Pests
Symptoms Lots of tiny round holes peppering the leaves, like someone fired birdshot at them. The beetles are very small, shiny, and dark, with big back legs, and they jump away like fleas the moment you get close. They are worst on young radish seedlings in spring. The holes look alarming but a fast-growing radish usually shrugs them off; the real worry is a small seedling losing too many leaves, which slows it down and makes the root tougher and hotter.Tiny, round, shot-hole punctures riddling the leaves, the classic flea-beetle signature. The beetles themselves are minute (about 1/16 to 1/8 inch), shiny black, bronze, or bluish, with enlarged hind legs, and they spring away like fleas when disturbed. Damage is worst on young spring seedlings and along bed edges, and a heavily fed-on stand can be stunted or wilted. The leaf damage is mostly cosmetic on a fast garden radish that grows through it, but a seedling losing a large share of its leaf area slows down, which for radishes means a tougher, hotter root. Cause Small beetles that spend the winter in leaf litter and weeds and come out in early spring hungry for cabbage-family leaves. Radishes and their relatives (arugula, mustard) are among their favorite foods, so much so that gardeners sometimes plant radishes on purpose to lure flea beetles away from other crops. They do the most damage in spring and early summer and ease off as it gets hotter.Adult flea beetles (several species, including crucifer and striped flea beetles) that overwinter in leaf litter and field edges and emerge in early spring to feed on Brassica-family foliage. Radish, arugula, mustard, and other crucifers are highly preferred hosts, which is also why these crops are used as trap crops to pull beetles off other vegetables. They are most damaging in spring and early summer and taper off as the season warms. Organic treatment A healthy, well-watered radish patch usually grows right through light flea-beetle damage. If the little seedlings are getting hammered, cover the row with a floating row cover (a light fabric) right after planting and tuck in the edges so the beetles cannot get under it. Dusting with kaolin clay helps, and sprays like spinosad or pyrethrin are options if seedlings are losing a lot of leaf. Check in the cool morning, when the beetles are slow.On a fast garden radish, a vigorous, well-watered stand usually outgrows light feeding without intervention. Where pressure is heavy on seedlings, a floating row cover set at sowing and sealed at the edges excludes the beetles entirely. Kaolin clay can reduce feeding, and spinosad or pyrethrin products are labeled options if a seedling stand is losing more than roughly a quarter to a third of its leaf area; cool mornings are the easiest time to scout, since the beetles are sluggish. Prevention Clear away old plants and weeds at the end of the season so fewer beetles survive the winter nearby. Covering the seedbed with a row cover is the surest fix for early spring radishes. Planting a bit later, after the first wave of beetles, and keeping the radishes growing fast with steady water also help. You can even plant a little arugula or mustard nearby as bait to draw the beetles away.Clean up crop debris and weeds at the end of the season to cut overwintering sites. A row cover over the seedbed is the most reliable defense for early spring sowings. Planting a little later, once the first beetle flush has passed, and keeping the stand growing fast with even moisture both reduce the impact. A sacrificial trap crop of arugula or mustard can pull beetles off the main planting.
Symptoms The trouble is underground. Small white legless maggots tunnel into the radish, leaving winding brown trails that spoil the root and let rot set in. Aboveground the plant may look pale, wilted, or stunted. It shows up most in cool, wet springs and in soil full of un-rotted material. A tunneled radish is ruined, but pulling and tossing it right away gets the maggots out before they can turn into the next generation of flies.The damage is underground: small, white, legless maggots tunnel and score the surface and interior of the root, leaving winding brown trails that ruin the radish and open the door to rot. Aboveground, infested plants may look off-color, wilted, or stunted. It is most common in cool, wet springs and in soil rich in undecomposed organic matter. A scored radish is unsalable but a useful sentinel, since pulling and destroying it removes maggots before they pupate. Cause The maggots (young larvae) of the cabbage maggot fly, a small gray fly. It spends the winter as pupae in the soil, and in spring the females lay lots of tiny white eggs at the base of cabbage-family plants. The eggs hatch in about a week and the maggots burrow into the roots for three to four weeks. It goes after the whole cabbage family, radishes, turnips, cabbage, broccoli, and kale, and is worst in cool, damp spring weather.Larvae of the cabbage maggot (Delia radicum), a small gray fly that overwinters as pupae in the soil. In spring the adults emerge and females lay 50 to 200 white eggs at the base of crucifer stems and in nearby soil cracks; the eggs hatch within about a week and the maggots feed on roots for three to four weeks before pupating. It attacks the whole cabbage family, including radish, turnip, cabbage, broccoli, and kale, with several generations a year and the worst damage in cool, moist spring weather. Organic treatment You cannot save a radish that is already tunneled. Pull up and throw away (do not compost) the affected ones so the maggots cannot grow into more flies. There is no good home spray for this, and sprays do nothing once the maggots have already left the root, so prevention is the real fix.There is no rescue for a root already tunneled. Pull and destroy infested radishes (do not compost them) to keep maggots from completing their cycle; a damaged early sowing can act as a trap crop if removed promptly. Insecticide drenches are difficult and rarely worthwhile in a home garden, and are pointless once the maggots have left the root to pupate. Prevention The best home defense is a row cover (a light fabric) laid over the bed right after sowing and tucked in at the edges, so the flies cannot reach the plants to lay eggs, just make sure the soil is not already carrying them from an earlier crop. Move radishes away from spots that grew cabbage-family crops recently, avoid fresh manure and freshly dug-in plant material that attract the flies, and lean toward fall planting, which usually has fewer maggots than cool wet spring.A floating row cover sealed at the edges at sowing is the most effective home defense, since it blocks the egg-laying flies; be sure no flies are already in the soil from a previous crop. Rotate radishes and other crucifers away from beds that grew them recently, avoid fresh manure and freshly turned-under cover crops or residue that attract the flies, and time spring sowings to dodge the main egg-laying flush or favor fall plantings, which see less pressure.
