Helping Chinese farmers step off the pesticide treadmill
Ten years ago, China had plenty of workers to hand weed their farmland, but with fewer young people choosing farming as a profession, the country is looking for quick chemical fixes to their pest management problems. UC IPM Advisor Anil Shrestha visited China to convince them that integrated pest management is by far the better long-term choice.
The International Executive Council, a nonprofit organization sponsored by the U.S. Department of Commerce, was looking for a weed expert to help China with its weed problems. Last November, Shrestha, a weed ecologist, was invited by the organization to travel to Beijing and Feidong County in Anhui province, south China.
"Traditionally, the country has relied on a hand weeding system, but with so little manpower, they have resorted to herbicides for the last decade," says Shrestha. "The country has little access to many herbicides, and, as a result, growers use only two herbicides continuously. They needed help to identify weed species that were escaping the herbicides."
Shrestha looked at other areas where Japanese foxtail was being controlled by a grass herbicide. But in this particular location, the herbicide was not controlling foxtail, even when farmers used three to four times more than the recommended rate.
“Although I couldn’t positively determine if the foxtail was resistant to the herbicide without doing a test, it seemed highly likely that it was since Japanese foxtail has developed resistance to this herbicide in other parts of the world. I feel that Chinese farmers need to be reminded that IPM is important, and here was this perfect example of suspected herbicide resistance to show them.”
Shrestha says that big clods on the farmland’s soil surface shielded weed seedlings from the herbicide. Foxtail also seemed to have a long window of emergence, and weed seedlings were emerging after the fields were already treated with herbicide.
“The geranium invasion resulted from a lack of knowledge of what herbicides to use to control them,” says Shrestha. “I suggested some products that could be used, as well as information about how these invasions occurred. One thing that I found striking was that they were very interested in using only chemical control.”
The county extension office there asked Shrestha to give a seminar on ecological weed management. More than 50 extension personnel attended the workshop where he discussed IPM techniques such as better crop rotations, fallowing, (leaving a field without crops for a season or two to get rid of all emerged weeds) varying crop seeding times, and tillage (preparing land for crop planting by plowing or disking).
During the eight days he spent in China, Shrestha gave three lectures on the importance of research-extension linkage, herbicide resistance, and ecological weed management and IPM. Shrestha also visited no-till fields and discussed potential pitfalls of transitioning to no-till systems such as shifts in weed species, initial increase in weed densities, and development of herbicide resistance if a single herbicide is used continuously.
“One goal voiced by every government person I talked with there is a concern for food security,” says Shrestha. “To compete globally and combat their manpower migration to urban areas, they are resorting to pesticides. They want to modernize their farming practices and are looking at ways to enter chemical agriculture. However, they lack the infrastructure that we have here in the U.S. They still need a strong research-extension linkage, and if they are interested in chemical farming, their greatest priority should be on pesticide safety.
“Chinese farmers know about traditional pest control, but this seems to be slowly eroding as they move toward chemical farming,” says Shrestha. “On the other hand, in the U.S., we’re moving toward ecological agriculture and revisiting some of the ecologically sound, traditional practices.”
Shrestha says we should not get too complacent in the U.S. because we practice eco-friendly approaches. “To prevent a global catastrophe, we need to visit underdeveloped countries and help them to create IPM systems that will benefit globally. Many of our food products are imported from China, so it is in our best interest that they produce food in a safe manner there.”
On a foreign exploration trip through seven Caribbean Islands and the Gulf of Mexico last March, Phil Phillips, UC IPM advisor for the Central Coast, and colleague Mark Hoddle, determined that the avocado lace bug is not native to the Caribbean, as previously believed, but to tropical Mexico. This provides a focus for efforts to find the bug’s natural enemies for biological control.
The innate lethargic behavior of ALB, which doesn’t try to escape from potential threats by flying, jumping, running, or other rapid movement, suggests that ALB may use a chemical defense strategy to repulse potential natural enemies.
“With the introductions of Persea mite (early 1990s) and avocado thrips (1996) in recent years, the California avocado industry, with a robust production history based on biological control of arthropod pests, is concerned about new pest introductions,” says Phillips. “The introduction of new exotic pest species threatens the biological underpinnings of stable IPM programs.”
To understand more about the biology, origin, and possible natural enemies of the California population of ALB, the California Avocado Commission funded a foreign exploration trip into the Caribbean, the supposed origin of ALB, and Mexico. Phil Phillips and entomologist Mark Hoddle from UC Riverside traveled through the Caribbean Islands and the Gulf Coast of Mexico over a three-week period in March 2006.
Continued >> On a prior trip to the Dominican Republic, Phillips and Hoddle had noted extensive damage and leaf drop from high populations of ALB in both backyard and commercial avocado plantings. Leaf damage consists of large tan to brown necrotic areas on the undersides of the leaves. Florida has reported similar ALB populations and damage, and scientists there suspected the origin of ALB to be somewhere in the Caribbean.
Hoddle and Phillips were successful in locating ALB in Jamaica, Puerto Rico, St. Thomas and St. John. University of the Virgin Islands Cooperative Extension personnel confirmed its presence in St. Kitts (U.S. Virgin Islands), but not in Barbados, Trinidad, or Tobago.
“The populations found attacking avocados in the northern Caribbean were all very damaging and out of control,” says Phillips. “No significant biological control was observed, nor were any egg parasitoids recovered from samples sent through quarantine at UC Riverside during the trip. On the final leg of the trip through Veracruz, Mexico, ALB was observed in considerably smaller densities, with not all avocado trees being attacked. Other than ants, no specific biological control agents were observed, and, again, egg samples sent through quarantine yielded no parasitoids.”
Based on these preliminary field observations, researchers believe that ALB is not native to the Caribbean, but to tropical Mexico. Follow-up genetic studies on the material collected during the trip should provide a more definitive answer to the question of origin.
Phillips and Hoddle continue to explore the origin and natural enemies of this pest.
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