Mint-Spider mite

Includes spider mite (Tetranychus urticae)

Pest description and crop damage Spider mite adults are small, eight-legged, spiderlike animals associated with webbing and round eggs on the underside of leaves. They are pale green, yellowish to reddish, with two large, dark spots on each side of their bodies. They suck plant juices, causing leaves to yellow, dry, and fall under heavy infestations. They reduce oil yield and probably quality.

Biology and life history Mites overwinter as mature females found at the bases of mint stems and underground. In spring, feeding begins on new growth soon after emergence from soil. Populations are delayed a few weeks in fields flamed for rust in the spring. Females lay eggs associated with silk webbing. Egg to adult may take as little as 14 days during the hot part of summer. There are multiple generations each year.

Scouting and thresholds Average numbers of mites per leaf are determined throughout a field on a weekly basis. Take 45 leaf samples (three leaves per stem, 15 stems per site), and use the presence or absence of mites on leaves to estimate a mean number of mites per leaf at a site in a field. Stable and increasing populations of spider mites beginning at levels of five mites per leaf can reduce oil yields if not controlled.

Management-cultural control

Fall plowing and fall and spring flaming tend to delay spider mite buildup early in the season. These practices can also reduce predator populations whose absence sometimes allows for a more rapid spider mite population build-up in the spring than would otherwise occur.

Management-biological control

Predator mites naturally occurring in the field as well as those bought from suppliers and released into fields early in the season before spider mites reach damaging levels can maintain spider mite levels sufficiently low to avoid miticide applications. This assumes that production practices that reduce predator mites can be avoided or timed so as to reduce their negative effects.

Management-chemical control

  • abamectin (ABBA, Agri-Mek 0.15EC) at 0.009 to 0.014 lb ai/a. PHI 28 days. REI 12 hr. Do not apply more than twice consecutively or within 7 days of the first. Do not apply more than three times per crop season nor exceed 0.042 lb ai/a per season. An organosilicone surfactant increases efficacy.
  • bifenazate (Acramite 4SC) at 0.375 to 0.75 lb ai/a. PHI 7 days. REI 12 hr. One application per year only. May be applied through chemigation.
  • dicofol (Dicofol 4E) at 0.875 to 1.25 lb ai/a. PHI 30 days. REI 32 days. Do not feed treated hay or spent hay to livestock. Very toxic to predator mites. One application per season. Washington only.
  • etoxazole (Zeal) at 0.09 to 0.18 lb ai/a. PHI 7 days. REI 12 hr. Do not exceed 0.18 lb ai/a per season. Limit 1 treatment per year.
  • fenpyroximate (FujiMite 5EC) at 0.625 to 1.25 lb ai/a. PHI 1 day. REI 12 hr. Limit 2 applications per season. Do not exceed 2.5 lb/a per season. Retreatment interval 7 days.
  • hexythiazox (Onager Optek) at 0.094 to 0.156 ai/a. PHI 30 days. REI 12 hr. One application per year. SLN OR-170009; ID-170003; WA-170005.
  • malathion (Gowan Malation 8) at 0.94 lb ai/a. PHI 7 days. REI 12 hr. Limit 3 applications per year. Retreatment interval 7 days.
  • oxydemeton-methyl (MSR Spray Concentrate) at 0.1875 lb ai/a. PHI 14 days. REI 19 days. Retreatment interval 10 days. Apply in at least 20 gal water/a. Two applications allowed per year. Label allows chemigation.
  • propargite (Omite 6E, Comite) at 1.5 to 2.0 lb ai/a. PHI 14 days. REI 7 days. Limit 2 applications per year. Retreatment interval 7 days. Ground and aerial applications are allowed. Do not exceed 4.1 lb ai/a per season. Do not feed treated mint to livestock.

Note: Use of carbamate and some OP insecticides may stimulate or increase spider mite populations by killing predator mites or even stimulating spider mite reproduction. Certain miticides, even though they initially control spider mites, may result in a subsequent rapid increase in numbers due to the effect on predator mites that contribute to biological control.

Note: Utility of Metasystox-R and malathion as miticides has diminished through the years with development of tolerance and/or resistance in some mite populations.