Area Weed Science Research
Rangelands and grasslands comprise 30 percent of land cover in the United States and are challenging environments in which to manage invasive weeds; costs are estimated at $6 billion annually. Common crupina (Crupina vulgaris) infests thousands of hectares of grasslands in Idaho, California, Washington, and Oregon degrading native and beneficial plant communities and reducing rangeland forage productivity. Dr. Matt Tancos, research plant pathologist at the ARS Foreign Disease-Weed Science Research Unit in Frederick, MD, is leading a team that is conducting research and performing regulatory reviews on the host-specific fungal pathogen Ramularia crupinae for common crupina. Field releases have been approved and ongoing studies are being conducted in the western United States. By combining the biocontrol pathogen with other tactics, rangelands will benefit from reduced populations of common crupina.
Alternative vegetable crops—such as edamame, lima bean, and snap bean—are increasingly being grown for processing, and weeds are a major production problem, but there are few cost-effective tools to manage them. Dr. Marty Williams, research ecologist at the ARS Global Change and Photosynthesis Research Unit in Urbana, IL, and his colleagues studied the role of early-terminated cereal rye cover crop on weed suppression and vegetable crop yield. The system selectively enhanced weed control in edamame and was comparable to hand weeding. A new, economically viable solution to weed management now exists that lessens the reliance on herbicides for edamame. The expanding market in the United States for alternative vegetable crops, like edamame, supports the development of a domestic industry that is both competitive and sustainable.
Understanding if weeds are reproducing primarily through clones or seedling recruitment is particularly important for sustained management with biological control (biocontrol), which relies on specialized insects with selective feeding patterns to limit weed populations. Dr. Natalie West, research ecologist at the ARS Pest Management Research Unit in Sidney, MT, led studies to survey weed density, genetic diversity, and associated biocontrol agent abundance (Aphthona species flea beetles) in 100 leafy spurge populations across North Dakota, Montana, and Idaho. The survey provided insight into 1) how frequently seedlings contribute to population growth, and thus the density of leafy spurge infestations; and 2) whether leafy spurge density is related to the abundance of biocontrol agents and the balance between clonal and seedling recruitment into local populations. No evidence was found of frequent recruitment from seed at any of the sites. Aphthona spp. flea beetles were everywhere, but the association between the number of flea beetles and leafy spurge density was not consistent. Increased importance of seed production may be changing the most effective targets for biocontrol after decades of Aphthona pressure on leafy spurge invasions. Further testing is needed to ensure biocontrol management is sufficient for long-term sustainable control.
Restoring invaded and degraded rangelands is central to recovering the health and function of these regions throughout the western United States. Federal land managers and livestock producers have found that restoration of these systems is very difficult because native plants rarely establish from seeds. Dr. Roger Sheley, research ecologist at the ARS Range and Meadow Forage and Management Research Unit in Burns, OR, is leading research on a novel restoration system that includes using buds collected from native plant crowns and stored for planned restoration efforts. Their findings suggest that buds of bluebunch wheatgrass and Sandberg’s bluegrass can be harvested mechanically and stored at about 4.4 degrees C. Bud longevity is associated with the amount of material that supports and surrounds the group of buds – the greater the amount of supporting material, the longer the stored bud remains viable. This is critically important to developing the new restoration system because crowns must be easily collectible and storable to be useful to managers.
Spliceostatin C (spC), one of the bioactive components produced by the soil bacterium Burkholderia rinojensis, has displayed high phytotoxic activity at low doses against several weeds. However, the precise mechanism of action of spC is yet to be elucidated. Dr. Joanna Bajsa-Hirschel, a research plant physiologist at the ARS Natural Products Utilization Research Unit in Oxford, MS, is leading a team in studies analyzing the genomic sequences for 13 spC susceptible and resistant weeds and has found genetic mutations that could explain the range of toxic effects of spC. These findings are providing important information for further investigation into the possibility of generating spC-resistant crops through genetic engineering and breeding and developing spC as a bioherbicide, specifically targeting herbicide-resistant weeds.