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09
Aug

Biological Pest Controls Combat Citrus Disease after Pesticide Failure

(Beyond Pesticides August 9, 2013) Citrus growers in California are now turning to a natural solution after pesticides have been shown to be ineffective. Teams of invasive species experts have started releasing tamarixia radiate, a tiny parasitic wasp, to control the invasive Asian citrus psyllid population. Asian citrus psyllid can spread a disease which causes greening, devastating citrus production. This use of biological pest control demonstrates that the use of toxic chemicals is unnecessary as safer alternatives have already been proven effective.

California’s citrus production is a $2 billion industrWasps used to fight citrus greeningy, which accounts for 80% of the U.S. fresh market produce and after Asian citrus psyllid was detected in southern California in 2010 growers have spent close to $15 million yearly to fight this pest. The psyllids were first discovered in Florida in 1998 and has since spread to all of its 32 citrus growing counties. The United States Department of Agriculture (USDA) has quarantined nine states, including California and Florida. The quarantines prohibit interstate movement of citrus trees and require labeling of citrus nursery stocks from areas where greening has been detected.

The psyllids cause greening by spreading a disease known as Huanglongbing (HLB) to citrus trees. A pysllid that is infected with HLB can transfer the bacterium every time it feeds on the tree. Once a tree is infected with the disease there is no known cure. HLB is one of the most severe plant diseases in the world and can affect any variety of citrus trees. The disease can lie dormant for several years before tests are able to detect it. In California, the disease was first detected in November 2012 and has only been found in nine counties that are south of the commercial growing areas, but because of this dormancy California commercial operations may already be infected. After trees become infected fruit from these trees is not suitable for consumer markets because of its green color, misshapen appearance, and distinctly bitter taste.

Since 2011, teams of invasive species experts have released more than 75,000 tamarixia wasps across southern California to combat the pysllids. In 2012, agricultural officials halted pesticide spraying in Los Angeles County because it proved ineffective. Six out of 10 trees in the county grow in backyards which if pesticides were used could lead to high levels of pesticide exposure for urban environments. To curb pysllids, teams of invasive species experts have been going to individual homes, releasing the wasps, and tracking the parasites success.

The wasps are imported from Pakistan’s Punjab region and extensive tests were conducted to make sure that the wasp would not disrupt other California species or become yet another invasive species. The wasps curb pysllid populations by wasps laying eggs inside the psyllid nymph’s stomach. As the eggs hatch, larvae slowly eats away at the nymph. The teams hope that after the wasps hatch they will fly to neighboring trees and lay eggs in new nymphs and establish a growing population. Even though the team is only about a year and a half into this effort, at some release sites the population of psyllids has dramatically declined. Mark Hoodle, Ph.D., an invasive species expert at UC Riverside, said to the Los Angeles Times, “We have no other choice except to use this natural enemy or do nothing. And the ‘do nothing’ option is unacceptable.”

Beyond this recent use of tramarixia wasp, there are many other examples of effective pest management through biological controls. Last summer, several counties in New Jersey used crustaceans, which are voracious predators of mosquito larvae, to control West Nile Virus. The most effective copepod species have the capacity to kill more than 40 mosquito larvae per copepod per day, typically reduce mosquito production by 99-100%, and can maintain large populations so long as there is a reliable water source. A report in 2007 found that Muscidifurax raptor, another parasitic wasp, was effective in controlling fruit flies in vineyards. Goats have also been used across the country to weed airports, cemeteries, and to restore soil and improve land quality. The uses of biological controls are important because they prove there are alternatives to toxic pest management.

Farm operations that are USDA certified organic already avoid the use of toxic chemicals by implementing organic systems plans that can include biological pest management. To learn more about the practices and management strategies of organic agriculture, please visit Beyond Pesticides’ Keeping Organic Strong page.

Source/Image Source: LA Times

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

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One Response to “Biological Pest Controls Combat Citrus Disease after Pesticide Failure”

  1. 1
    Robert Walther Says:

    Contrary to the statement that citrus growers in California are using the parasitoid tamarixia, no grower is releasing this insect for ACP management. The only releases of tamarixia have been in urban locations. There are several commercial insectaries that are willing to rear tamarixia right now. However, the USDA, CDFA and academia want to study this for at least 3 years before taking a stance on the viablity of integrating tamarixia into a pest management program. Where eradication of ACP is not possible, IPM programs utilizing tamarixia should be encouraged, NOW, not 3 years from now! Where ACP is established, permits required of the insectaries should be granted. Mass rearing of tamarixia by commercial insectaries is the only way to get the volume needed for augmentation programs. The researchers have shown us that the imported tamarixia eats California ACP. The citrus industry should now be allowed to figure out how to best utilize this wasp.

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