Start preparing for fall weed control

Aug 20, 2010

Bright yellow. Vibrant purple. To the uneducated, yellow toadflax and purple loosestrife are just pretty flowers. When farmers, ranchers and land managers look at these plants and other noxious weeds, all they see is red. It’s not just an angry red at the expense of both time and money, but red at the bottom of a balance sheet.

Different states have different criteria for listing a plant as a noxious weed. Nebraska lists nine plants that are required by law to be controlled. South Dakota’s Department of Agriculture names seven. In addition to statewide noxious weeds, individual counties can declare a weed noxious. "We like to keep the statewide list as limited as possible, and not have too many species on that list," says Mike Moechnig, extension weed specialist with South Dakota State University. "We don’t take adding weeds to the list lightly because once they are there, control will be enforced. We prefer to spread the word and let people know that it’s a problem so they can control it voluntarily."

If a landowner doesn’t voluntarily control his noxious weeds after being notified that it is necessary, the county will do it for him or hire a contractor to do it, and the landowner will be billed. In Nebraska, if the bill is not paid within 60 days, it is added to his taxes. "Of all the notices issued to landowners, less than 10 percent require county action," says Mitch Coffin, noxious weed program manager with the Nebraska Department of Agriculture (NDA). "In most cases when a landowner receives that notice, they are more than willing to provide some treatment methods."

The cost can be one reason landowners may be hesitant to control noxious weeds, but the cost is one reason they should, says Moechnig. "All weeds that are listed as noxious have a negative economic impact, but control is also very costly. This ends up a no-win situation—landowners can’t afford to control their noxious weeds and they can’t afford not to."

Some alternatives to pricey herbicides have been used with varying success, depending on the species and situation needing control. Used carefully, sheep and goats can greatly reduce the foliage of noxious weeds. After several grazing periods, this can have a significant enough impact to reduce the population at the root level as well.

One of the major factors working to the benefit of the noxious weeds is that they usually have no natural enemies here. "All noxious weeds are non-native," Moechnig says. "The plants are introduced, often from Eurasia, but the insects and other plants that keep them in check in their natural environment are not." Some noxious weeds are introduced accidentally by seed that is mixed with a desirable seed. Other noxious weeds are introduced intentionally, as ornamentals or for another purpose, such as a windbreak or stream stabilization.

The Animal Plant Health Inspection Service has been working for years on finding and establishing enemies for some of the more prevalent noxious weeds. Before an insect is allowed to be introduced for biological control, it must undergo lengthy tests to ensure it will damage only the target plant, not desirable or native plants. Several insects have been introduced to fight leafy spurge, but a lot is still being learned about the way the plants and insects interact. Various factors can affect the effectiveness of these insects, Coffin says, including the soil type and density of stands, as well as presence of predators, such as ants.

In South Dakota, Moechnig says, he works some with the prison system in a program that allows inmates to raise the insects that have been approved for biological control of noxious weeds. "We’ve cleaned up several hundred acres of purple loosestrife with biological control agents," Moechnig says. "The number of infested acres has increased over the last five years but we’re encouraging people to be proactive and are attacking with a lot of different control methods."

In Nebraska, Coffin says, a lot of the purple loosestrife herbicide application has been done with helicopters. Since purple loosestrife spreads along waterways, accessing it for herbicide application is difficult because of the wet, boggy conditions. Nebraska has weed management areas, groups of six or eight counties that work together to control weeds, since the weeds don’t respect property boundaries. NDA has given out grants for these weed management areas to conduct the aerial spraying. The waterways can cross many landowners’ property, so it’s most effective and efficient if all the landowners are working together for the control, Coffin says. "The most important key is for everyone to cooperate on their weed control."

Many landowners take a break from weed control this time of year, but it’s time to start thinking about gearing up for a fall control program, Moechnig says. "September seems to be the most effective time to spray weeds. They’re storing food for the winter, so the herbicides get into the roots, and between the stress of the herbicide and the winter, control in the fall can be very effective." Moechnig says some plants, like Canada thistle, can be sprayed until the leaves are no longer green, which can be as late as November. However, he stresses, mid-September seems to be the most effective time to spray.

It’s also easier to identify many noxious weeds this time of year because they are in bloom, Moechnig says. Yellow toadflax, which has not been officially designated a statewide noxious weed in South Dakota, but is a species of great concern, is blooming and very conspicuous right now. The problem with this plant, Moechnig says, is that no one has found a really effective herbicide that works on it. "The only thing that has really worked is heavy applications of expensive herbicides. You start looking at $5 to $10 per acre and that’s just not affordable," Moechnig says.

Moechnig and Coffin both suggest landowners work with county weed supervisors or extension educators to set up a weed control plan. In order to do so, landowners need to identify the weeds that need to be controlled and have an idea of the extent and accessibility of the infestation. In order to determine the best herbicide, factors which must be considered include the landowner’s goals, surrounding vegetation, proximity to waterways, time of year of application, and accessibility of the area to be sprayed.

In most cases, when it is feasible, a diversified approach to control is most effective, says Coffin. "You should never rely on just one tool to get the job done." In some areas, landowners can combine intensive grazing to remove the foliage with herbicide application to kill the roots. Other times, an herbicide can be used to thin the stand of weeds enough for insects to be effective. — Maria Tussing, WLJ Correspondent