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Identify and control common garden insects and pests
Also see: Plant Disease Guide
Fungal, bacterial, viral infections and nutrient deficiencies
Over 4,000 aphid species exist. They feed by piercing plant tissue and sucking phloem sap. Colonies reproduce rapidly — a single female can produce 80+ offspring per week without mating. Ants often "farm" aphids for their honeydew and protect them from predators.
Spider mites (family Tetranychidae) are arachnids, not insects. Two-spotted spider mite (Tetranychus urticae) is most common. They pierce cells and extract contents. A generation completes in as few as 7 days in hot weather, enabling rapid resistance to pesticides.
Whiteflies (family Aleyrodidae) are not true flies but are closely related to aphids. The sweetpotato whitefly (Bemisia tabaci) and greenhouse whitefly (Trialeurodes vaporariorum) are most common. They spread several plant viruses including TSWV.
Thrips (order Thysanoptera) rasp plant tissue and feed on the cell contents. Western flower thrips (Frankliniella occidentalis) is the most economically damaging species. Adults and larvae both feed. They pupate in the soil.
Mealybugs are soft scale insects (family Pseudococcidae) that feed on plant sap. Females are wingless and covered in white waxy filaments. They excrete honeydew and are often farmed by ants.
Leafhoppers (family Cicadellidae) are fast-moving, wedge-shaped insects 3–15mm long that jump and fly when disturbed. They inject toxic saliva while feeding, which causes the characteristic marginal burn.
Larva of the Five-Spotted Hawk Moth (Manduca quinquemaculata). Adults lay single eggs on leaf undersides. Larvae feed for 3–4 weeks and can consume entire plants. Overwinters as pupae in soil.
Larva of the Cabbage White butterfly (Pieris rapae). Females lay single oval yellow eggs on leaf undersides. Multiple generations per season. Can devastate brassica plantings if uncontrolled.
Larva of the Looper Moth (Trichoplusia ni). Unlike the cabbage worm (butterfly larva), this is a moth larva. Adults are nocturnal and fly in from warmer regions each year — they cannot overwinter in cold climates. Multiple generations per year.
Larva of Helicoverpa zea moth. One of the most economically damaging pests in North America. Adults migrate northward each spring on wind currents. Females lay eggs on corn silks and tomato leaves.
Leptinotarsa decemlineata is one of the hardiest insect pests, notorious for developing pesticide resistance rapidly. Adults overwinter in the soil and emerge in spring when soil reaches 50°F.
Flea beetles (family Chrysomelidae) overwinter as adults in soil and leaf litter. In spring they emerge and feed heavily on seedlings. Each species prefers specific plant families — brassica flea beetles attack brassicas, potato flea beetles attack solanums.
Popillia japonica — introduced to the US from Japan in 1916. Adults emerge in early summer for 6–8 weeks. Grubs overwinter deep in soil, then move up to feed on roots in spring.
Anasa tristis overwinters as adult in garden debris. One generation per year. Nymphs and adults pierce stem tissue and inject toxin. Difficult to control chemically once mature.
Larva of a clear-winged moth (Melittia cucurbitae) that mimics a wasp. The adult moth lays single flat brown eggs on stems and leaf stalks near the base of the plant in early summer. Larvae bore inside stems and feed for 4–6 weeks.
Two species commonly damage gardens. Both overwinter as adults and emerge in spring. They are the sole vector of Bacterial Wilt (Erwinia tracheiphila), making them one of the most damaging garden pests despite their small size.
Larvae of various noctuid moths. Adults lay eggs on grass or weeds in late summer. Larvae overwinter in soil and resume feeding in spring. Tunnel into soil by day; feed at night. Most damaging in the first weeks after transplant.
Larvae of click beetles (family Elateridae). The larval stage lasts 3–6 years in soil before pupating. Adults are relatively harmless. Wireworm populations are highest in soils with high organic matter, recently cultivated from turf.
Meloidogyne species are microscopic roundworms (< 1mm) that invade young roots, causing plant cells to enlarge into galls. Females lay eggs inside the galls. Soil temperatures above 64°F promote reproduction. Sandy soils favor population growth.
Slugs (shell-less) and snails (with shell) are mollusks, not insects. They require moisture and are most active at night and on overcast days. They hide under boards, rocks, mulch, and dense vegetation during the day. Cold, wet springs favor large populations.
Earwigs (order Dermaptera) are omnivores. European earwig (Forficula auricularia) is most common in gardens. They are primarily nocturnal and hide in moist, dark areas during the day. They overwinter as eggs in soil cells.
Larvae of various flies (Liriomyza), moths, or beetles that feed between the upper and lower layers of the leaf. They are protected inside the leaf from contact pesticides. Multiple generations per season.
Larvae of noctuid moths (Spodoptera species). Fall armyworm cannot overwinter in northern US — adults migrate northward on wind each summer from Florida and the Gulf Coast. Populations can be enormous in warm years.