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Pink bollworm control: greatest environmental story seldom told

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  • The San Joaquin Valley escapes wrath of world's most destructive cotton pest for four decades thanks to the effort of thousands.

I wrote many screwworm articles when I was a reporter on a couple of West Texas dailies and the Tucson (Ariz.) Daily Citizen. Some of those articles detailed health officials finding screwworms feeding on humans. It also was common in dogs and cats.

There was no way to spray insecticides over the vast expanses of the arid West to control screwworm. USDA-ARS entomologists Ed Knipling and Ray Bushland developed a sterile insect technique that exposes lab-reared screwworms to low doses of radiation to make them sterile. These sterile flies are aerially released to mate with fertile females. The result is no eggs develop. It is an amazing biological control technique.

This technology was employed to not only drive screwworm out of the U.S, but drive them all the way to the Isthmus of Panama where there is a sterile release barrier to block any re-migration north.

Scientists determined that this same technology could be utilized to keep pink bollworm out of the San Joaquin. With federal grants and grower money funding, a pink bollworm rearing facility was built in Phoenix. It was first located in trailers on property owned by Arizona cotton growers and later a permanent rearing facility funded by California cotton growers that is still in operation and the key to eradicating the pink bollworm in Arizona, New Mexico and Texas, Southern California and Northern Mexico.

Millions of pink bollworms are raised in that facility and packaged for shipment to areas where they are loaded on planes and dropped on cotton fields. This has been going on for more than four decades in the valley and now employed as part of the eradication effort.

California cotton growers are assessed annually to support this program, which includes extensive mapping of cotton fields and pheromone trapping. These traps catch both sterile and, if there are any, native moths. This is how program leaders know if the sterile moths are working. The PBW threat has never gone away in those four decades. Migrating native PBW moths have been trapped in the deserts between Southern California and the southern San Joaquin over the years.

Hot spots have been identified in the past where trap catches of native moths indicate possible infestations brewing. This triggers higher sterile moth drops in the area and possible treatment with pheromone impregnated fibers to disrupt mating of native moths.

Another key to this exclusion/control process is preventing overwintering of PBW. Cotton growers are required to shred and bury cotton residue after harvest to create a winter-long host free period. SJV growers cannot plant cotton until March 10 to maintain that host free period. Arizona growers utilize the same PBW management practice.

Arizona has survived the pink bollworm for decades, but it has been a costly fight. They started to rid themselves of the insect pest with the introduction of Bt cotton. This remarkable technology slashed pesticide and pheromone costs and opened the door to eradication.

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