Avoid applying nitrogen to tall fescue pastures in spring

Linda Geist

COLUMBIA, MISSOURI

Livestock producers can learn how to reduce toxins that damage performance and profits during the March 23 Alliance for Grassland Renewal workshop in Mount Vernon, Missouri.

University of Missouri Extension state forage specialist Craig Roberts says ergot alkaloids in Kentucky 31 tall fescue begin to increase about mid-April in Missouri. Tall fescue is the state’s main cool-season grass.

Fescue toxins bring a host of bad side effects. In extreme cases, toxins cause fescue foot in cattle. More subtle losses are lower gains, less milk, poor calving, low weaning weight and other ills.

Adding spring nitrogen to tall fescue worsens problems inherent with ergovaline, the fungus-produced compound responsible for poor animal performance, Roberts says. “With added nitrogen comes more toxin,” he notes. “Effectively, the nitrogen aids both plant and fungus growth.”

Most tall fescue pastures grow more than most cattle can use in spring. Many forage experts, including Roberts, recommend low- to no-nitrogen fertilization during spring. Instead, save your fertilizer dollars for fall.

Fescue has two surges of growth – spring and fall. About two-thirds of the annual forage growth comes in the spring. A large application of nitrogen in spring causes grass to crowd out the legumes. If left unfertilized, legumes fix free nitrogen that is shared with nearby grass.

Producers also can reduce risks by exercising patience when turning cattle out onto spring pastures. After a long winter of feeding hay, producers might be anxious to turn cattle out onto fescue pastures. Instead, wait until fescue grows to 3-8 inches before turning cattle out, says Roberts.

And don’t let cows graze pastures too short, he says. Ergot alkaloid levels are most toxic in the bottom 2 inches of the plant.

Sometimes it pays to clip toxic tall fescue pastures before seedheads emerge, adds Roberts. “Seedheads contain high levels of the toxin. Further, waiting until after heading results in low nutritional quality. It’s a double whammy, and livestock performance will be dismal.”

Seeding novel-endophyte fescue varieties that have a nontoxic fungus simplifies nitrogen spreading decisions, Roberts says. Replacing toxic-fescue pasture proves a cure for many problems caused by grazing K-31 fescue.

Nationally recognized forage experts, including Roberts, and local producers will speak at the March 23 workshop in Mount Vernon at the MU Southwest Center.

Topics include symptoms and causes of fescue toxicosis; economics; establishment and first-year management; seed and endophyte training; transitioning from toxic fescue; products; and incentives and cost share. Find details and registration at TallFescueMo23.eventbrite.com(opens in new window).

MU Extension veterinary toxicologist Tim Evans says fescue toxicosis is one of the biggest challenges for cattle producers.

Test tall fescue pastures for endophyte infection and ergot alkaloid content during early spring, says Evans. Endophytes remain dormant through winter then break dormancy when fescue begins spring green-up.

Evans gives symptoms of ergot poisoning:

• Lameness.
• Hair loss and reddening around tops of hooves.
• Sloughing of hooves or parts of limbs.
• Losing tail switches.
• Extreme heat stress.
• Rapid breathing/panting.
• Spending more time in ponds.
• Possible staggering.
• Occasional seizures.

 “Ergotism is like fescue toxicosis on steroids,” Evans says. It is not nearly as dependent on ambient temperature. Clinical signs of hoof and tail switch sloughing during late spring and summer are generally indicative of ergot, he says.

MU’s Veterinary Medical Diagnostic Laboratory tests for ergot poisoning and other toxins. Contact Evans at evanst@missouri.edu(opens in new window) or visit vmdl.missouri.edu/toxicology(opens in new window).

For more information, see “Fescue Toxicosis/Ergot Alkaloid Exposure Updates” at https://vmdl.missouri.edu/under-the-scope-fall-2020/fescue-toxicosis-ergot-alkaloid-exposure-updates(opens in new window). ∆

Linda Geist: University of Missouri