Gone to the Weeds

What are your options for unwanted grasses and plants?

In many parts of the country, Weed Season (sometimes referred to as “spring”) is at hand. Lush new growth is popping up everywhere—and not just from desirable turfgrasses. How do you promote turfgrass growth and vigor (and appearance) while keeping the weeds at bay? It’s worth looking at some of the weed control options available to you.

The first line of defense against weeds should be to discourage their growth in the first place by following proper cultural practices. That means, among other things, regular mowing at a reasonable height with sharp blades; providing necessary nutrition, fertility and soil amendments; using a quality seed mix appropriate for the climate and site; supplying enough water to keep grass healthy without over-watering; scouting and treating for disease; and aerating when necessary. These types of practices will ensure that turfgrass remains healthy and strong enough to help prevent weeds (and, for that matter, disease) from invading.

It is important to follow all safety and notification procedures when applying chemical weed control treatments.

What to put down

When weeds do—and they inevitably will—show up in your turf, there are a number of chemical treatment options that can effectively control their populations. It bears reminding that with all weed control applications, be sure to follow label instructions and proper chemical application requirements and guidelines.

Here’s a brief look at just a few of the newer herbicides on the market and/or those that have recently been approved for new uses. Check with manufacturers for complete details about proper use and a complete list of weeds controlled.

• Syngenta’s (www.syngenta.com) new herbicide Tenacity (active ingredient: mesotrione) was developed when researchers attempted to synthetically mimic the allelochemicals naturally secreted by plants that kill competitive weeds. This product has both preemergent and postemergent activity and has applications in both cool and warm-season turfgrasses. Mesotrione works by inhibiting pigment in the weeds, turning them white. It controls annual weeds such as crabgrass and goosegrass, as well as perennials weeds like orchardgrass. It also has been shown to control a number of broadleaf weeds, and research also shows that it can be used as a preemergent herbicide on newly seeded areas before grass begins to grow.

• Ronstar herbicide from Bayer Environmental Science (www.backedbybayer.com) was recently approved by the EPA for use on residential landscapes to provide preemergent control of annual broadleaf and annual grassy weeds. The label revision does not include application to residential turfgrass and stipulates that Ronstar must be watered in prior to re-entry to the treated area. For weed control in turf, the company’s Revolver has been designed to control unwanted cool-season grasses like Poa annua, Poa trivialis and ryegrass that can be found in bermudagrass and zoysiagrass, as well as weeds such as goosegrass and henbit, without harming the desirable, established grasses.

• PBI Gordon Corp. (www.pbigordon.com) offers Q4 turf herbicide, which uses the protox inhibitor sulfentrazone in combination with quinclorac, 2,4-D and dicamba and is labeled for control of grassy and broadleaf weeds. It is designed to suppress yellow nutsedge, crabgrass and other broadleaf weeds quickly, typically within 24 to 48 hours. Q4 is intended for use on cool-season turfgrasses and turns weeds first pale, then reddish brown as they dry up. It provides contact as well as systemic activity.

• Certainty (sulfosulfuron) from Monsanto (www.monsanto.com) provides control of yellow nutsedge and several broadleaf weeds. It is labeled for use on several warm-season turfgrasses, including bermudagrass and zoysiagrass. It also can be used to control poa trivialis in cool-season turfgrasses. Certainty can be applied in broadcast or spot applications.

• FMC Professional Solutions (www.fmcprosolutions.com) offers its Echelon herbicide for preemergent (and early postemergent) control of a variety of annual grasses, broadleaf weeds and annual sedges, including long-lasting control of Poa annua. It is often used for control of crabgrass, and research has demonstrated quick control of goosegrass. Echelon’s active ingredients (sulfentrazone and prodiamine) work through the roots to prevent energy production, while the product also offers foliar action to inhibit photosynthesis.

Crabgrass infiltrates a lawn.

Alternative means

There are non-chemical means of controlling weeds, as well. To begin with, in areas on edges of lawns, mulch can both suffocate established weeds and prevent weeds from starting. This can, in turn, keep weeds from infiltrating into the lawn.

On turfed areas, one treatment that’s used by a number of “organic” landscape firms is corn gluten. The Northwest Coalition for Alternatives to Pesticides (www.pesticide.org) claims that corn gluten applications can be effective in controlling crabgrass, creeping bentgrass, smart weed, dandelions, redroot bigweed, purslane, lambsquarter, foxtail, barnyard grass and bermudagrass. Corn gluten works by weakening newly sprouting plants (weeds)—making them more susceptible to failure—without harming established plants (grass). There is some fertility value to these applications, as well, because corn gluten is 10 percent nitrogen.

“Corn gluten meal is typically applied to lawns with a spreader. Most corn gluten meal suppliers suggest that between 12 and 20 pounds of corn gluten meal be applied per 1,000 square feet of lawn. Typical recommendations also suggest two applications per year, the first one in the spring and a second one in the fall,” NCAP advises. There can be allergy and respiratory concerns for some applicators with this product. The U.S. EPA has granted an exemption for corn gluten meal as an herbicide, so it is not registered as a pesticide.

