A BROAD RANGE of these agricultural technologies were discussed in presentations that focused on the use of environmentally friendlier natural and synthetic compounds for pest control, production of chemicals from biomass, light harvesting in plants by chlorophylls, and bioremediation of chemicals in soils by plants.

Green chemistry is perfect for the agriculture industry to explore real-world environmental problems and help find solutions, added David E. Barnekow, a senior scientist at Dow AgroSciences, Indianapolis. "Modern agriculture is focused on the design of chemicals formulated to be applied at lower rates as well as to be less environmentally persistent, less toxic, and more selective," he said.

	SOMETHING FISHY Oscillatoria perornata, a blue-green alga (bottom), produces 2- methylisoborneol, a terpene that gives farm-grown catfish an undesirable musty flavor. USDA researchers have found a plant-derived algicide--a proprietary anthraquinone derivative--that could replace synthetic compounds used to control algae in aquaculture.
	PHOTOS COURTESY KEVIN SCHRADER/ARS

One example Barnekow outlined is Dow AgroSciences' nitrapyrin-based nitrogen stabilizers that make more efficient use of fertilizers by reducing leaching or decomposition in the field. Another example he noted is Dow AgroSciences' Sentricon termite-control system. Sentricon uses outdoor bait stations that contain hexaflumuron, a halogenated benzamide, which inhibits the synthesis of chitin during the termites' exoskeleton molting process. In 1994, hexaflumuron became the first pesticide registered under EPA's reduced-risk pesticide initiative, and the Sentricon system earned Dow AgroSciences a 2000 Presidential Green Chemistry Challenge Award.

In a subsequent lecture, entomologist James E. Dripps from Dow AgroSciences elaborated on the development of spinosad, a natural-product pesticide. Spinosad's active ingredients, spinosyn A and spinosyn D, are produced by the soil bacterium Saccaropolyspora spinosa. There are 22 natural spinosyns that vary in activity against insect and mite pests, Dripps noted. Although a mode of action is not clear, the spinosyns appear to disrupt insect nicotinic and -aminobutyric acid receptor function.

In field tests, Dow AgroSciences' spinosyn-based products have been shown to not leach, to not be environmentally persistent, and to have low mammalian toxicity. The pesticide acts on caterpillar pests that attack cotton, fruits, vegetables, and other plants but does not harm beneficial insects, such as ladybugs. These advantages earned these products EPA's reduced-risk pesticide designation, and spinosad earned Dow AgroSciences a 1999 Presidential Green Chemistry Challenge Award.

Quantitative structure-activity relationship analysis of the spinosyns has now led to the synthesis of several hundred semisynthetic spinosoids, Dripps added. Several of these compounds are more active than spinosad but are less stable in sunlight. The company is now exploring how to improve their stability.

The U.S. Department of Agriculture, through its Agricultural Research Service (ARS), has quite a few research initiatives under way to address environmentally friendlier pest management, as several symposium speakers in Orlando related. For example, ARS's Natural Products Utilization Research Unit, University, Miss., is focusing on identifying natural products to replace synthetic pesticides, according to research leader Stephen O. Duke.

One of the projects that Duke discussed was work by microbiologist Kevin K. Schrader to find an alternative to synthetic algicides for controlling blue-green algae in catfish aquaculture ponds. Schra-der presented his work during a session on aquaculture in the Division of Agricultural & Food Chemistry.

Some blue-green algae, such as Oscillatoria perornata, produce 2-methylisoborneol, a terpene that accumulates in catfish to give them an undesirable musty flavor. Copper-based products and Diuron, a urea-based weed killer, are currently used to control algae, Duke noted. However, these products have a low degree of selectivity toward blue-green algae, are environmentally persistent, and can be perceived negatively by consumers because of the use of synthetic chemicals.

Schrader and coworkers used a bioassay to screen natural compounds for activity against O. perornata. The researchers discovered that 9,10-anthraquinone, found in some plants, was much more selective and significantly outperforms the currently used algicides in lab tests. In catfish ponds, however, efficacy testing found that anthraquinone is not very effective in killing the algae.

The researchers then tested a number of other natural quinones and discovered a proprietary compound, developed in conjunction with N. P. Dhammika Nanayakkara of the National Center for Natural Products Research at the University of Mississippi, that is very effective against O. perornata. The new algicide is currently being patented.

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