Latin name: Tetranychus urticae
Reason for Concern:
1) An occasional pest in blackberries.
2) Reduces plant vigor, fruit yield and size by feeding on fruiting floricanes.
3) Heavy infestations can result in leaves drying up and dropping off.
4) Excessive defoliation during and after harvest from heavy feeding can reduce yield 25% the next season.
5) Mite feeding weakens primocanes, predisposing plants to winter injury.
Tiny (0.5 mm) and oval from spring to fall, they are pale yellow to green. Females have 2 large black spots on the back and sides of the body. Orange overwintering females appear in late fall and can be confused with the predatory mite, Phytoseiulus persimilis. Fine silk webbing is typically present on mite infested leaf undersides. Spider mites suck juices from the plant causing gray or whitish stippling on leaf surfaces. As the population grows and feeding progresses, leaves turn silver or bronze, then yellow-brown before drying up and falling off.
Where winters are cold, dormant adult females overwinter at the caneberry base or in weeds in or by the field. At the onset of spring, they migrate to deposit eggs on plant foliage. Eggs hatch in 1 to 2 weeks and immature mites become reproductive adults in another 1 to 3 weeks. They have 1 larval and 2 nymph stages. In hot, dry weather, a lifecycle can occur in 10 days. In mid-August, female mites overwinter. Populations increase rapidly after harvest through early fall when they move from fruiting canes to primocane foliage.
- In susceptible varieties, such as Chester, start inspecting leaves for spider mites and mite predators in late May.
- Sample at least every two weeks, more often during hot periods.
- White speckling is a sign of mite feeding. Turn over older leaves with these symptoms and examine for mites and mite predators. Use a 10 X power hand lens.
- Sample from 4 well-distributed sites per field and inspect 10 leaflets at each site. Keep records of the date, field area and sampling results for each inspection. Include spider mite adults, nymphs and eggs as well as mite predators.
- Examine for webbing between or under the leaflets. Webbing indicates a very heavy infestation.
- Damage is most noticeable in dry, dusty areas of the field, often along roadways.
- Diagnostic tools: breathe on leaflets, this causes the mites to scurry about, or tap the leaf over a white sheet of paper to make the pest visible.