Time to kill toxic fescue, when grass grows strong

COLUMBIA, Mo. – “Now is the time to kill toxic tall fescue,” says Craig Roberts, forage specialist.

Pasture renovation to plant new novel-endophyte fescue is a long process. Mid-May is time to start spray-smother-spray controls.

In a weekly agronomy teleconference, Roberts alerted regional University of Missouri Extension agronomists across the state.

An old stand of infected fescue pasture should be sprayed to kill the toxic grass. About 10 days later a “smother crop” will be planted to continue the grass-killing recipe.

Kentucky 31 fescue is the most widely used grass on Missouri farms. However, it contains an endophyte fungus that secretes toxin. That toxin protects the plant, which makes the grass hardy. But the toxin cuts livestock gains and lowers reproduction. Those are just two of many problems.

Now there are varieties of fescue that contain new endophyte fungi that are not toxic. A new group, the Alliance for Grassland Renewal, leads efforts to replace bad grass with good grass.

The first spraying with glyphosate knocks back the pasture so that a summer cover crop can be planted. That crop will “smother” tillers that escape spraying. Also, toxic fescue seeds surviving in the soil will germinate under the cover crop.

Spraying is fairly straightforward, Roberts says. The grass must be growing vigorously to absorb the herbicide and transport it to the roots.

“Growing conditions will be ideal,” Roberts says. “There’s adequate moisture for grass growth. Temperatures will be high enough in the 70s for conditions that move glyphosate through the plant.”

The smother phase is trickier, Roberts says. He prefers to no-till drill grain crops into the dying grass. He suggests pearl millet or sorghum-Sudan grass, which are grain-growing grasses, as cover crops. The grass canopy in drill rows allows sunlight to enter the shade canopy and start growth of seedling grass and missed tillers.

A true smother crop such as crabgrass or annual ryegrass forms a thick carpet of growth that weakens remaining fescue grass. However, a thick mat of grass doesn’t allow missed tillers to grow well or let dormant toxic seed in the soil sprout and grow.

The missed fescue should be growing vigorously at the end of the summer growing season. It will then be killed by the second spraying of glyphosate.

Some producers spray twice initially to start the process. The pasture is sprayed once. A week later, missed patches or strips of toxic fescue are sprayed again. Then a cover crop is no-tilled into a clean pasture.

“The spray-smother-spray recipe works,” Roberts says. “It takes attention to details for success.”

Any toxic seedlings left alive when the new endophyte is planted will compete strongly with newly seeded novel-endophyte fescue.

The spray-smother-spray renovation was perfected at the MU Wurdack Farm, a part of the Missouri Agricultural Experiment Station, at Cook Station in the Ozarks.

Regional MU Extension agronomists can assist growers with advice on pasture replacement.