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Area Weed Science Research


Successful invasive weeds interact with diverse resident microbes, which represent a large pool of potential biocontrol agents. The outcome of many plant-microbe interactions is context dependent, making it challenging to assess the nature of weed-microbe associations at any given timepoint but also providing opportunities to manipulate apparently benign microbes into weed-suppressive action. Genome sequences can be used to define the functional potential of microbes and prioritize them for development as biocontrol agents. Supported by an ARS AI-COE/SCINet, a graduate student is now interning at the ARS Foreign Disease-Weed Science Research Unit in Frederick, Maryland to adapt machine learning algorithms to identify genomic features associated with plant pathogenicity in bacteria. High-accuracy classification of bacterial lifestyles was achieved using the identified features, and these models were robust to the missing data common to incomplete genome sequences. The model can now be validated on newly collected microbes and will be applied to predict latent pathogenic ability in weed-associated microbes. This work is expected to increase the rate at which microbial weed biocontrol agents are found while expanding the environmental sources considered for agent discovery.


Waterhemp is a growing threat to U.S. snap bean production because it contaminates the harvested product, and few tools are available for controlling this weed. Pyroxasulfone and sulfentrazone control waterhemp before the weed emerges, but the two herbicides are not registered for use with snap bean due to concern of crop injury. Researchers at the ARS Global Change and Photosynthesis Research Unit in Urbana, Illinois, with university collaborators, determined snap bean tolerance to pyroxasulfone and sulfentrazone using a panel of 277 entries representing the diversity of snap beans grown in the U.S. over the last century. A handful of entries were tolerant to pyroxasulfone across variable environments, but the margin of crop safety is insufficient for registration of pyroxasulfone on snap bean crops. In contrast, tolerance to sulfentrazone was associated with multiple genomic regions conditioning larger seed size, oxidative stress tolerance, and herbicide metabolism. This new knowledge identifies specific genomic targets that the snap bean seed industry can use to improve sulfentrazone tolerance in sensitive lines, which may facilitate registration of the herbicide, as well as improve environmental stress tolerance in new cultivars.   


Field bindweed is a declared noxious weed or regulated species in 22 U.S. states and 5 Canadian provinces. Management includes cultivation, herbicides, and biological control, but this plant remains difficult to control in a variety of habitats and is a priority problem for organic production systems. New candidate arthropod species are being investigated for classical biological control of field bindweed, but evaluating their potential for impact requires understanding the genetic variation and reproduction strategies among North American populations. Researchers at the ARS Pest Management Research Unit in Sidney, Montana, found that different genetic lineages tended to be dominant in eastern versus western bindweed populations in North America, but variation among populations was too high to predict genetic differences based on location. Many populations reproduced by both seed and vegetative spread, but some populations reproduced entirely through rhizome expansion and without seeds. Thus, proposed biological control agents that target roots and reduce vegetative reproduction may substantially limit spread of this noxious weed, providing additional non-chemical control options to bolster integrated weed management programs for bindweed control in both traditional and organic production systems. 


The ability to restore rangeland by establishing grasses is critical but remains very difficult using only seed-based methods. New methods to improve rangeland restoration by including crown buds with seeds are necessary. It may be possible to improve seedling establishment by including growth buds from crowns of native species to augment establishment from seeds. Researchers at the ARS Range and Meadow Forage Management Research Unit in Burns, Oregon, have developed techniques for harvesting, excavating, and storing buds of native plant species, and have developed methods for successfully establishing Sandberg’s bluegrass and tufted hairgrass, two important native plants, from crown buds during restoration. This method will be useful to state and federal land management agencies, producers, conservation groups, and anyone attempting to restore these species in degraded and invaded rangeland.



Cogongrass invades many subtropical and tropical areas and is estimated to infest over 500 million hectares world-wide. Asia is most likely the native range of cogongrass from where it was accidentally first introduced to the US in packing material from Japan. Cogongrass was later intentionally introduced for forage in Texas, Mississippi, Alabama, and Florida. Cogongrass is included in the federal noxious weed list and primarily invades the Gulf Coast states from Texas to Florida, Georgia, South Carolina, and Virginia. Over 100,000 hectares are infested in Florida, Alabama, and Mississippi where cost of control may approach $400 per hectare. Cogongrass produces extensive rhizomes and seeds which allow it to spread, persist, and dominate invaded sites. The weed may reproduce vegetatively from rhizomes and is a prolific seed producer. Its leaves can grow to 1.2 to 1.5 meters in height and the plant can thrive in fire-based ecosystems. Although it was once thought to be suitable as food for cattle, the low nitrogen content, poor digestibility, and high silicate levels in the leaves deter grazing. Researchers at the ARS Invasive Plant Research Laboratory in Fort Lauderdale, Florida are conducing native range surveys for Cogongrass potential agents in Australia, Japan, and South Africa, and South Korea. The surveys revealed as many as 60 potential new agents, including a crown borer, a stem borer, a shoot tip feeder, and a shot borer. Research to colonize and host range determination is continuing.