Beginner

Scientific Name
Tetranychus urticae

Identification
Spider mites feed on the leaf surface, using sucking mouth parts to remove the contents of individual cells. Feeding injury causes mottling of leaves. As the damage increases, leaves turn brown or bronze, which results in reduced photosynthesis.

Mites are tiny, eight-legged creatures less than1 mm long. They are difficult to see without a hand lens. They are a translucent yellowish colour with a dark reddish-brown spot on each the side of the abdomen. The adults have 8 legs, although the first instar larvae have only 6. Mites prefer to feed on the underside of leaves. They spin fragile webs on the leaves of plants growing along the dusty borders of a field.

Two-spotted spider mite eggs are perfectly spherical and translucent yellow in colour. They are often suspended in a fine network of silk webbing. Spider mites are usually found on the lower leaf surface.

Often Confused With
Drought stress

Period of Activity
Mite activity is most common in hot, dry conditions. They often move into other crops following wheat harvest.

Scouting Notes
Examine leaves with a magnifying glass when scouting potato fields for other insects.

Thresholds
Not established. It is a sporadic pest in Ontario.

Advanced

Scientific Name
Tetranychus urticae

Identification
Spider mites feed on the leaf surface, using sucking mouth parts to remove the contents of individual cells. Feeding injury causes mottling of leaves. As the damage increases, leaves turn brown or bronze, which results in reduced photosynthesis.

Mites are tiny, eight-legged creatures less than1 mm long. They are difficult to see without a hand lens. They are a translucent yellowish colour with a dark reddish-brown spot on each the side of the abdomen. The adults have 8 legs, although the first instar larvae have only 6. Mites prefer to feed on the underside of leaves. They spin fragile webs on the leaves of plants growing along the dusty borders of a field.

Two-spotted spider mite eggs are perfectly spherical and translucent yellow in colour. They are often suspended in a fine network of silk webbing. Spider mites are usually found on the lower leaf surface.

Often Confused With
Drought stress

Biology
Occasionally, the two spotted spider mite infests potato fields. They damage plants by puncturing the leaf tissue with their mouth parts to extract plant juices.

Spider mites overwinter as female adults in crop residue or sheltered areas. In early spring, they lay eggs on grassy weeds, in fence rows and in wheat fields.  Each adult female can lay up to 100 eggs. Spider mites often move into vegetable crops as the wheat fields and other grasses begin to dry down. Under hot, dry conditions spider mites may complete a generation in as little as 6 days, resulting in numerous generations each year.

Period of Activity
Mite activity is most common in hot, dry conditions. They often move into other crops following wheat harvest.

Scouting Notes
Examine leaves with a magnifying glass when scouting potato fields for other insects.

Thresholds
Not established. It is a sporadic pest in Ontario.

Management Notes
Sporadic, no management required.