How to Manage Pests
UC Pest Management Guidelines
Adult bean thrips have a uniformly dark, grayish black body. Their forewings have two dark and two pale bands, and (visible under magnification) the legs and antennae are also banded light and dark.
Bean thrips is a problem in the San Joaquin Valley and interior districts of southern California only because it may be considered a contaminant of the navels of navel oranges and so be of concern to some trading partners. Bean thrips migrates into groves in fall, when its weed hosts die or field crops it infests are harvested. Bean thrips enter the navel of oranges, where they overwinter and contaminate harvested fruit. This quarantined pest causes infested fruit to be fumigated with methyl bromide by some foreign countries. Bean thrips does not directly damage fruit or reproduce on citrus.
Keep orchards and bordering areas free of weed hosts to reduce bean thrips movement to citrus fruit. Where host crops (alfalfa, beans, cotton, grape, lettuce, and tomato) are grown nearby, navels are at increased risk from contamination by bean thrips. Weed hosts include filaree, malva, prickly lettuce, Russian thistle, sowthistle, tree tobacco, and grasses, especially perennial grasses.
and Treatment Decisions
Cutting Fruit. When monitoring fruit on trees, collect oranges from the lower canopy of outer rows. To detect bean thrips, cut the fruit into thin slices, starting at the navel end of the fruit, until the fruit has been sliced up to the bottom of the navel. It is easier to spot the bean thrips if the orange slices are placed on a white or blue background. Examine the slices using magnification, such as a hand lens or a hands-free magnifier. Bean thrips are about 0.04 inch long (1 mm) and to the naked eye they appear blackish with banding. Be sure to differentiate the blackish bean thrips from small pieces of the fruit stamen, which are also dark in color.
Citrus and western flower thrips may also occur in the navel, but they are usually yellowish except for the dark phase of western flower thrips, which are larger and more hirsute (longer, darker hairs) than bean thrips (see "Bean Thrips Identification - Sticky Cards").
Detecting adults. Green sticky traps have proven to be effective in detecting migrating adults. Hang the 3 x 4.5" traps in trees on one of the two outside rows of the block about 4 to 5 feet above ground (to minimize splash from irrigation and rainwater) on the side of the tree facing the outside of the block. If the outside row borders a dusty drive, use the second row from the outside of the block. Use 1 trap for every 5 acres with a minimum of 4 traps per block, one each on the north, south, east, and west sides of the block.
UC IPM Pest Management Guidelines: Citrus