Weed & Pest
Weed research Novel cheatgrass trial debuts
Douglas – In a plot north of Douglas, the Converse County Weed and Pest debuted a bacterial cheatgrass control trial on Oct. 21.
“This is the first time this bacterial control has been tried in Wyoming,” commented Converse County Weed and Pest District Supervisor Cheryl Schwartzkopf. “We are very excited.”
The trial comes after USDA Agricultural Research Service Soil Scientist and Microbiologist Ann Kennedy isolated and propagated a strain of bacteria capable of naturally inhibiting cheatgrass.
“This organism inhibits cheatgrass, medusa head and jointed goat grass,” explained Kennedy. “We have other organisms that inhibit different consortia, but this is specific to cheatgrass.”
When Schwartzkopf heard about Kennedy’s bacteria project, she jumped on the opportunity to debut the bacteria in Wyoming.
“We actually found this bacteria and this phenomenon when we looked at poor growth in winter wheat in the early spring,” noted Kennedy. “We found that a lot of the organisms clinging to the wheat were inhibitory to wheat and other grass weeds.”
Though her team started working with wheat, they soon began looking at other grasses, and the bacteria that targets cheatgrass, medusa head and jointed goat grass emerged.
The bacteria are desirable because they are not dangerous to other plants, animals or humans.
“Our goal was to find an organism that was benign in soil,” Kennedy said. “It has always been a big deal for me to see if we could find something that would survive for a little bit but not forever. It also doesn’t inhibit other plants.”
In Converse County, the bacteria were utilized in three different applications.
The bacteria are frozen, lyophilized and stored in vacuum-sealed bags after being grown in the lab.
“After we remove the oxygen, the organisms will survive for a very long time if they are kept cold,” Kennedy explained, noting that after oxygen is introduced,
The bacteria can mixed with water or herbicide and sprayed on fields, or it can be coated on seeds and planted.
“We like to spray the bacteria the best,” she said. “It is very inexpensive and easy to do.”
For about one dollar an acre, the bacteria are applied to rangelands. A plot in Converse County, north of Douglas, was treated using by mixing the bacteria with Plateau herbicide and sprayed.
“We see really good reduction and really good activity when we apply with herbicides,” Kennedy commented. “The herbicide targets the above-ground growth of the cheatgrass, and the bacteria gets the seed bank.”
Because plants that are already growing can simply grow new roots in a different location and the bacteria aren’t very motile, Kennedy explained that herbicide is necessary to eliminate emerged cheatgrass.
Additionally, the Converse County trial also utilized seed coated with the bacteria.
“When we put the bacteria on wheat seed and drill it in, it is nice and comfortable in the soil,” Kennedy explained. “On the surface, there are drying conditions, which can kill the bacteria.”
“If the organism doesn’t survive, it doesn’t work,” she added.
Rather than drilling seed, the plot north of Douglas utilized broadcast crested wheatgrass seed.
“We are using crested wheatgrass seed and rice in this trial,” noted Kennedy. “We applied the bacteria to the seed, and it will be distributed using a whirly-bird.”
To coat the seed in Douglas, the bacteria were mixed with water and distributed into gallon-sized plastic bags of seed, which were then agitated by volunteers.
“In our facility, we use a cement mixer to coat the seed,” Kennedy explained. “We try to do these projects inexpensively.”
By utilizing native plant seeds with the bacteria, Kennedy said that natives regrow as the cheatgrass is eliminated, reducing the likelihood of re-infestation of cheatgrass or other weed species.
“The real big thing is that if we just apply bacteria, we may get rid of cheatgrass,” she explained, “but either the cheatgrass comes back, or another weedy species comes in. We have to get those natives back into the rangeland system.”
In Douglas, rice was also used.
“Rice is something we have been talking about using as a potential way to aerially apply bacteria,” Kennedy said. “It is heavier than seed.”
After being distributed, the rice absorbs water and dissipates, while the bacteria works into the soil.
“Rice is not ideal because birds can eat it when it is still dry,” she said. “It gets stuck and explodes in their gullet.”
Other options include using products like spaghetti or small noodles.
She added, “The best results we’ve gotten are when the bacteria are applied every three years because it keeps enough of the organism in the system.”
The bacterial trial will occur over the next three to five years. Results are not seen until after that period because the bacteria must grow in the soil.
“The first trials we put out, people were very angry with us when they didn’t see results after the first year,” Kennedy said. “Growers came back later and said, ‘Where we put the bacteria, there is no cheatgrass.’ We realized it would take a little longer to see results.”
Since deploying trials, she noted that successful elimination of cheatgrass has resulted.
“We put out plots in the 90s on wheat, and we saw really good reductions,” said Kennedy. “We have seen a 50 percent reduction in cheatgrass – without adding any seed or using any follow-up treatments – on plots that we applied in 2009 and 2010.”
Treatments have been applied to plots across the northwest U.S., and positive results have been seen thus far.
While the final approvals are being processed by EPA and other regulatory agencies before the bacteria can be sold commercially, Kennedy noted that within the next two years, they hope to see some commercially available product.
Mechanism of inhibition
In working with bacteria to inhibit cheatgrass, Agricultural Research Service Microbiologist and Soil Scientist Ann Kennedy started to figure out that the bacteria are working in the membrane or cell walls of the plants to break down components of those cellular structure, effectively killing the cheatgrass seed.
“The bacteria disconnect certain carbons chains in the lipids of the cell wall or cellular membrane of the cheatgrass roots,” explained Kennedy. “It doesn’t allow the plant to form a good membrane, the root cells don’t grow, roots are stunted, and the activity of cheatgrass is reduced.”
Because each plant has a unique set of carbon chains within their cell walls and cell membranes, the bacteria is specific to the three target species.