Thrips are small insects (1 mm long) that overwinter as adults in weeds, leaf litter and soil. In spring, the adults fly to flowering plants like stone fruit. Typically, western flower thrips are white and yellow, except for slight brown spots or blemishes on the top of the abdomen. However, in the spring after overwintering, the dark brown form of western flower thrips may be present.
In early spring, if overwintering sites are disturbed or dry up, thrips migrate to flowering trees and plants and deposit eggs in the blossoms. When the eggs hatch, the larvae (<1 mm long) feed with their sucking mouthparts (not chewing) on the developing fruit and cause deformities, making the fruit unmarketable.
Thrips can be found inside the shucks of developing nectarines and occasionally peaches, where they can cause crescent-shaped scars that remain conspicuous at harvest. Late season feeding causes “silvering”, more conspicuous on the blush side of fruit.
Entrust, Success and Harvanta are labeled for suppression of thrips in stone fruit in Canada. In addition, Delegate plus oil, applied for first generation Oriental fruit moth, either pre-bloom or at petal fall, has been very effective. Do not make insecticide applications during bloom. A spray at petal fall will still be effective. Some thrips species quickly develop resistances to insecticides. If pressure from thrips becomes severe enough to warrant insecticide applications, it is important to rotate the classes, utilizing different Modes of Action.
Through a project funded by Niagara Peninsula Fruit and Vegetable Growers Association, Ontario Tender Fruit Growers and agri-chemical companies, we are working on identifying the thrips species present in Ontario orchards, their development, and potential management strategies.
There’s some question as to whether the warty looking nectarines we’ve seen in the past are the result of physiological responses of the young fruit to cool, wet bloom periods or to thrips injury. Side-by-side blocks have had different degrees of damage with the same spray schedule, and the same weather conditions. Cool wet weather promotes the retention of shucks where thrips hide and feed so we’ve assumed they were the culprits – a real chicken vs egg conundrum. We’ll be looking into this as well.
