Pastures of tall fescue in Missouri are infected with a fungus known as the "endophyte." The tall fescue endophyte causes fescue toxicosis, a serious disorder that costs the Missouri beef industry $160 million each year and is harmful to dairy cattle, horses and sheep. Fescue toxicosis is characterized by poor health and production, including low rate of gain, poor milk production, and poor reproduction.
While many producers manage tall fescue to minimize the effects of toxicosis, other producers plan to replace their toxic tall fescue with another forage. For these producers, it is time to begin thinking of killing of the old tall fescue.
Normally, a stand of grass can be killed with a high rate of glyphosate, which is sold under a variety of different trade names but is perhaps most commonly known as Roundup. With toxic tall fescue, however, killing the stand usually requires a fairly high rate of glyphosate. That is because a single spray may not kill all the individual plants. Many plants are covered by dung piles; these plants avoid herbicide contact and often emerge later in the year. Also, a single spray does not kill the tall fescue seed present in the soil. This seed, still infected with the endophyte, can germinate and provide toxic seedlings long after the field is sprayed.
For these reasons, Missouri Extension recommends replacing toxic tall fescue with a technique known as "spray-smotherspray." There are other techniques being explored in other states, but the spray-smother-spray recipe is a proven method in Missouri. The entire procedure can be done in four months and will provide excellent summer pasture in the process. It calls for spraying glyphosate in the spring, no-tilling a smother crop in the summer, and establishing the new grass in the fall. (See Figure 1.)
The initial spray is in late May—between May 15 and May 21—which is about 1 week before a summer annual crop would be planted. Glyphosate should be applied at a rate of at least 2 lbs per acre, or 2 quarts per acre of a 4 lb/gallon glyphosate formulation. The smother crop is planted on or near June 1, and it is usually pearlmillet or a hybrid of sorghum x sudangrass. The smother crop is grazed all summer and sprayed with a second application of glyphosate in late August—between August 15 and August 21—about 1 week before the new cool-season grass is planted.
The new grass to be planted in the fall should be one that has a long growing season, is tolerant to severe climate stresses, and is nutritional to livestock. It will surely come as a surprise, but the grass that best meets these criteria is another type of tall fescue—a nontoxic one. These new varieties are infected with endophytes, but the new endophytes produce little or no toxins. In northern Missouri, the new grass is sometimes a blend of orchardgrass and endophyte-free tall fescue.
If replacing toxic tall fescue is your goal, plan ahead. And begin planning for the first step—spraying tall fescue in late May. For more information, contact your local University Extension office.
REVISED: October 5, 2015