Pests
Symptoms Leaves get yellow spots, then brown and wilt, and you find clusters of shield-shaped gray-brown bugs and their bronze eggs on the undersides of leaves near the base of the plant.Leaves develop yellow specks that brown and wilt, and heavily fed vines wilt rapidly and turn brittle, a damage pattern sometimes called anasa wilt. Flat bronze egg clusters appear on leaf undersides along the veins, and gray-brown adults and pale nymphs cluster near the crown and under debris. Cause Squash bugs pierce the leaves and stems and suck out the juices, which makes the vines wilt. They breed through the summer and hide in plant debris over winter.The squash bug, a true bug that feeds with piercing-sucking mouthparts on cucurbit foliage and stems, injecting saliva that wilts and browns the vines. Populations build through the season and are hardest to control once nymphs are large; the bugs overwinter as adults in garden debris. Organic treatment Pick the bugs off by hand and scrape off the egg clusters under the leaves. A board laid on the ground overnight draws them underneath, then lift it in the morning and destroy them. Treat the young bugs with insecticidal soap.Hand-pick adults, crush the egg masses on leaf undersides, and trap bugs by laying a board near the plants overnight, then lifting it in the morning and destroying the cluster underneath. Target young nymphs with insecticidal soap, since large nymphs and adults are tough to kill. Prevention Cover young plants until they flower, check under the leaves for eggs early in the season, and clean up old vines after harvest so the bugs have nowhere to overwinter.Use row cover on young plants until flowering, clean up vines and debris at season's end to cut overwintering sites, and rotate cucurbits. Scout leaf undersides for the bronze egg clusters from early in the season and act before nymphs mature.
Symptoms Small yellow beetles with stripes or spots chew on the leaves and flowers, especially of young plants. Worse, they can spread a disease called bacterial wilt that makes the vines collapse later.Small yellow beetles, striped or spotted, chew young leaves, stems, and flowers, and can scar developing fruit. The bigger threat is indirect: striped and spotted cucumber beetles transmit bacterial wilt, so beetle feeding on seedlings can be followed weeks later by sudden vine wilt. Cause Cucumber beetles feed on butternut plants and carry the germ that causes bacterial wilt, infecting the plant as they chew. Young seedlings are most at risk.Striped and spotted cucumber beetles feed on cucurbits and carry the bacterium that causes bacterial wilt in their gut, infecting plants as they feed. Seedlings are most vulnerable; once plants have several leaves they tolerate some feeding, and bacterial wilt is generally less severe in winter squash like butternut than in cucumber and melon. Organic treatment Cover young plants with row cover (remove it when flowers open), pick the beetles off, and use yellow sticky traps. Keeping the beetles down is the best way to avoid the wilt disease they spread.Protect seedlings with row cover removed at flowering, hand-pick beetles, and use yellow sticky traps to monitor and reduce numbers. Where bacterial wilt is a known problem, controlling the beetles is the most effective control of the disease, since there is no cure once a plant is infected. Prevention Cover seedlings until they flower, keep them growing strong, clear away weeds and old plants, and do not plant where squash-family crops grew last year.Exclude beetles from seedlings with row cover, keep young plants vigorous so they grow past the vulnerable stage, clear weeds and debris, and rotate away from where cucurbits grew. Aim control at the early-season colonizers that vector wilt.
Symptoms On many squash, a healthy plant wilts all at once in summer with sawdust-like specks at a hole near the base of the stem, and a fat white grub inside. Butternut rarely gets this, since the borer mostly avoids it, but it is still worth a look.On susceptible squash, a vigorous vine wilts suddenly in mid to late summer with sawdust-like frass oozing from a hole low on the stem and a fat white caterpillar tunneling inside. Butternut is the happy exception: as a Cucurbita moschata, it is far less susceptible than summer squash, zucchini, acorn, or Hubbard, so this collapse is uncommon, though heavy local pressure can still produce occasional damage. Cause A moth lays eggs at the base of the stem in early summer, and the grubs tunnel inside and kill the vine. The moth prefers thin-stemmed squash like zucchini and mostly leaves tough-stemmed butternut alone.The larva of the squash vine borer moth, which lays eggs at the stem base in early summer; the hatching larvae bore into the stem and cut off the plant's water. The moth strongly prefers thin-stemmed Cucurbita pepo squash and largely avoids the solid, tougher stems of moschata types like butternut, which is why butternut planted near a borer-ravaged zucchini often sails through untouched. Organic treatment Butternut seldom needs treatment. If you do find a borer, slit the stem with a knife, dig out the grub, and cover the spot with damp soil so it can re-root. Pull and destroy badly damaged vines.Rarely needed on butternut. If a borer does enter, slit the stem lengthwise, remove the larva, and bury that node under moist soil to re-root. Bury vines at the joints as they run so a damaged plant can survive on secondary roots, and remove infested vines to reduce next year's brood. Prevention Growing butternut is half the battle, since the borer mostly avoids it. If borers are bad where you live, cover young plants with a light row cover until they flower, then take it off so bees can reach the flowers.Choosing butternut is itself the main prevention, since moschata squash are a recognized borer-tolerant choice. Where pressure is severe, row cover from planting until flowering excludes the egg-laying moths, and scouting the stem base for frass from early summer catches the rare entry early.
