Chayote squash

Flea beetles are small (1/16-inch) shiny beetles that jump like fleas when disturbed. They chew small round 'shothole' or 'pinhole' damage in leaves and can destroy emerging cotyledons of broccoli or eggplant in 24 hours. Most species are host-family specific — crucifer flea beetle on brassicas, tuber flea beetle on potatoes, eggplant flea beetle on solanaceous crops.

Triggers: Overwinter as adults in leaf litter and field margins. Active at mid- to late-spring temperatures. Warm winter → higher next-spring populations (NC State). Hot dry conditions amplify damage on stressed seedlings.

Risk fades when: UMN: 1-2 generations in Minnesota, populations crash after mid-June

Japanese beetle adults feed gregariously on the foliage and flowers of more than 300 host species, skeletonizing leaves by chewing tissue between the veins. Larvae (white C-shaped grubs) damage turf and root systems. Adults are active during the warmest part of sunny summer days, when populations can rapidly defoliate roses, grapes, and ornamentals. Do not use Japanese beetle traps near plants — the lures attract more beetles than they catch.

Triggers: One generation per year. Overwinters as larva in soil. Adults emerge late June-early July (peak July). Adults active during warmest part of sunny days. Females lay 40-60 eggs in turf 3 inches deep.

Risk fades when: Multiple sources confirm one generation, peak July

Cool, rainy, or very hot weather reduces bee activity and flower fertility.

On Chayote: Cool, rainy, or very hot weather reduces bee activity and flower fertility.

Prevention: Hand-pollinate early flowers if needed and plant pollinator-friendly flowers nearby.

The white powdery coating you see on cucumber, squash, and melon leaves. It rarely kills plants outright but weakens them and reduces yield. Unlike most plant diseases, it actually thrives in warm DRY weather — rain washes spores off and slows it down.

Triggers: Does NOT need rain. Thrives in warm, dry weather with moderate humidity (50-90% RH). Heavy rain can suppress it by physically washing spores off the foliage.

On Chayote: Dense foliage and late-season humidity encourage mildew on leaves.

Prevention: Space well, avoid overhead watering when possible, and remove badly infected leaves.

Risk fades when: Development stops above 100°F. Extended rain also suppresses spread by knocking spores off the leaves.

Microscopic soil-dwelling roundworms that burrow into plant roots and cause swollen knots (galls). Above ground, the plant looks stunted, yellowed, and wilted even with plenty of water. They attack over 2,000 plant species, so almost nothing is safe. They're most active in warm soil (70-85°F) and do more damage in sandy soils, where they move easily. Once a bed has them, populations stick around for years.

Triggers: Soil temperatures of 70-85°F are ideal for them; below 60°F they go dormant. Sandy soils make it easy for them to move and reproduce, while heavy clay slows them down considerably. In warm soil, a full generation completes in about 27 days.

Risk fades when: Activity drops sharply once soil cools below 60°F. Damage stops accumulating for the season, but the population stays in the soil and returns when warmth does.

Root-knot nematodes are microscopic plant-parasitic roundworms that infect roots and cause characteristic galls (knots), distinguishable from beneficial legume nitrogen-fixing nodules because the galls cannot be rubbed off. Infected plants show stunting, yellowing, and wilting in heat. They are most damaging in sandy soils, in warm weather, and after years of growing susceptible crops in the same beds. NC State estimates two-thirds of NC crop fields are affected.

Triggers: Sandy/light-textured soils most favorable. Soil temps 70-85°F most active. Inactive below 60°F (NC State). Continuous cropping of susceptible hosts builds populations. Moderate drought amplifies damage. Egg-to-adult 27 days at typical growing temps.

Risk fades when: NC State

A celery and celeriac-specific Septoria disease (not the same as the tomato version). It causes small leaf and petiole spots with tiny black fruiting bodies (pycnidia) inside each spot. Spreads from infected seed and transplants, and gets worse anywhere sprinkler irrigation or rain keeps celery leaves wet.

Triggers: Long stretches of leaf wetness, rain or sprinkler irrigation, infected seed or transplants, and humid celery canopies all drive risk.

Risk fades when: Reducing leaf wetness and switching from overhead to drip irrigation cuts new Septoria infection periods.

Slugs and snails are nocturnal mollusks that chew irregular holes in leaves and clip off succulent seedlings. They leave characteristic silvery slime trails. Hermaphroditic and prolific, brown garden snails lay around 80 eggs per month for up to six clutches per year.

Triggers: Active at night and early morning in damp conditions. Coastal CA and southeast — active year-round. Spring rains and dense ground cover (mulch, debris, weeds) create harborage.

Risk fades when: UC IPM

Spider mites are tiny arachnids (1/50 inch) that feed on the undersides of leaves, producing characteristic silver-yellow stippling. Heavy populations produce visible webbing that interferes with pesticide coverage. They thrive in hot dry weather and drought-stressed plants. The two-spotted spider mite feeds on more than 180 cultivated plant species.

Triggers: Hot dry conditions; >90°F lifecycle <2 weeks. Drought stress amplifies. Broad-spectrum sprays (carbaryl, pyrethroids) trigger outbreaks by killing predators. Wisconsin Ext: 'as little as a month without significant rain during the growing season can favor a mite outbreak.'

Risk fades when: UMN Extension

Thrips are tiny (1/16 inch) slender insects with fringed wings that puncture and rasp leaf surfaces, leaving silver stippling with black frass dots. The biggest concern is virus vectoring: western flower thrips is the principal vector of tomato spotted wilt virus (TSWV) and impatiens necrotic spot virus (INSV), which affect more than 600 plant species. Greenhouse and high tunnel infestations can be devastating.

Triggers: Hot dry weather; greenhouse/high tunnel environments. Female lays eggs inside leaf tissue. 2 larval stages feed; 2 non-feeding pupal stages in soil/litter. Lifecycle 10-21 days. Many overlapping generations. Bridge crops (spring wheat, peach, strawberry per NC State) build populations before vegetable hosts available.

Risk fades when: Wisconsin Hort, NC State

Leafminers are tiny fly larvae that feed between the upper and lower surfaces of leaves, creating winding pale tunnels or blotchy patches. They rarely kill plants but can ruin the marketability of leafy greens grown for foliage. Allium leafminer is an emerging pest in the eastern US (first detected in Pennsylvania in 2017) that damages onions, garlic, leeks, and chives.

Triggers: Liriomyza trifolii: 1 generation in ~1 month at typical greenhouse temps, 14 days at 95°F, 64 days at 59°F (UC IPM). Adults active mid-day. Allium leafminer emerges late March-early April, second flight September-October. Broad-spectrum insecticides trigger outbreaks by killing parasitoids.

Risk fades when: UMD

The parsleyworm is the larva of the eastern black swallowtail butterfly, a beneficial pollinator. Caterpillars feed on Apiaceae crops — parsley, dill, fennel, carrot, celery, parsnip — and can rapidly defoliate small plantings in their last instar. Most gardeners tolerate or relocate the caterpillars rather than control them, as they become important pollinators.

Triggers: Overwinters as chrysalis on tree bark or structures. Adults emerge May-June. 2-3 generations/year in NC. Eggs single on Apiaceae leaves; 10 days from hatch to pupation.

Risk fades when: NC State: 2-3 generations/year