N boosts fescue but raises toxin

It is difficult to make blanket recommendations on fall nitrogen fertilizer rates to pastures because of the variability in how forages are managed in the Fescue Belt, says University of Missouri Extension State Nutrient Management Specialist John Lory.

But fescue pastures need a source of nitrogen to thrive, he says.

“Judicious use” of nitrogen fertilizer — prioritizing low fertilizer rates to stands deficient in nitrogen — will maximize yields while limiting toxicity in fescue commonly found in Missouri pastures, Lory says in an Extension news release.

Generally, limit annual nitrogen applications to 60 pounds per acre to mitigate fescue toxicity in Kentucky 31 tall fescue. It is infected with an endophyte that is harmful to animal health.

However, failure to provide a nitrogen source such as fertilizer or an interseeded legume to hayfields and pastures will rapidly reduce productivity and the quality of the stand, says Lory.

Good management begins with an understanding of how toxin levels vary during the different plant growth stages, says Lory.

Toxicity occurs in all above-ground parts of the plant, with seed heads being most toxic. Leaves peak in toxicity in spring and again in the fall. Do not overgraze toxic stands, as stems near the crown are highly toxic.

Lory recommends these strategies to limit the impact of toxic tall fescue on animal health:

• Limit nitrogen fertilizer applications on toxic tall fescue.
• Selectively graze or feed hay from toxic tall fescue. Graze when fescue is fully vegetative. Hay up to the boot stage. If seed heads have formed or are forming, consider clipping seed heads before harvesting or grazing. Do not overgraze.
• Dilute toxic fescue with other feed. Interseed legumes to reduce toxicity and to meet nitrogen needs of the fescue stand. This also dilutes the toxicity of the forage. When feeding hay, consider mixing other sources of feed to dilute the tall fescue.
• Manage excess forage. Stockpile tall fescue in the fall. Ergovaline concentrations in stockpiled tall fescue peak in September and then decrease during winter. By late winter, concentrations are low and considered nontoxic. Toxicity of tall fescue decreases by at least 30% in stored hay during the first month. However, high-moisture options such as baleage or silage preserve toxins.
• Renovate pastures by removing toxic tall fescue and planting new nontoxic novel-endophyte varieties over time.