Spring 1995 (v7n2)
A. C. Kennedy and C. M. Boerboom
USDA SARE/ACE Western Region Annual Report, p. 13. 1994
Editor's Note: In the fall 1994 issue of Sustainable Agriculture (Vol.6, No.4), we included a technical review that addressed the importance of soil microfauna (mainly nematodes and protozoa) in plant disease suppression. Although these soil animals represent a significant biological control potential, it is not clear whether or not that potential can be exploited in the field. The article reviewed here provides an example of how soil-dwelling organisms might be manipulated in cropping systems. The pest in this case is a weed; the biocontrol agents are soil bacteria.
Jointed goatgrass (Aegilops cylindrica) is fast becoming a major threat to fall-sown small grains. It now infests an estimated five million acres nationally and is reducing growers' income by $145 million annually. Herbicides for controlling this weed are not available. The objective of this research was to develop a biological weed control method that would provide an economic benefit to grain growers affected by jointed goatgrass. The approach taken was to isolate soil bacteria that could inhibit growth of the weed.
In initial greenhouse studies, four isolated bacteria reduced jointed goatgrass growth 30 to 70 percent. These isolates were used in field tests in 1993. In the field, two of the four tested bacteria effectively suppressed growth of the weed. These two isolates reduced weed emergence, but by June, visual differences in aboveground plant growth were not evident. The effect of the bacteria was more pronounced in the latter part of the growing season, because by August aboveground growth had been suppressed by 20 to 30 percent. Researchers noted that the bacteria delayed flowering and increased anthocyanin production by the weed. Wheat growth was not affected by the bacteria. In addition, the bacteria were found to be more effective when used in combination with low rates of a synthetic herbicide.
The ability of the bacteria to survive in different geographical regions, and from season to season, is critical if this biological control method is to be successful. The researchers have been able to select for isolates that are better able to withstand desiccation, but further studies under other types of stresses are needed.
For more information write to: A.C. Kennedy, USDA-ARS, Washington State University, Pullman, WA 99164-6421.
(DEC.524)
Contributed by David Chaney
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