Pests
Symptoms Leaves that look skeletonized or lacy, with the tissue chewed away from underneath but the veins left behind. Both the spiny yellow young (larvae) and the round, coppery adult beetles feed on the undersides of the leaves, and when there are a lot of them they also chew stems and pods. The adult is yellow to copper colored with rows of small black spots on its back.Leaves taking on a skeletonized, lacy look as tissue is chewed away from the undersides, leaving the network of veins behind. Both the spiny yellow larvae and the dome-shaped, coppery adults feed on the leaf undersides, and when abundant they move on to stems and pods. The adult is yellow to coppery-brown with eight small black spots on each wing cover. Cause The Mexican bean beetle, a leaf-eating cousin of the ladybug. The adults come out of hiding near woods in spring, feed, then lay clusters of yellow eggs under the leaves, and several generations build up over the summer. It is worst in the Mid-Atlantic and southern Appalachian areas and is rarely a problem on the West Coast.The Mexican bean beetle (Epilachna varivestis), a leaf-eating member of the ladybeetle family. Adults emerge from overwintering near woodland edges, feed for a week or two, then lay clusters of yellow eggs on leaf undersides; there are about three generations a year, so populations build through the season. It is most damaging in the Mid-Atlantic and southern Appalachian regions and is largely absent from the Pacific Coast states. Organic treatment Pick off and destroy the adults, the yellow egg clusters, and the spiny young, looking under the leaves. Done early, this works well in a home garden. Beans can lose a fair amount of leaf without losing beans, so you do not need to spray for light damage. If they get bad, an organic spray such as spinosad is labeled for bean beetles, and a tiny helper wasp is sold to control them.Handpick and destroy adults, the yellow egg clusters, and the spiny larvae, checking leaf undersides; this is effective in a home patch caught early. Beans tolerate real defoliation without yield loss (about 30 percent before bloom, 15 percent during bloom and pod fill), so light feeding needs no spray. Where pressure is heavy, an organic option such as spinosad or a pyrethrin is labeled for bean beetles; the parasitic wasp Pediobius foveolatus is sold for biological control. Prevention Because most damage happens in July and August, fast-maturing beans planted very early or in late summer can mostly dodge it. The varieties Wade and Black Valentine hold up better. Clear and turn under the old plants right after harvest so the beetles have nowhere to overwinter, and move your beans to a new spot each year.Since most damage falls in July and August, quick-maturing varieties sown very early or in late summer can largely escape it. The varieties Wade and Black Valentine are tolerant. Work crop debris into the soil promptly after harvest to remove overwintering shelter, and rotate beans away from last year's bed.
Symptoms Clusters of tiny soft-bodied insects, usually green but sometimes black or pink, packed onto the growing tips and the undersides of leaves. Heavy feeding stunts young plants and slows them down, and a sticky residue may appear. Aphids can also spread virus diseases from plant to plant.Colonies of soft-bodied, pinhead-sized insects clustered on growing tips and leaf undersides, usually green but sometimes black, yellow, or pink. Heavy feeding stunts young plants and delays maturity as the insects withdraw large volumes of sap; a sticky honeydew and sooty mold may follow. Aphids also transmit the mosaic viruses of beans. Cause Several kinds of aphids, most common in cool, dry weather on small plants. They multiply fast and build up thick colonies before their natural enemies catch up. Warmer weather and helpful bugs like ladybugs usually knock them back.Several aphid species (Aphis and Macrosiphum), most prevalent in cool, dry weather on small plants. They reproduce rapidly, building dense colonies before natural enemies catch up; warm weather and predators such as ladybugs usually bring them down. Organic treatment Blast the colonies off with a strong spray of water, or use insecticidal soap, which works on contact. Start as soon as you see them. Once it warms up, ladybugs and other helpful insects usually take care of the rest.Knock colonies off with a strong spray of water, or treat with insecticidal soap, which gives good control on contact. Begin as soon as colonies are found. Once the weather warms, ladybugs and other natural enemies generally take over. Prevention Lay down reflective mulch, which confuses aphids and cuts both their feeding and the viruses they spread, and pull nearby weeds that shelter them. Do not overfeed with fertilizer, since the soft new growth is exactly what aphids like.Lay reflective mulch, which disorients aphids and reduces both feeding and virus spread, and control nearby weeds that harbor them. Avoid overfeeding with nitrogen, which produces the soft, lush growth aphids favor.