Symptoms Tiny soft insects gather on the undersides of leaves and on new growth, making leaves curl and turn yellow, often with a sticky film. They can also spread viruses.Colonies of small soft-bodied insects, often melon aphids, cluster on leaf undersides and growing tips, causing leaves to curl, pucker, and yellow, with sticky honeydew and sooty mold following. Beyond direct feeding, aphids transmit mosaic viruses that mottle and distort the foliage. Cause Aphids are small insects that suck the plant's juices and multiply fast, especially on soft, over-fed growth. The sticky honeydew they leave behind grows black mold.Melon and other aphids suck sap and reproduce rapidly in warm weather, building up quickly on stressed or over-fertilized plants. The honeydew they excrete fosters sooty mold, and several aphid species spread cucurbit mosaic viruses. Organic treatment Blast them off with a strong spray of water and treat the undersides of the leaves with insecticidal soap, repeating every few days. Ladybugs and other helpful insects eat aphids, so welcome them.Knock colonies off with a strong jet of water and spray insecticidal soap or horticultural oil with thorough coverage of leaf undersides, repeating every few days. Conserve ladybugs, lacewings, and parasitic wasps, which usually bring aphids under control. Prevention Do not over-fertilize with nitrogen, check the undersides of leaves regularly, and let helpful insects do their work instead of spraying everything.Avoid excess nitrogen, which drives the soft growth aphids favor, scout leaf undersides and growing tips, and support natural enemies rather than spraying broadly. Reflective mulch deters aphids from young plants.
Diseases
Symptoms A white, powdery coating spreads over the leaves until they turn yellow and brown and die. The plant fades early, and the squash may not size up or sweeten well.White, powdery patches appear first on the upper and lower leaf surfaces and stems, spreading until leaves yellow, brown, and die back ahead of schedule. Early defoliation cuts the season short, reduces fruit size and the sugars that make butternut sweet, and exposes fruit to sunscald. Cause A fungus that spreads on warm, humid days, especially where plants are crowded and air does not move well. It does not need wet leaves to take hold.Powdery mildew fungi that thrive in warm conditions with high humidity but do not need leaf wetness, spreading by wind-blown spores. Crowded plantings, poor airflow, and shade worsen it, and it is one of the most common late-season winter-squash diseases. Organic treatment Treat early, at the first white spots, with a labeled fungicide like sulfur or horticultural oil, and remove badly affected leaves. Water the soil, not the leaves. Once it covers the plant it is hard to stop.Treat at the first spots, before it spreads, with a labeled fungicide such as sulfur or a horticultural oil or biofungicide, covering both leaf surfaces, and remove the worst leaves. Avoid overhead watering. Once it is widespread, control is mostly damage limitation. Prevention Pick resistant varieties, give plants plenty of room so air moves between them, plant in full sun, and water at the base. Start checking in midsummer and act at the first white spots.Choose resistant varieties (several butternut hybrids carry powdery-mildew resistance), space plants generously for airflow, plant in full sun, and avoid excess nitrogen and overhead watering. Scout from midsummer and treat at the first sign, since prevention and early action beat rescue.
Symptoms Yellow patches show on top of the leaves with fuzzy gray growth underneath, mostly in damp, humid weather. The spots brown and spread until the leaves die.Angular yellow blotches, bounded by the leaf veins, appear on the upper leaf surface, with a grayish or purplish fuzzy growth on the underside in humid weather. Spots brown and coalesce, and severe infection rapidly defoliates the vines. Cause A mold-like disease that spreads in wet, humid weather and needs wet leaves to infect. It can move through a planting quickly.A fungus-like water mold that spreads on wind-borne spores and needs leaf wetness and humidity to infect, so it flares in wet, humid spells and dewy conditions. It moves fast once established and is favored by crowding and prolonged leaf wetness. Organic treatment Open up the planting so leaves dry faster, remove the worst leaves, and use a labeled fungicide when wet weather sets in. Do not water over the leaves.Improve airflow, let foliage dry, remove badly affected leaves, and apply a labeled fungicide, covering leaf undersides, when conditions favor the disease. Avoid overhead irrigation, which keeps leaves wet and feeds the infection. Prevention Give plants room so air moves between them, water at the base, and watch closely in humid weather. Choose resistant varieties if downy mildew is common where you live.Space for airflow, water at the soil line rather than overhead, choose resistant varieties where available, and avoid working among wet vines. Scout closely in humid weather, when the disease can appear and spread quickly.
Symptoms Vines wilt and die even though the soil is wet. If you cut a wilted stem and pull the two ends apart slowly, infected sap stretches into sticky white strings.Individual leaves, then whole vines, wilt and collapse even though the soil is moist, often spreading until the plant dies. A field test helps confirm it: cut a wilted stem and slowly draw the cut ends apart, and infected sap pulls into thin, sticky white strands. Cause A germ spread by cucumber beetles as they feed. It blocks the plant's water pipes, so the vine wilts even when watered. Butternut is somewhat less prone than cucumbers or melons.A bacterium spread by striped and spotted cucumber beetles, which carry it in their gut and infect plants as they feed. It clogs the water-conducting tissue, so the plant wilts despite adequate water. Winter squash like butternut are generally less susceptible than cucumber and melon, but losses still occur. Organic treatment There is no cure once a plant has it, so pull and destroy infected plants. The real fix is keeping cucumber beetles down, since they spread it.There is no cure once a plant is infected; remove and destroy wilting plants to limit spread. Control is really beetle control, so management aims at keeping cucumber beetle numbers down, especially early in the season. Prevention Keep cucumber beetles under control, since they spread the disease. Cover young plants until they flower, and pull any plant that wilts and tests positive.Manage cucumber beetles from seedling stage with row cover removed at flowering, keep young plants vigorous, and remove infected plants promptly. Controlling the beetle vector is the most effective control of the disease.
