Two-Spotted Spider Mite
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.