Symptoms Fine whitish or yellow speckling on the leaves at first, turning to a dried, bronzed look as they multiply. The clue is fine webbing on the undersides of the leaves. The mites themselves are tiny specks, easiest to see by tapping a leaf over white paper. They explode in hot, dry weather.A fine whitish or yellow stippling on the leaves at first, progressing to a bronzed, dried-out look as populations build; fine silken webbing over the leaf undersides is the giveaway. The mites are minute specks on the undersides, easiest to confirm by tapping a leaf over white paper. They build explosively in hot, dry weather, completing a generation in as few as eight days. Cause Two-spotted spider mites, tiny eight-legged relatives of spiders that pierce the leaf and suck out the contents. Hot, dry weather lets them build up fast, and dusty, dried-out plants are the most likely to be hit.Two-spotted spider mites (Tetranychus urticae), tiny eight-legged relatives of spiders that pierce leaf cells and suck the contents. Hot, dry conditions favor rapid buildup, and dusty, drought-stressed plants are most prone. Organic treatment Spray the undersides of the leaves with a strong jet of water to knock off the mites and webbing, and use insecticidal soap before they get too thick. Keeping the plants well watered and unstressed slows them down, and helpful bugs pitch in.Hose the undersides of leaves with a strong spray of water to dislodge mites and webbing, and treat with insecticidal soap before numbers climb too high. Keeping plants well watered and unstressed slows buildup, and ladybugs and other predators help. Prevention Keep the soil evenly moist, because dried-out plants are much more likely to get mites, and keep dust down. Check the undersides of the leaves during hot, dry weather so you catch them early.Maintain even soil moisture, since drought-stressed plants are far more mite-prone, and avoid the dusty conditions mites thrive in. Watch the undersides of leaves closely through hot, dry spells so you catch the buildup early.
Symptoms Large ragged holes chewed in the leaves, and on young plants, chewing around the stem near the soil that can kill seedlings. The adult is a small beetle, usually reddish or yellowish, with a few black spots running down each wing cover. The color varies a lot. Early-season damage is the worst because it thins out the plants.Large, irregular holes chewed in leaves, and on young plants, girdling of stems near the soil line that can thin the stand. The adult is small and variable in color, usually reddish or yellowish, marked with a handful of black spots set along each wing cover near where the two covers meet. Damage early in the season matters most because it reduces the stand. Cause The bean leaf beetle, which is rarely a serious problem in most home gardens. The adults chew leaves and stems, and young seedlings are the most at risk.The bean leaf beetle (Cerotoma trifurcata), rarely a serious pest in most home gardens. Adults feed on foliage and stems, with seedlings the most vulnerable stage. Organic treatment Picking them off and the same steps you would use for Mexican bean beetle usually keep them in check. Beans can lose a good bit of leaf without losing beans, so light damage needs nothing. Focus on protecting young seedlings, which are the most at risk.Handpicking and the same measures used against Mexican bean beetle generally keep it in check; beans tolerate considerable leaf loss without yield penalty, so light feeding needs no action. Protect emerging seedlings, the vulnerable stage, where beetles are active. Prevention Clear away the old plants after harvest and move your beans each year so the beetles have nowhere to overwinter. A lightweight row cover over young seedlings protects them through the risky early weeks if this beetle is a problem where you are.Clear crop debris after harvest and rotate beans to deny overwintering sites. A floating row cover over emerging seedlings protects the stand through the vulnerable early weeks where the beetle is a known problem.
