Notes on Strawberry Insects
Two-spotted spider mite

Identification

Use a 10-14× magnifying hand lens to see mites properly. Overwintering adults are orange in colour. Otherwise, adult mites are 0.3-0.5 mm and greenish yellow with two dark spots on the back. Nymphs are similar in appearance only smaller. Eggs are clear and round. All stages occur predominantly on the lower leaf surface.

Two-spotted spider mite

Period of activity

Female two-spotted spider mites overwinter in crop debris on the ground. In spring they move to new growth and feed on leaves closest to the ground. There are many generations per year; eggs, nymphs and adults are frequently present at the same time. As populations build and leaves age or become damaged, mites move up the plant to newer, more succulent growth. The time for one generation to develop, from egg to mature adult, ranges from five days at 24ºC to three weeks at 12ºC.

Monitoring and thresholds

Strawberries grown in high tunnels or greenhouses are more likely to develop mite problems. Most field-grown strawberry plantings will not have a problem with mites. However, certain varieties like the day neutral variety Seascape are especially susceptible to mites. Mite outbreaks are likely related to overwintering conditions, variety, insecticides applied and the build-up of mites on adjacent crops, such as soybeans or apples.

Observe plants weekly for signs of mite damage when plants begin to grow in spring. Damage first appears as flecks and stipples on the leaves. Collect leaf samples from fully mature, but not the oldest, leaves and examine the lower surface for all stages of mites. Record the number of mites per leaflet, as well as the presence of beneficial insects such as syrphid larvae, ladybird beetle larvae and predatory mites. A leaflet is one trifoliate of the entire leaf.

A presence or absence technique can be used to reduce sampling time for mites. If 25% of leaflets have mites, the population is approximately five mites per leaflet. If 50% of leaflets have mites, the population is approximately 20 mites per leaflet.

Management notes

Several thresholds have been suggested for mite control on strawberries, ranging from 5-20 mites per leaflet. Consider these thresholds and apply miticides if damage is evident and populations increase from week to week. Beneficial insects reduce the need for miticides. There are several miticides available for strawberries. Apply each product when most mites are at a susceptible stage for that product. See Table 8-22. Miticides Registered on Strawberries. Use different products from year to year to prevent the development of resistance.

Predatory mites that feed on spider mites are available from commercial suppliers. See Pest Monitoring Equipment Suppliers. Amblyseius species are more likely to survive in field conditions. Persimillous is better in greenhouse conditions. Beneficial mites must be introduced before large populations of spider mites develop but after insecticides for tarnished plant bug have been applied. Pyrethroids, such as Decis, Matador, Cymbush and Ripcord, and Thiodan are toxic to beneficial mites.

Learn more...

• Table 8-22 - Miticides Registered on Strawberries
• Pest Monitoring Equipment Suppliers
• Notes on Strawberry Diseases and Insects
• OMAFRA Publication 360 Strawberry Calendar (non-bearing)
• OMAFRA Publication 360 Strawberry Calendar (fruiting years)
• OMAFRA Publication 360 Fruit Production Recommendations
• OMAFRA Berry Crops Index page
  

| Top of Page |