Symptoms Narrow, clean holes drilled into the radish. If you dig around, you may find skinny, hard, yellowish-brown worms in the soil. It is most common in ground that was recently lawn or grass.Narrow, clean tunnels bored straight into the root, distinct from the surface scoring of cabbage maggot. The culprits are slender, hard-bodied, yellow-brown larvae found in the soil. Damage is most common in beds recently converted from sod or grass, where wireworm populations are high. Cause Wireworms are the larvae of click beetles. They live in the soil for years and chew on roots and seeds of many plants. They are most common in soil that used to be lawn or grassy ground.Wireworms, the soil-dwelling larvae of click beetles, which feed on roots, tubers, and germinating seed across many crops. They persist for years in soil and are most abundant in ground newly broken from grass or sod. Organic treatment There is no fast fix once they are in the soil. Harvest radishes on time so they sit in the ground less, and over a season or two, working the soil and not planting roots right after grass helps bring numbers down.There is no quick home cure once they are present. Harvest promptly so roots spend less time exposed, and reduce populations over time by cultivating the soil and avoiding planting root crops in freshly broken sod. Prevention Do not plant radishes in ground that was lawn or grass last year, since that is where wireworms gather. Turning over and working the soil, and moving root crops to a different spot, brings numbers down over time.Avoid sowing radishes and other root crops in beds just converted from lawn or pasture. Cultivating the soil exposes wireworms to predators and weather, and rotating away from heavily infested ground reduces damage over seasons.
Diseases
Symptoms Aboveground the plant looks stunted and yellow and wilts in the afternoon sun, then perks up at night. Underground is the giveaway: instead of a clean radish, the roots swell into lumpy, distorted clubs and galls that eventually rot. It lives in the soil and builds up when you grow cabbage-family crops in the same spot over and over, especially in wet, acidic soil.Aboveground, plants are stunted, yellowish, and wilt in the heat of the day even in moist soil, recovering overnight. The diagnostic sign is below ground: the roots are swollen, distorted, and clubbed into gnarled galls rather than forming a clean radish, and they later rot. It is a soilborne disease that builds up where crucifers are grown repeatedly, and it is favored by wet, acidic soil. Cause A soil organism (Plasmodiophora brassicae) that attacks the roots of cabbage-family plants and survives in the soil for years. Wet, poorly drained, acidic soil makes it worse, and it spreads on dirty tools and soil moved from an infected bed.Plasmodiophora brassicae, a soilborne pathogen that infects the roots of cabbage-family plants and persists in soil as resting spores for many years. Wet, poorly drained, acidic soils favor infection, and the disease spreads on contaminated soil, tools, and transplants. Organic treatment There is no way to cure a plant that has it, so pull and throw away (do not compost) the affected ones. The fix is for next time: improve drainage, raise the soil pH closer to neutral with lime, which holds the disease back, and keep cabbage-family crops out of that spot for a few years.There is no cure once a plant is infected; remove and destroy affected plants and do not compost them. Management is preventive across seasons: improve drainage and raise soil pH toward neutral, which suppresses the pathogen, and rotate crucifers out of the bed for several years. Prevention Do not grow radishes or other cabbage-family crops in the same bed year after year; move them around on a few-year cycle. Keep the soil well drained and add lime to bring the pH closer to neutral, and avoid carrying soil from an infected bed on your tools. A raised bed with clean soil avoids it where it is a known problem.Rotate radishes and other crucifers on a multi-year cycle, since the pathogen builds in soil grown to the family. Keep soil well drained and limed toward a neutral pH, start with clean soil and tools, and avoid moving soil from an infested bed. Raised beds with clean mix sidestep the problem where it is established.
