This project sought to verify whether the diamondback moth, a major pest of collards in South Carolina, had become immune to traditional management and if so, to find IPM methods that would minimize use of chemical insecticides and maximize use of beneficial natural enemies.
Adult diamondback moth.
Collards, valued at more than $3.3 million, are the most important
crucifer grown in South Carolina and are produced not only for South Carolina,
but also for markets in Florida, Georgia, North Carolina, Virginia, Pennsylvania,
and Tennessee. Finding an effective IPM program would thus have major economic
and environmental benefits.
Microbial Insecticides Used in Past
In the past, South Carolina growers had been quick to use microbial
insecticides in the perpetual battle to manage the diamondback moth and
conserve beneficial arthropods. The most widely used of these microbial
insecticides was Bacillus thuringiensis (13t), because it was effective
against the moth in the targeted caterpillar stage but does little or no
harm to mammals, birds, and natural enemies of insect pests. Collard growers
used it for many years.
The diamondback moth, however, is noted for its
ability to survive in spite of management practices. It was the first crop
pest in the world to develop resistance to DDT when this insecticide was
considered the cure-all. It has since developed resistance to most classes
of chemical insecticides.
Lexington County, South Carolina, has the highest
collards acreage in the state, and collard growers in that county started
having serious difficulty managing the diamondback moth in the mid-1990s
despite use of Bt. In 1997, the Clemson University Extension IPM Program
funded a project to apply IPM research to this
problem.
Four-Point IPM Strategy Developed
Extension specialists and agents at Clemson, led by Mohamed F. R. Khan, Randall P. Griffin, and J. Powell Smith, used a four-point strategy:
1. Diamondback moth caterpillars were tested for resistance to Bt, and after two years of research, it has been confirmed that in Lexington County, diamondback moth caterpillars are indeed resistant to that microbial insecticide.
2. A high-priority search was carried out for new insecticides that were effective, user-friendly, and safe for natural beneficial enemies. Section 18 labels were requested for any such chemicals. Two new insecticides, SpinTor and Proclaim", have now been found to be effective in controlling diamondback moth caterpillars, and Spinosad (SpinTor) was labeled for use on collards early in 1998. Growers now use other insecticides at the action threshold and SpinTor only when there is a very high population of diamondback moth.
3. Growers would only use insecticides at the economic threshold of one larva per plant, and the insecticides would be directed against very small caterpillars and rotated.
4. Scouts were employed by growers and trained by Clemson University Extension agents and specialists in sampling and identifying insect pests, including the diamondback moth and beneficial natural enemies.
Collard growers are now allowing natural enemies
to assist them in controlling the diamondback moth. They are so encouraged
by the success of the parasitoid Diadegma insulare that some are buying
and releasing another parasitoid, Cotesia plutella, in an effort toward
sustainable management, so that SpinTor is used only when strictly necessary.
For now, growers are winning the battle, but strategies
to ensure adequate IPM for the diamond back moth must continue to be developed,
implemented, and evaluated.
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| Collards are the most important crucifer grown in South Carolina |
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A collard plant showing feeding damage by
the larvae of the diamondback moth.
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This work is supported by the Clemson University Extension IPM Program.
For more information contact:
Anthony Keinath
Department of Plant Pathology
Coastal Research & Extension Center
2865 Savanna Highway
Charleston, SC 29414-5332
(843) 766-3761
