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As combines roll through cornfields across Nebraska, producers soon will be turning their attention to what’s next —for a lot of operations, that means getting cattle out on stalks. Corn residue grazing remains one of the most cost-effective winter feed sources available. But this year, southern rust has made a noticeable mark on fields across the state, leaving many wondering whether it changes how we manage those acres for grazing.
Southern rust (Puccinia polysora) is a fungal disease that infects corn leaves, forming small, reddish-orange pustules that often appear first on the upper leaf surface. The disease weakens plants by damaging leaf tissue, which limits photosynthesis and reduces the plant’s ability to fill grain. In severe cases, plants may die prematurely, leaving behind lighter test-weight corn and less robust stalks.
While limited research exists on the direct effect of southern rust on corn leaf nutritional quality, we do know how the disease affects plant physiology. Infection causes leaves to senesce earlier, and nutrients are remobilized from both the leaf and stalk to support grain fill when photosynthetic capacity declines. The result is a faster dry-down and often a more brittle stalk, both of which can influence the amount and condition of residue left after harvest.
So, what does this mean for grazing corn residue? Overall residue quality may be somewhat lower, but the bigger concern is that there’s simply less leaf material available. Leaves and husks are the more digestible portions of residue and make up the majority of the diet when cattle graze stalk fields. When leaf material is reduced, the quality grazing available to animals is also reduced and animals may turn to lower quality forage sources in the field. This shift can reduce overall diet quality and slow performance if stocking rates or supplementation aren’t adjusted. In addition, with earlier senescence and existing tissue damage, corn leaves are likely to decompose faster than normal. Once residue starts breaking down, grazing selectivity and overall intake drop off quickly. That means the window for quality grazing may be shorter than usual this year, particularly in fields that had moderate to severe rust infection.
The good news is that southern rust requires actively growing tissue to survive. It won’t overwinter in Nebraska crop residue or soil. Each year, spores must blow in from the south as corn begins growing. That means there’s no risk of spreading the disease through grazing or feeding residue from infected fields.
While southern rust may not drastically change residue quality directly, it can reduce the amount and availability of the higher-quality plant parts that cattle rely on. Monitoring residue condition closely and adjusting stocking rates or grazing duration can help make the most of affected fields while maintaining livestock performance.
-Ben Beckman is a beef systems Extension Educator serving northeast Nebraska. He is based out of the Cedar County Extension office in Hartington. You can reach him by phone: (402) 234-6821 or email: ben.beckman@unl.
