Category : Insects
Beet armyworm larva
Beet armyworm eggs covered in white hairs
Singular, or closely grouped circular to irregularly shaped holes in foliage; heavy feeding by young larvae leads to skeletonized leaves; shallow, dry wounds on fruit; egg clusters of 50-150 eggs may be present on the leaves; egg clusters are covered in a whitish scale which gives the cluster a cottony or fuzzy appearance; young larvae are pale green to yellow in color while older larvae are generally darker green with a dark and light line running along the side of their body and a pink or yellow underside.
Organic methods of controlling the beet armyworm include biological control by natural enemies which parasitize the larvae and the application of Bacillus thuringiensis; there are chemicals available for commercial control but many that are available for the home garden do not provide adequate control of the larvae.
Cabbage aphid colony
Cabbage aphid colony on Brassica spp.
Colony with parasitized aphid
Large populations can cause stunted growth or even plant death; insects may be visible on the plant leaves and are small, grey-green in color and soft bodied and are covered with a white waxy coating; prefer to feed deep down in cabbage head and may be obscured by the leaves.
If aphid population is limited to just a few leaves or shoots then the infestation can be pruned out to provide control; check transplants for aphids before planting; use tolerant varieties if available; reflective mulches such as silver colored plastic can deter aphids from feeding on plants; sturdy plants can be sprayed with a strong jet of water to knock aphids from leaves; insecticides are generally only required to treat aphids if the infestation is very high - plants generally tolerate low and medium level infestation; insecticidal soaps or oils such as neem or canola oil are usually the best method of control; always check the labels of the products for specific usage guidelines prior to use.
Cabbage looper and damage
Cabbage looper adult
Cabbage looper (Trichoplusia ni)
cabbage looper feeding on leaves
Cabbage loopers egg
Large or small holes in leaves; damage often extensive; caterpillars are pale green with a white lines running down either side of their body; caterpillars are easily distinguished by the way they arch their body when moving; eggs are laid singly, usually on the lower leaf surface close to the leaf margin, and are white or pale green in color.
Looper populations are usually held in check by natural enemies; if they do become problematic larvae can be hand-picked from the plants; an organically acceptable control method is the application of Bacillus thuringiensis which effectively kills younger larvae; chemical sprays may damage populations of natural enemies and should and should be selected carefully.
Cutworm larva severing plant stem
Greasy cutworm (Agrotis ipsilon aneituma) adult
Cutworms will curl up into a characteristic C shape when disturbed
Bronzed cutworm (Nephelodes minians) adult
Cutworm feeding on plant stem
Army cutworm (Euxoa auxiliaris)
Stems of young transplants or seedlings may be severed at soil line; if infection occurs later, irregular holes are eaten into the surface of fruits; larvae causing the damage are usually active at night and hide during the day in the soil at the base of the plants or in plant debris of toppled plant; larvae are 2.5–5.0 cm (1–2 in) in length; larvae may exhibit a variety of patterns and coloration but will usually curl up into a C-shape when disturbed.
Remove all plant residue from soil after harvest or at least two weeks before planting, this is especially important if the previous crop was another host such as alfalfa, beans or a leguminous cover crop; plastic or foil collars fitted around plant stems to cover the bottom 3 inches above the soil line and extending a couple of inches into the soil can prevent larvae severing plants; hand-pick larvae after dark; spread diatomaceous earth around the base of the plants (this creates a sharp barrier that will cut the insects if they try and crawl over it); apply appropriate insecticides to infested areas of garden or field if not growing organically.
Larva feeding on cabbage leaf
Diamondback moth feeding on Brassicae
Diamondback moth pupae
Diamondback moth egg
Diamondback moth adult
Diamondback moth early instar larva
Young larvae feed between upper and lower leaf surface and may be visible when they emerge from small holes on the underside of the leaf; older larvae leave large, irregularly shaped shotholes on leaf undersides, may leave the upper surface intact; larvae may drop from the plant on silk threads if the leaf is disturbed; larvae are small (1 cm/0.3 in) and tapered at both ends; larvae have to prolegs at the rear end that are arranged in a distinctive V-shape.
Larvae can be controlled organically by applications of Bacillus thurengiensis or Entrust; application of appropriate chemical insecticide is only necessary if larvae are damaging the growing tips of the plants.
Crucifer flea beetle damage on broccoli leaf
Adults and associated damage on cabbage
crucifer flea beetle (Phyllotreta cruciferae) on Chinese cabbage.
Adult flea beetle on a leaf
Shothole" damage on chinese cabbage due to crucifer flea beetle
Small holes or pits in leaves that give the foliage a characteristic “shothole” appearance; young plants and seedlings are particularly susceptible; plant growth may be reduced; if damage is severe the plant may be killed; the pest responsible for the damage is a small (1.5–3.0 mm) dark colored beetle which jumps when disturbed; the beetles are often shiny in appearance.
In areas where flea beetles are a problem, floating row covers may have to be used prior to the emergence of the beetles to provide a physical barrier to protect young plants; plant seeds early to allow establishment before the beetles become a problem - mature plants are less susceptible to damage; trap crops may provide a measure of control - cruciferous plants are best; application of a thick layer of mulch may help prevent beetles reaching surface; application on diamotecoeus earth or oils such as neem oil are effective control methods for organic growers; application of insecticides containing carbaryl, spinosad, bifenthrin and permethrin can provide adequate control of beetles for up to a week but will need reapplied.
Large cabbage white (and Cross-Striped Cabbageworm)
Cabbageworm and frass
Cross striped cabbage worm
cabbage white (Pieris rapae) adult
cabbage white (Pieris rapae) eggs
cross-striped cabbageworm (Evergestis rimosalis) feeding on leaves
cross-striped cabbageworm on brassica
cabbage white (Pieris rapae) early instar larvae
Cabbage white (Pieres rapae): Pupa of imported cabbageworm (left) and southern cabbageworm (right).
cross-striped cabbageworm on cabbage
Cabbage white adult
Large ragged holes in leaves or bored into head; green-brown frass (insect feces) on leaves; caterpillar is green in color and hairy, with a velvet-like appearance; may have faint yellow to orange stripes down back; slow-moving compared with other caterpillars.
Hand-pick caterpillars from plants and destroy; scrape eggs from leaves prior to hatching; apply appropriate insecticide if infestation is very heavy.
Thrips (Western flower thrips, Onion thrips, etc.)
Western flower thrips
Second instar nymph (and damage to leaf) of the onion thrips (Thrips tabaci).
Onion thrips (Thrips tabaci)
First instar nymph of onion thrips (Thrips tabaci).
If population is high leaves may be distorted; leaves are covered in coarse stippling and may appear silvery; leaves speckled with black feces; insect is small (1.5 mm) and slender and best viewed using a hand lens; adult thrips are pale yellow to light brown and the nymphs are smaller and lighter in color.
Avoid planting next to onions, garlic or cereals where very large numbers of thrips can build up; use reflective mulches early in growing season to deter thrips; apply appropriate insecticide if thrips become problematic.