Early Cutting Recommended for Alfalfa with Rust - UNL CropWatch, Sept. 20, 2013

Early Cutting Recommended for Alfalfa with Rust - UNL CropWatch, Sept. 20, 2013

September 20, 2013

Warm, humid weather has caused rust to form in many alfalfa fields throughout our region.

Rust rarely infects alfalfa in Nebraska before mid-July because it won’t overwinter here, but if summer humidity is high, like we’ve experienced recently, rust blown up from the south can infect alfalfa.

Rust usually causes little damage in fields harvested monthly, but more mature alfalfa or alfalfa grown for seed can be injured and defoliated.

Rust cause damage in several ways:

  • Heavy rust infections can cause leaf drop and defoliation if plants aren’t cut on a timely basis. This injury will greatly reduce seed yield and quality.
     
  • Rust-infected hay sometimes causes allergic reactions in animals, more often with horses than with ruminant livestock. Rust also lowers the digestibility of hay, but this lower energy value often isn’t detected well by standard laboratory tests. If you feed rust-infected hay, your animals may not get as much energy from it as expected.

To minimize this damage growers can harvest infected fields early.

One of our biggest concerns is late summer seedings infected with rust. Infected seedlings may be weakened and not develop as much winterhardiness as normal, making them more susceptible to winterkill. If your fields have rust, monitor them closely next spring to determine early whether you need to change your cropping plans.

There’s really nothing you can do economically to control rust. So monitor, harvest, and adjust plans if needed to minimize further damage.

Bruce Anderson
Extension Forage Specialist