Diseases
Symptoms Rust-colored bumps, mostly on the undersides of the leaves. Badly infected leaves turn yellow, wilt, and fall off. Stems and pods can get it too. It shows up in humid weather and can hit most kinds of beans.Rust-colored, raised spots that form mainly underneath the leaves; badly infected leaves yellow, wilt, and drop. Stems and pods can be infected too. It develops under humid conditions and can affect most types of beans. Cause A fungus that survives the winter in the soil, on old plant debris, and even on stakes used the year before. Humid weather is what lets it take hold and spread.The fungus Uromyces appendiculatus. It carries over from one season to the next in the soil and on leftover plant debris, and can persist on stakes or poles reused from a previous crop. Humid conditions drive infection and spread. Organic treatment Pick off and throw away (do not compost) infected leaves and give the plants room to breathe. Where rust is bad, a sulfur dust or spray gives good control if you start as the plants begin to flower and repeat every week or two, following the label.Remove and destroy infected leaves and improve airflow. Where rust has been severe, a sulfur dust or spray gives good control when begun as the plants start to bloom and repeated on a 10-to-14-day schedule; follow the label. Prevention Move your beans to a new spot if rust has been a problem, since the fungus carries over on old plants and stakes, and clean or replace stakes between years. Water at the base instead of overhead, give plants room, and pick a rust-resistant variety if it keeps coming back.Rotate beans where rust has been a problem, since the fungus carries over on debris and stakes; clean or replace stakes between seasons. Avoid overhead watering and space plants for airflow, and choose rust-resistant varieties where it recurs.
Symptoms Black, sunken spots about half an inch across on the pods, the clearest sign, sometimes with a pinkish ooze in wet weather. The veins on the undersides of leaves turn black, and spots show up on stems too. It shows up in cool, wet spring and fall weather, not in hot, dry summers.Black, sunken lesions about half an inch across on pods, the most prominent sign, sometimes oozing salmon-colored spores in wet weather; the veins on lower leaf surfaces turn black, and lesions appear on stems and seedling leaves. It develops in cool, wet spring and fall weather, not in hot, dry summers. Cause A fungus that rides in on infected seed and survives up to two years on old plant debris in the soil. Splashing water spreads it, and cool, wet weather is when it strikes.The fungus Colletotrichum lindemuthianum, carried on infected seed and surviving up to two years on plant debris in the soil. Splashing water spreads it, and cool, wet conditions favor infection. Organic treatment You cannot cure tissue that is already infected; pull and throw away (do not compost) affected plants and debris to slow it down. On snap beans, a copper fungicide can help if you start early, but keeping seed clean and rotating does most of the work.There is no cure for infected tissue; remove and destroy affected plants and debris to limit spread. On snap beans, a copper fungicide or chlorothalonil can suppress it when started early; cultural control is the mainstay for a home crop. Prevention Plant certified disease-free seed and do not save seed from an infected crop. Clear away all the old plants after harvest, and do not grow beans in that spot for two to three years. Water at the base and avoid splashing soil up onto the plants.Plant certified disease-free seed and do not save seed from an infected crop. Remove all plant debris after harvest, and do not plant beans where the disease occurred for two to three years. Avoid overhead watering and splashing soil onto the plants.
Symptoms Two related diseases. Halo blight makes pale greenish-yellow rings around brown spots on the leaves and shows up in cool weather. Common blight turns leaves brown so they drop fast, with no ring, and likes warm weather. Both hit stems, leaves, and pods, and both spread in rain and damp conditions.Two related diseases. Halo blight shows light greenish-yellow halos around brown leaf spots and appears in cool weather; common blight turns leaves brown so they drop quickly, with no halo, and favors warm weather. Both infect stems, leaves, and pods, and both are spread by rain and damp conditions. Cause Two kinds of bacteria, one causing common blight and one causing halo blight. Both start on infected seed, spread easily when it is wet, and survive up to two years on old plant debris in the soil.Two bacteria, Xanthomonas campestris pv. phaseoli (common blight) and Pseudomonas syringae pv. phaseolicola (halo blight). Both start on infected seed, spread readily in moisture, and survive up to two years on plant debris in the soil. Organic treatment There is no cure once plants are infected; copper sprays every 10 days can slow it down. Water at the base, not overhead, and do not touch the plants when the leaves are wet, since that carries the bacteria from plant to plant.There is no cure once plants are infected; copper fungicides applied on a 10-day schedule can slow spread. Avoid overhead watering and do not handle plants when foliage is wet, which moves the bacteria from plant to plant. Prevention Buy new, certified seed each year instead of saving your own, since the disease travels on seed. Do not grow beans in the same spot more than once every three years, and keep out of the patch when the leaves are wet.Buy new, certified seed each year rather than saving it, since the disease is seedborne. Do not plant beans in the same spot more often than every third year, and stay out of the planting when the foliage is wet.
