Latin name: Tetranychus urticae
Reason for Concern:
1) A serious pest in raspberries.
2) Feeding on fruiting floricanes reduces plant vigor, yield and size.
3) Heavy infestations can result in leaves drying up and dropping off.
4) If uncontrolled, excessive defoliation during and after harvest from heavy two spotted mite feeding can reduce yield 25% the following season.
5) Mite feeding can also weaken primocanes, predisposing them to winter injury in areas of cold winters and reducing future yields.
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.
Dusty conditions will create a larger mite population, causing more problems. Injury can be worse after harvest.
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.
- Start in early May. Sample minimum of 4 sites, 40 leaflets total.
- Adjust frequency of sampling dependent on weather, population dynamics, population life cycle, and predator population. In hot weather or locations, monitor more frequently (every 3 days) if found in an area with absence of predators.
- White speckling on leaves 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.
- 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. This indicates a high level of 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.
- Populations can increase rapidly after harvest through early September. Most of the mite population by this time has moved gradually from fruiting canes to primocane foliage.
- Usually, by mid-August, female mites begin to enter their "overwintering" red stage, with additional feeding damage to foliage minimized.