Determining which thrips species are responsible for various types of damage to stone and pome fruit

Western flower thrips (WFT), F. occidentalis, is the primary cause of thrips damage to fruit.  Host plants in and around orchards provide a constant source of infestation.  WFT enter flowers before and after they open to lay eggs and feed.  Eggs are also laid in young fruitlets during fruit set.  Feeding damage occurs on ripening fruit shortly before harvest when population levels are high.  WFT oviposition sites on ovaries in flowers and on small fruitlets develop into small pits and/or pansy spots.  The pits grow larger as the fruit develops and several such pits can occur on a single fruit.  Feeding sites on fruitlets develop into russeting damage on mature fruit, while feeding on ripening fruit results in silvering.

WFT management can be improved by commencing with monitoring before flowers reach the balloon stage.  If WFT are detected, particularly in orchards with a history of thrips damage or when warm, dry spring weather is prevalent, chemical control should be applied before flowers open, provided it is safe for pollinators.  Cover crops and/or flowering weeds should not be disturbed during flowering and fruit set, as this can result in mass migration of thrips into fruit flowers.  A photo identification chart for thrips occurring in orchards is being prepared for release in January 2009.

WFT management cannot be aimed at eliminating thrips from orchards.  A management strategy that focuses on deterring or repelling thrips from flowers, fruitlets and fruit to prevent oviposition and feeding damage would be more sustainable and would satisfy market demands for residue-free fruit.