Pest description and crop damage These mites are about 4 mm long, have eight legs, and are light tan or greenish with a dark spot on each side. Spider mites feed by sucking the contents out of leaf cells, causing a mottling and bronzing of the leaves. Their feeding reduces plant vigor and may cause leaves to turn brown and drop.
Biology and life history Mites overwinter as females under loose bark or organic debris at the base of host plants, and on weeds. In the spring, they emerge, disperse, and lay eggs on the leaves. Eggs hatch into larvae in a few days. There may be multiple generations per year. The twospotted spider mite is a warm-season mite, and the greatest activity occurs under warm conditions. Depending on temperature, a complete generation may require one to three weeks. In the fall, adults cease feeding and migrate to overwintering sites.
Scouting and thresholds Infestations usually begin on lower leaves of plants, then progress upwards. Inspect oldest leaves first for stippling; webbing and the mites themselves can be found on the underside of leaves.
Rain and cool temperatures tend to suppress mite populations. Considerable natural control is provided by lady beetles and minute pirate bugs (Orius spp.). Predator mites such as Typhlodromus spp., Stethorus spp., or Neoseiulus fallacis (syn. Amblyseius fallacis) are also effective at managing populations of spider mites and may be purchased and released.
Avoid early season applications of insecticides, which reduce populations of beneficial insects. Spider mite infestations are favored by dry, dusty conditions, so avoid creating these problems and stressing the plants. Mites can be hosed from plants with a strong stream of water. Excessive nitrogen fertilization may cause population buildup.
Management-chemical control: HOME USE
- azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use
- insecticidal soap-Some formulations OMRI-listed for organic use.
- kaolin-Applied as a spray to leaves, stems and fruit it acts as a repellent to some insect pests. Some formulations are OMRI-listed for organic use.
- plant essential oils (cinnamon, clove, peppermint, rosemary, thyme)-Some formulations are OMRI-listed for organic use.
- sulfur-Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
- acequinocyl (Kanemite) at 0.2 to 0.3 lb ai/a. PHI 7 days. Gooseberry only. Controls adults, larvae, nymphs and eggs.
- azadirachtin (Neemix and other brands)-Consult label for rate. PHI 0 days. Some formulations are OMRI-listed for organic use.
- bifenazate (Acramite 50WS) at 0.375 to 0.5 lb ai/a. PHI 14 days. Gooseberry only. Also allowed in non-bearing currants (PHI 365 days). Controls adults, larvae and nymphs, and some activity on eggs.
- etoxazole (Zeal) at 0.09 to 0.135 lb ai/a. PHI 14 days. Gooseberry only. Controls eggs and young mites only; not adult mites. One application allowed per season.
- hexythiazox (Onager and other brands) at 0.09 to 0.1875 lb ai/a. PHI 7 days. Gooseberry only. Controls eggs, larvae and nymphs only; does not control adult mites. Do not exceed one application per crop season.
- horticultural oil (several brands)-Consult label for rates. Apply as a dormant spray in early season before buds open. Some formulations are OMRI-listed for organic use.
- insecticidal soap (M-Pede and other brands)-Consult label for rate. PHI 0 days. Some formulations are OMRI-listed for organic use.
- pyridaben (Nexter) at 0.2 to 0.5 lb ai/a. PHI varies by label. Gooseberry only.