Pasture and Forage Minute: Nutrition, Disease Concerns for Crop Residue Grazing

By Ben Beckman and Todd Whitney

Southern rust has made noticeable impacts on corn fields in Nebraska this year. As these fields open for grazing following harvest, many are wondering whether rust affects how we manage livestock on those acres.

Southern rust (Puccinia polysora) is a fungal disease that creates lesions on corn leaves, weakening the plant in the process. While limited research exists on the direct effect on corn leaf quality, what we do know is that infection causes leaves to senesce earlier and nutrients to be remobilized from the leaf and stalk to help with grain fill as the plant’s photosynthetic capacity declines.

So, what does this mean for grazing residue? Overall residue quality may be somewhat lower, but the bigger concern is that there’s simply less leaf material left. Along with husks, leaves are the primary component of residue-based diets. Their loss, therefore, can indirectly lower the overall residue feed value. In addition, with earlier senescence and existing tissue damage, corn leaves are likely to decompose faster than normal — shortening the window of quality grazing even further.

There is one bright spot: southern rust requires actively growing tissue to survive, so it won’t overwinter in residue. It must blow in from the south each year, meaning there’s no risk of spreading the disease through grazing or feeding infected residue.