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Ministry of Agriculture, Food and Rural Affairs

Two-Spotted Spider Mite

Two-spotted spider mite Two-spotted spider mites and eggs Spider mite damage
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Beginner

Scientific Name
Tetranychus urticae

Identification

  • The adult mite is approximately 0.5– 1 mm (1/50- 1/25 in.) in length
  • It is a translucent-yellowish colour with two dark spots on the sides of its abdomen
  • Spider mites feed through sucking mouth parts
  • Injury first appears as a bronzed, stippled effect
  • Severe feeding causes curling and drying of the leaves

Often Confused With
Drought stress

Period of Activity
Mite activity is most common in hot, dry conditions. They often move into cucurbits (especially watermelons) following wheat harvest.

Scouting Notes
Carefully inspect 10 groups of 10 plants across the field.  Look for “bronzed” leaves and for signs of webbing, eggs or mites on the lower leaf surface.  If spider mites are present, record the percentage of plants infested and the severity of the infestation.  Re-visit the field over a 3-5 day period to determine if the mite population is increasing.

Thresholds
None established. Melon plants are most susceptible to damage prior to first harvest.

Advanced

Scientific Name
Tetranychus urticae

Two-spotted spider mites are mainly a pest of watermelons, however in hot, dry growing seasons they may become a problem in any cucurbit.

Identification
Spider mites are 0.5 to 1 mm (1/50- 1/25 in.) in length, and barely visible to the naked eye. 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. 

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.

Spider mites feed on the leaf surface, using sucking mouth parts to remove the contents of individual cells. This results in a stippled, bronzing effect on the leaves.  Severe feeding injury causes the leaves to become necrotic and puckered. 

Often Confused With
Drought stress

Biology
Spider mites over winter 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 cucurbits (especially watermelons) following wheat harvest.

Scouting Notes
Carefully inspect 10 groups of 10 plants across the field.  Look for “bronzed” leaves and for signs of webbing, eggs or mites on the lower leaf surface. If spider mites are present, record the percentage of plants infested and the severity of the infestation. Re-visit the field over a 3-5 day period to determine if the mite population is increasing.

Thresholds
None established. Melon plants are most susceptible to damage prior to first harvest.

Management Notes

  • Fields adjacent to wheat, edible bean or snap bean fields may be at higher risk of infection.
  • Watermelons are most susceptible to spider mite damage during fruit sizing. 
  • A heavy rain or overhead irrigation will often reduce mites to tolerable levels.