How to Manage Pests
UC Pest Management Guidelines
DESCRIPTION OF THE PEST
European red mites overwinter as eggs at bases of buds and spurs on smaller branches and twigs, or in wounds. Eggs are globular and red with a slender stalk (stipe) rising from the top center. During the growing season, eggs are laid on leaves. There are three instars before the adult stage. Immature mites are bright red, except just after molting when they appear bright green. The green color turns to red after the mites resume feeding. Adults are dark red and have white spots at the base of six to eight hairs on the back.
The feeding of European red mites on leaves causes the leaves to lighten in color and become mottled or stippled. Prolonged feeding by heavy populations eventually causes leaf bronzing, and under high temperatures portions of the leaf blade or its entire surface may turn brown and dry. This kind of damage, referred to as mite burn, can occur even after mites have been controlled if high temperatures occur soon after mites are controlled.
European red mite occasionally becomes troublesome in pear orchards. Dormant oil treatments and natural enemies usually keep them below damaging levels. Monitor during the season to assess need for treatment.
If European red mite populations are reduced to low levels by treating with oil during the dormant season, predators usually can effectively maintain these low levels during the growing season. Minimize the use or dosages of materials disruptive to predators, especially predaceous mites. Major European red mite predators include green lacewings, brown lacewings, minute pirate bugs, and the predatory mite Zetzellia mali.
Minimize the potential for mite problems by reducing dusty conditions within the orchard.
Organically Acceptable Methods
Biological and cultural controls and approved oil sprays are organically acceptable methods.
Monitoring and Treatment Decisions
Dormant to delayed-dormant period
Apply a dormant or delayed-dormant oil spray yearly. Sample during dormancy to determine overwintering population levels of this pest: collect 100 fruit spurs, one from the treetop and one from eye level of 50 trees in a 20-acre block. Use a 10 or 14X hand lens to examine the bases of buds and spurs. If more than 10% of the spurs are heavily infested, monitor European red mite throughout the growing season. If less than 10% of the spurs are infested, European red mite probably won't be a problem in the coming year, provided the dormant oil treatment was properly applied. If no dormant treatment was applied, European red mite should be monitored throughout the growing season if three or more spurs are infested in the sample of 100. For information on monitoring other pests at this time, see DORMANT/DELAYED-DORMANT SAMPLING.
Finger bud to petal fall
Sample again after egg hatch, usually during the period from finger bud to petal fall, by examining 100 flower clusters, one from the treetop and one from eye level, of 50 trees. If more than 5 clusters are infested, treat with oil immediately. If more than 10 are infested, add a miticide to the oil. If between 1 and 5 clusters are infested, adding oil to the first codling moth spray may be adequate. For information on monitoring other pests at this time, see SAMPLING AT BLOOM.
European red mite infestations can begin either in the tops or bottoms of the tree canopy. To detect populations, take two samples in each of 20 trees: one from the top of the tree (in spring these are spur samples and later are shoot samples) and one shoot sample from eye level. Examine five leaves per shoot. If 10 or fewer European red mites or eggs are found per 100 leaves sampled, don't treat. If 11 to 50 European red mites or eggs are found, treat with oil. If more than 50 European red mites and eggs are found, add a miticide with the oil. For information on monitoring other pests at this time, see SAMPLING DURING FRUIT DEVELOPMENT.
Continue monitoring European red mite when monitoring shoot samples for pear psylla and twospotted spider mites. Examine five leaves from each of the 20 top shoots with a hand lens (10 to 14X) and count the number of European red mites. Use the above thresholds to determine treatment needs if only European red mite is present. If both twospotted and European red mites are present, use the thresholds given in WEBSPINNING MITES.
Harvest and postharvest
Sample again during harvest and following harvest. Use the lower thresholds listed below when predators are absent to determine if a postharvest treatment is required.
UC IPM Pest Management Guidelines:
Insects and Mites
L. G. Varela, UC IPM Program, UC Cooperative Extension, Sonoma County