sprouts. 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 good 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 with rings inside them, like a tiny target. Bad cases yellow the leaves and can spot the sprouts.Dark lesions enlarge into circular spots with characteristic concentric rings (a target-spot look) and a yellow halo; severe spotting downgrades the leaves and can blemish the sprouts. Favored by warm, wet conditions. Cause A fungus that spreads in warm, wet weather and infects the leaves, leaving target-like spots. It is worse on crowded, damp plantings and can come in on infected seed.Fungi in the genus Alternaria (chiefly A. brassicicola) infect brassica foliage, spreading by spores in wind and splashing water; infected seed, crop debris, and long leaf wetness drive it. Organic treatment Remove and destroy badly spotted leaves, improve airflow so leaves dry quickly, and use a copper spray if it spreads. Avoid wetting the leaves when you water.Remove and destroy spotted leaves and debris, improve airflow, avoid overhead watering, and apply a copper-based fungicide if pressure is high. Prevention Start with clean seed, rotate away from brassicas, space plants for airflow, water at the soil line, and clear away old plant debris.Use clean, disease-free seed (a hot-water treatment helps), rotate about 3 years away from brassicas, space for airflow, water at the soil line, and clear crop debris that harbors spores.
Symptoms Pale yellow blotches on top of the leaves, with fuzzy grayish growth on the underside, mostly in cool, damp weather. Bad cases discolor the leaves and can spot the sprouts.Pale yellow patches form on the upper leaf surface with a fuzzy gray growth underneath, mainly in cool, damp weather; severe infection discolors leaves and can blemish the sprouts. Brussels sprouts' cool, humid season overlaps the weather it likes. Cause A mold-like disease that loves cool, wet, humid weather and spreads through the air and water. Wet leaves and crowded plants 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. Organic treatment Open up the airflow so leaves can dry, remove the worst leaves, and use a copper spray if it's spreading. It's hard to stop once the weather stays damp.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 instead of from above, 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.
