Description of the Pest
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 can contaminate the navels of navel oranges and sometimes mandarins, and is a 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.
Monitoring and Treatment Decisions
Protocols have been established for growers to export navel oranges free of bean thrips. For information on current protocols see the California Citrus Quality Council (CCQC) website. Be sure to read over all of the conditions of the current protocol as it is revised yearly.
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 (1 mm) long 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 and may be cut to bean thrips' length when taking slices.
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 Sticky Card Identification of Bean Thrips.) Citrus or western flower thrips in the navel can be alive through November but are normally dead after that in the San Joaquin Valley.
Green sticky traps can be helpful in detecting migrating adults. Hang the 3 x 4.5 inch 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.
For navel oranges shipped to Australia or New Zealand, follow the online "8-point plan" (see the California Citrus Quality Council [CCQC] website), and use one of the following two postharvest treatments.
- Bring the temperature in the sweat room to 65°F for 8 hours immediately prior to fruit immersion or washing.
- Fumigate the fruit in sweat rooms or apply pyrethrin/piperonyl butoxide.
|Common name||Amount to use||REI‡||PHI‡|
|(Example trade name)||(hours)||(days)|
|Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.|
|POSTHARVEST FRUIT TREATMENTS|
|(B. MGK AgriPest Cropfume PH with pyrethrins)||5 g/1000 ft3||2||NA|
|(Evergreen EC 60-6)||See comments||12||NA|
|MODE-OF-ACTION GROUP NUMBER1: 3A/—|
|COMMENTS: For use on oranges only. Dilute Evergreen EC at 1 qt per 3 gal water; fog at 1 oz of diluted product per 1000 ft3.|
|‡||Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.|
|1||Rotate chemicals with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode-of-action group numbers (un = unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee).|