Symptoms Yellow, V-shaped patches creeping in from the edges of the leaves, with the point of the V aimed at the center vein, and the veins in those patches turning dark. The leaves yellow and die, and a bad case can rot the plant. It is a bacterial disease that hits the whole cabbage family in warm, wet weather.Yellow, V-shaped lesions advancing inward from the leaf margins, with the V pointing toward the midrib and the veins in the affected area turning dark. Infected leaves yellow and die, and severe infection can rot the plant. It is a bacterial disease of the whole cabbage family, spread in warm, wet conditions. Cause A bacterium (Xanthomonas campestris) that can travel on seed and splashing water and gets into the leaves through their edges and any wounds. Warm, humid, wet weather brings it on, and it spreads on infected seed, water, tools, and old plant debris among cabbage-family plants.Xanthomonas campestris pv. campestris, a seedborne and splash-spread bacterium that enters through leaf margins and wounds. It is favored by warm, humid, wet conditions and spreads on contaminated seed, water, tools, and crop debris across cabbage-family crops. Organic treatment You cannot cure leaves that are already infected. Pull and throw away affected plants, stay out of the bed when the leaves are wet, and clean up old plant material. Radishes grow so fast they usually finish before it gets bad, so clean seed and good habits handle most of it.There is no cure for infected tissue. Remove and destroy affected plants, avoid working among plants when the foliage is wet, and clear crop debris. Because the fast radish crop usually finishes before severe disease develops, cultural control and clean seed do most of the work. Prevention Use clean, disease-free seed, do not grow cabbage-family crops in the same spot repeatedly, and clear away old plant debris. Water at the soil instead of overhead, do not handle wet plants, and give them room so the leaves dry fast.Start with clean, disease-free seed, rotate crucifers out of the bed, and clear debris that harbors the bacterium. Water at the base rather than overhead, avoid handling wet plants, and space for airflow so foliage dries quickly.
Symptoms Dark, round spots on the leaves, sometimes ringed or with a yellow edge, that grow and run together in wet weather. It mostly affects the leaves and is rarely a big deal on fast radishes you grow for the root, though a bad case can slow the plant down.Dark, roughly circular spots on the leaves, sometimes with concentric rings or a yellow halo, that enlarge and merge in wet weather. It is primarily a foliar disease and rarely a problem on a fast garden radish harvested for its root, but heavy infection can reduce vigor. Cause Alternaria fungi that travel on seed and survive on old plant debris, spreading in splashing water and needing wet leaves to take hold. Warm, humid weather with wet foliage brings it on.Alternaria fungi that are seedborne and survive on crop debris, spreading in splashing water and needing leaf wetness to infect. Warm, humid weather and prolonged wet foliage drive it. Organic treatment Pick off the worst leaves, water at the soil in the morning so leaves dry quickly, and clean up debris. Radishes usually grow faster than the disease can spread, so clean seed and good airflow are enough.Remove badly spotted leaves, water at the base in the morning so foliage dries, and clear debris. The fast crop usually outpaces serious damage; clean seed and airflow are the main levers. Prevention Use clean seed, water at the base instead of overhead, give plants room so the leaves dry, and clear away old plant material between plantings.Use clean seed, avoid overhead watering, space for airflow, and rotate crucifers and clear debris that carry the fungi between seasons.
Symptoms Seeds that never come up, or tiny seedlings that flop over and die soon after sprouting, with a dark, pinched, water-soaked spot on the stem right at the soil line. You see it as bare gaps in the row. Because radishes sprout and grow so fast, this is much less of a worry than with slow crops, but cold, soggy, poorly drained soil can still bring it on.Seeds that fail to emerge, or young seedlings that topple and collapse soon after emergence with a dark, water-soaked pinch at the stem base right at the soil line. Losses appear as bare gaps in the row. Because radishes germinate fast and grow quickly, damping-off is far less of a threat than in slow-germinating crops, but cold, wet, poorly drained seedbeds still invite it. Cause Soil organisms (mostly Pythium and Rhizoctonia) that attack sprouting seeds and baby seedlings. They thrive in cold, wet, poorly drained soil and when you overwater.Soilborne pathogens, chiefly Pythium and Rhizoctonia, that attack germinating seed and young seedlings. They are favored by cold, wet, poorly drained soil and overwatering. Organic treatment Seedlings that have collapsed will not recover. Ease off watering and let the soil surface dry out a bit, and re-sow the bare spots once it is warmer and drains better. Mostly this one is about prevention.Affected seedlings cannot be saved. Stop overwatering and let the surface dry somewhat, and re-sow gaps in warmer, better-drained conditions. Prevention is the real control. Prevention Wait to sow until the soil is warm enough and not cold and soggy, use fresh seed, do not plant too deep, and improve drainage or use a raised bed if your soil is heavy. Do not overwater while seeds are sprouting.Sow into warm-enough, well-drained soil rather than cold, wet ground, use fresh seed, avoid sowing too deep, and improve drainage or use raised beds on heavy soil. Do not overwater the seedbed.