Other substances used to provide “natural” control of weeds include fatty acids, cinnamon bark and vinegar. These would typically be applied as spot treatments after weeds have developed. “Weed flamers” can also be used to selectively scorch weeds out of existence—these devices typically use portable propane tanks to power the burning flame, which eradicates weeds.

Perhaps the ultimate option in natural weed control is to let the turfgrass do the work for you in eliminating weed pressure. Cornell University reported last fall that researchers there had identified an herbicide naturally exuded by the roots of common fescue lawn grasses. That herbicide, it turns out, is an amino acid called meta-tyrosine, or m-tyrosine, which acts as a broad-spectrum inhibitor of weed growth in areas surrounding the turfgrass.

The ability of fescue grasses to inhibit the growth of other plants in the area had been noted by Cecile Bertin, research director for PharmAfrican, a Montreal-based bio-pharmaceuticals company. She and Frank Schroeder, assistant scientist at the Boyce Thompson Institute for Plant Research at Cornell, then conducted research that identified m-tyrosine as the source of the herbicidal affect of the grass.

“While m-tyrosine itself is too water soluble to be applied directly as a herbicide, this research may lead to development of new varieties of fescue grasses that suppress weeds more effectively, which could reduce the need for synthetic herbicides,” explained Cornell of the research findings. “By increasing our understanding of basic plant biology, the discovery of m-tyrosine’s herbicidal properties could also help researchers discover more sustainable ways to control weeds or completely new herbicide.”

Research, such as this project at Cornell, is examining the natural ability of somegrasses to suppress surrounding weed growth.

The future

There is concern among some in the industry that new weed control techniques and product solutions will need to be developed in the future, especially as the U.S. Environmental Protection Agency said recently that it will proceed with earlier announced plans to cancel registration of MSMA (monosodium methanearsonate) and other organic arsenical herbicides. EPA said that while it had “identified some risk associated with the direct use of these herbicides, the agency’s primary concern is the potential for applied organic arsenical products to transform to a more toxic inorganic form of arsenic in soil with subsequent transport to drinking water.”

This registration cancellation (technically, the EPA is actually looking for voluntary cancellation) would impact around 90 herbicide products now used by turfgrass managers and cotton growers. PLANET (www.landcarenetwork.org) has informed its members—and the EPA—that, “The benefits of MSMA are clear for licensed lawn care professionals—there is no other cost-effective herbicide available for treatment of certain weeds, including the production of turfgrass sod. Since the 1950s, the organic arsenicals have been the backbone of postemergent grass weed control in bermudagrass and zoysiagrass. However, for bermudagrass, no comparable substitute for the organic arsenical herbicides has become available. For a number of weeds, such as dallisgrass, knotgrass and vaseygrass broadleaf panicum, no control alternative exists. In addition, the organic arsenicals also control many annual and perennial sedges and a number of annual broadleaf weeds. Lack of suitable control is especially true for dallisgrass, considered the most troublesome perennial grass weed in warm-season turfgrasses. Universities have spent collectively more than 100 years in a futile attempt to find a suitable alternative.”

Despite the efforts of that national group and its members and manufacturers of control products, as of late January, the EPA had thus far been unwilling to change its course. Worse, said PLANET’s director of government affairs, Tom Delaney, the EPA has approached the issue on an expedited timetable. “Industry had proposed another mechanism for gauging the risk involved—another way of figuring it—and the EPA never responded to it. They were speeding up the process.” The industry asked for more time to prove its point and warned that if the EPA didn’t consider the science it was presenting, and allow adequate time for the subject to be studied, they wouldn’t agree to voluntary registration cancellation and that the issue could end up in court.

Delaney said in late January that he had heard from a number of members concerned about the impact MSMA’s cancellation would have on them in their sod and turfgrass businesses: “Most of the response has come from the southern states, because that’s where much of the impact would be, but there were also a number from northern states who have been complaining that they must have it for some uses.”

Delaney said in late January that he remained hopeful that some progress could be made on the issue with EPA, particularly if the industry can produce data on acceptable residue tolerances for non-food crops. “Cotton is another non-food industry that would be greatly impacted by this cancellation, so it’s possible that there might be some benefit to the green industry being ‘lumped in’ on this issue with the very powerful and important cotton industry,” he added. One goal of the industry will be to show the EPA that there is a lack of evidence of residues of arsenic in food from the use of MSMA on cotton, and that it should therefore change its approach to the issue.

Meanwhile, those in the green industry can help on the grassroots political front. “We’ve been encouraging members to contact their Congressional representatives to help push this effort along,” said Delaney. The PLANET Web site features a “legislative action center” that includes a form letter about the EPA’s approach to MSMA herbicides, making it easy to get a message directly to your representatives in the U.S. House and Senate.

Contacting your legislators now can help to ensure that next in future growing seasons you have as many weapons as possible in waging war against weeds.

Patrick White is a freelance writer and editor who is always on the lookout for interesting and unusual stories. He can be reached at pwhitevt@aol.com .