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 are a problem in the San Joaquin Valley and interior districts of Southern California. Bean thrips don’t directly damage fruit or reproduce on citrus, but they can contaminate the fruit, which is a concern to some trading partners. Overwintering adult bean thrips come out of multiply on weed vegetation from March to September. Bean thrips migrate into citrus groves in fall (September to October), when their weed hosts dry out and die, or the field crops they infest are harvested. They seek out green vegetation and protected areas for overwintering. Bean thrips may enter the navel of oranges and some mandarin varieties, where they overwinter from November to March and contaminate harvested fruit. This quarantined pest may cause infested fruit to be fumigated with phosphine in California or fumigated with methyl bromide at destination by some foreign countries.
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 by 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.
Pre-shipment phosphine fumigation is a mandatory treatment to ship navel orange and mandarins to Australia or New Zealand. Follow the CA Citrus to Australia Compliance Checklist (see the California Citrus Quality Council website). Fumigation facilities must be certified by the Citrus Administrative Committee, the California Department of Food and Agriculture, the California Department of Pesticide Regulation, or the United States Department of Agriculture (see the Fumigation Facility Certification Document).
- The Phosphine fumigation schedule for bean thrips is a 12-hour fumigation at temperatures of 41°F to 50°F (5°C to 10°C) at concentrations of 260 to 1,000 parts per million.
- Packaging used must be permeable to phosphine gas.
- Fumigation must follow USDA and label guidelines and applicators must maintain a fumigation logbook.
- Fumigation must be carried out by or under the supervision of certified applicators.
- Notify Country Agricultural Department 24 hours in advance for all treatments.
|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|
|(2% phosphine)||260–1000 ppm||See label||NA|
|(99.3% phosphine)||200–2500 ppm||See label||NA|
|MODE-OF-ACTION GROUP NUMBER: 24A|
|COMMENTS: For use on oranges and mandarins destined for Australia or New Zealand. Fumigate at temperature of 41°F or higher, under sealed structure.|
|‡||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.|
|*||Permit required from county agricultural commissioner for purchase or use.|