Two-Spotted Spider Mite

Beginner Advanced

Click to print

Click to enlarge.

Beginner

Scientific Name
Tetranychus urticae

Identification

Initially, mite feeding causes yellowing or bronzing of leaves
It can then proceed to significant defoliation, exposing fruit to the sun and birds and reducing holding ability
The farther away harvest is, the more potential impact
If populations are high, with no rain to wash them off, expect defoliation to proceed from the field edges inwards
Mites are often worse along roads where the crop gets covered in dust

Often Confused With
N/A

Period of Activity
This pest is a sporadic problem during long periods of hot, dry weather.

Scouting Notes
You may first notice a problem when you see symptoms of their feeding on the tomato leaves. Look for mites and webbing on the underside of older leaves. A hand lens is necessary to see them clearly. Tap leaves over a white paper and look for them crawling on the paper. You can spread the mites by walking through the field. Scout the areas where you do not see damage first, then the damaged areas, to avoid spreading the mites to new areas of the field.

Thresholds
None established.

Images by

David Cappaert, Some rights reserved. Licensed under a Creative Commons License.

Advanced

Scientific Name
Tetranychus urticae

Identification
The two-spotted spider mite is more closely related to spiders than to insects. It has five developmental stages:

a clear round egg;
a larval stage with three pairs of legs;
two nymphal stages, each with four pairs of legs; and
an adult stage with four pairs of legs.

Adults are extremely small and barely visible to the naked eye. The two-spotted spider mite is usually clear with two spots, but turns reddish orange in response to cooler fall and winter temperatures. They produce webbing but unlike the webbing of a spider, the underside of an infested leaf has a sandblasted appearance.

Initially, mite feeding causes yellowing or bronzing of leaves, which can proceed to significant defoliation, exposing fruit to the sun and birds and reducing holding ability. The farther away harvest is, the more potential impact. If populations are high, with no rain to wash them off, expect defoliation to proceed from the field edges inward. Mites are often worse along roads where the crop gets covered in dust.

Often Confused With
N/A

Biology
The mites overwinter as adult females in protected areas such as plant debris in hedge rows, fence rows and fields with heavy trash. The onset of warm spring weather activates the mites to search for food plants and egg laying sites. Each mated female will lay approximately 100 eggs over a 30-day span. It is not necessary for these mites to mate; therefore, it takes only one female to establish a new colony at a new location. Under ideal conditions mated and non-mated spider mites can complete their life cycle in less than a week; therefore, their population can explode in a short period of time. There can be 10 to 15 generations per season.

Two-spotted spider mites will feed on an extremely wide variety of host plants, including many grassy and broadleaf weeds, fruit crops, vegetable crops, and field crops such as soybeans and field corn. They usually feed on the underside of the leaves by piercing and sucking plant juices.

Period of Activity
Hot humid conditions with little precipitation favour spider mite outbreaks. These are often coupled with high winds which disperse the mites great distances.

When the food source of the host becomes less suitable, the non-mated female mites will begin to mass at the top of the plants. The mites are able to spin webbing, and often this webbing will serve as a balloon, allowing even small winds to pick them up and carry them for quite a distance. This explains the appearance of mites throughout a crop where none were observed a short time before.

Scouting Notes
You may first notice a problem when you see symptoms of their feeding on the tomato leaves. Look for mites and webbing on the underside of older leaves. To check for mites, sharply tap a plant against your hand while holding it over a white sheet of paper. Look for slow moving dark specks. You may need a lens to see the mites clearly. You can spread the mites by walking through the field. Scout the areas where you do not see damage first, then the damaged areas, to avoid spreading the mites to new areas of the field.