Soil Bacteria to Control Jointed Goatgrass in Integrated Cropping Systems

Soil Bacteria to Control Jointed Goatgrass in Integrated Cropping Systems

Summary

Objectives
1. Develop the use of soil bacteria as an alternative management tool to control jointed goatgrass with emphasis on winter wheat.
2. Determine the influence of environmental stresses on the activity and survival of weed-suppressive bacteria.
3. Determine the economic impact of jointed goatgrass densities and the effect of bacterial treatments on yields of winter wheat and other rotation crops.
4. Develop a management technology that integrates weed-suppressive bacteria with cultural and chemical methods for economic control of jointed goatgrass in small grain cropping systems.
5. Transfer to growers and industry the technology of using weed-suppressive bacteria to control jointed goatgrass in small grain cropping systems.

Abstract of Results
Jointed goatgrass (Aegilops cylindrica) is fast becoming a major threat to fall-sown small grains and now infests an estimated 5 million acres in the U.S. and reduces growers net income by $145 million annually. Selective herbicides for its control are not available and the only alternatives are intensive tillage, which increases erosion, or spring cropping which reduced crop diversification and grower’s profits.

The objective of this research was to develop a novel and safe biological weed control technology that should significantly reduce costs and the need for tillage and chemical herbicides to control grass weeds in small grain crops. Six bacterial isolates were studied in depth. In greenhouse studies, weed-inhibitory bacteria reduced jointed goatgrass growth from 30 to 70 percent. In 1993 and 1994 field trials, several isolates tested were effective in reducing emergence of the jointed goatgrass. In 1993, two of the four isolates suppressed above ground growth by 20-30 percent. In 1994, three of the six isolates suppressed goatgrass above ground growth from 27 to 75 percent.

No root data was taken. We also found that different jointed goatgrass accessions, collected from various sites in the Western U.S., were more diverse in their response to the inhibitory bacteria than other weed species, which may indicate a greater genetic diversity of this weed than had originally been suggested. Greenhouse and field studies showed that the bacteria in combination with induced plant stresses such as reduced level of herbicides or root growth inhibitors were more effective in reducing plant growth than either treatment alone. We have found the bacteria to be more inhibitory when used in combination with sublethal doses of a synthetic chemical herbicide.

We followed the survival of introduced bacteria in soil an don roots. Fall introduced bacteria declined in the soil to near or below detection during the winter, but increased in the spring. The bacteria colonized roots during the fall, winter, and spring then declined with summer. Even though the bacteria in the soil declined to below detection, a sufficient population was present to colonize the root. We also investigated the use of delivery systems. When encapsulated in various formulations, bacterial survival increased 20 to 40 percent. Desiccation tolerant strains were better able to survive low moisture, thus may be better suited for field application. Using soil microorganisms to control weeds or for other agricultural purposes is a promising alternative method to reduce crop production costs, decrease dependence on pesticides, and increase the use of environmentally sound practices.

Site Information
This research was being conducted in the Pacific Northwest in the dryland agriculture region characterized by deep loessial soils, and rolling terrain. This area is predominated by winter wheat produced in a three year rotation with spring barley and cool season food legumes. Average annual precipitation ranges from 8 inches to 24 inches. Organic matter content of the soil ranges from 1 to 3 percent. The bacteria selected vary in their survival and colonization in the various soil types.

Potential Contributions
This study is helping to develop and implement a novel and safe biological seed control technology that should significantly reduce costs and the need for tillage and chemical herbicides to control grass weeds in small grain crops. The only alternatives for weed control are intensive tillage, which increases erosion, or spring cropping, which reduced crop diversification and grower’s profits. Besides lower input costs, the biological control technology should help growers reduce erosion and water pollution by enabling them to use conservation cropping systems. These types of systems are both profitable and ecologically sound while maintaining water quality.

This research has a much larger outcome than just weed control. This work will foster an extension of the new knowledge of microbioal processes such as survival in soil, specificity, secondary metabolite production, and rhizosphere colonization. This information can be used for other research purposes such as utilizing microorganisms as a mechanism for delivery of any desired compound to the root surface. It can also help scientists to understand how the soil microbial component can be managed to reverse soil degradation and aid in maintaining a healthy and productive soil.

Farmer Adoption
This technology requires a paradigm shift on the user group because weed control is occurring without the sole use of a synthetic chemical. In this biocontrol system, synthetic chemicals are replaced or used at a reduced rate in conjunction with the biocontrol agent. Until now it was considered necessary to have near 100 percent control of the weed. When one considers the impact microorganisms can have on the competitive abilities of a plant by just suppressing plant growth, which involves consideration of the ecology of both the weed and the bacteria for successful weed control. This plant-microbe interaction along with the weed-crop interaction will effectively reduce the weed pressure and attain the true yield potential.

Reported in 1996.