Symptoms Seeds that rot before they come up, or young seedlings that come up stunted, with a soft, watery rot at the soil line. The roots die and the leaves turn yellow. It is worst in cool, wet soil that makes the seeds sit too long before sprouting.Seeds that rot before emerging, or young seedlings that come up stunted, with a watery soft rot just above or below the soil line; roots die and leaves yellow. The damage shows up most in cool, wet soils that slow germination and keep seedlings vulnerable. Cause Several fungi that live in the soil and infect seeds and young seedlings. The usual culprits are Rhizoctonia, Pythium, and Fusarium. Cool, wet, poorly drained soil and damage to the roots at planting are what let them in.Several soilborne fungi that infect seeds and young seedlings. The ones usually responsible are Rhizoctonia, Pythium, and Fusarium species. Cool, wet, poorly drained soil and root injury at planting set the stage for them. Organic treatment There is no saving seedlings that have rotted; replant once the soil is warmer and drains better. Pulling affected plants and improving drainage limits the loss. The main thing is prevention, since these fungi are already in the soil.There is no rescue for rotted seedlings; replant into warmer, better-drained conditions. Removing affected plants and improving drainage limits further loss. The real lever is prevention, since the fungi are already in the soil. Prevention Wait until the soil has warmed to about 69°F before planting, and use raised beds in well-drained ground instead of low, wet spots. Avoid damaging the roots when planting, move your beans around the garden each year, and clear away old plants after harvest.Wait until the soil has warmed to about 69°F at a 4-inch depth before sowing, and plant on raised beds in well-drained ground rather than low, wet spots. Avoid root injury at planting, rotate beans with other vegetables, and clear crop debris after harvest.
Symptoms Small, soft, watery spots on stems, leaves, and pods that grow fast in cool, damp weather, join together, and choke off the stem. Affected pods collapse into a brown, watery mush, soon covered in white cottony mold. Crowded, overfed plants with poor airflow are the most at risk.Small, soft, watery spots on stems, leaves, and pods that enlarge fast under cool, moist conditions, run together, and choke off the stem. Affected pods collapse into a brown, watery mush, soon covered by a white cottony fungal growth. Dense, overfed plantings with poor airflow are most at risk. Cause A fungus that thrives in cool, damp weather and heavy, crowded growth. Too much fertilizer makes the lush, dense plants that trap the still, humid air the mold needs.The fungus Sclerotinia sclerotiorum, favored by cool, moist conditions and heavy, dense plant growth. Too much fertilizer drives the lush vine growth that creates the still, humid canopy the disease needs. Organic treatment There is no home-garden spray for this one; you manage it by how you grow. Pull and throw away (do not compost) infected plants, and open up the spacing between plants and rows so the leaves dry out faster.There is no recommended chemical control for the home garden; management is cultural. Remove and destroy infected plants, and improve air circulation between plants and rows to dry the canopy. Prevention Give plants and rows room for air to move instead of crowding them, and go easy on fertilizer, since too much makes the heavy growth the mold likes. Water at the base and avoid keeping the plants wet and packed together.Space plants and rows for good airflow rather than crowding, and go easy on fertilizer, since excess nitrogen feeds the heavy vine growth that favors the disease. Avoid overhead watering and the wet, still conditions the fungus needs.
