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Past Articles Library | Organic Pest Control | Spidermites

THE SPIDER MITE  (Acarina)

Spider mites are found throughout North America. The two-spotted spider mite is most common. They often spin fine webs on leaves. To make sure your plant has spider mites, take a white piece of paper and sharply knock the stem on which they are living. If it is mites, you will see little specks moving around on the white paper.

DESCRIPTION

Adults are extremely small, 1/75-1/50 of an inch, with eight legs. They are related to the spider family and have fine hairs, which can be reddish, light green or yellow, covering their bodies. Most spider mites spin webs on leaves and shoots, but not all species do this.

LIFE CYCLE

Adults and eggs overwinter in crevices in the bark or in garden debris. Eggs hatch in 1-8 days, and nymphs develop into adults in 5-10 days. Both adults and early nymphs emerge in the spring. Reproduction continues year-round on houseplants and in greenhouses.

PLANTS MOST AFFECTED

Many vegetables, including cucumbers, eggplant, bean, tomato, and melon. Fruit trees, houseplants and ornamentals, like the Monterey Pines shown to the left are susceptible.

DAMAGE

Both adults and nymphs pierce the plant and suck the juice from the underside of the leaves. This weakens the plant, causes leaves to drop, and stunts fruit. Damage first appears as yellow speckled areas on leaves; extremely fine webbing sometimes is visible on the underside of the leaves. Spider mite outbreaks can be severe and rapid in hot, dry conditions; in low humidity, the mites feed more to avoid drying up.

MEANS OF CONTROL

Organic Control: Spray dormant oil on fruit trees to kill overwintering eggs. In gardens or green houses, rinse the infected plants with water and mist them daily to minimize reproduction. Release predatory mites. Check with the local suppliers to see which species of predatory mites is best for your conditions, since there are many species of predatory mites. Spray insecticidal soap or neem oil. Chemical Control: Spray with Pyrethrum, Rotenone, or Orthene.