Good weather has been helpful for harvesting forages, but has put some of our forage crops under stress and at risk.
Drought-like conditions can increase nitrate levels in a number of plants including corn, oatlage, summer annuals like sorghum or millet and even common weeds like pigweed, lambsquarters and burdock. The best way to determine nitrate levels it by testing your forage. Nitrates over 1,000 can be toxic. For forages with known high nitrate levels, waiting until drought stress has passed to harvest is best option, but in times of low forage availability you may need to harvest. Nitrates accumulate most in the stalk of the plant, so raising the cutting height can reduce risk. Ensiling these forages will reduce nitrates by half if well-packed once fermentation is complete. If you must feed these forages, dilute feed with low nitrate forages.
The low nighttime temperatures a few days ago are also a reminder of the season coming to an end. With that comes risk to our summer annual forages that could accumulate prussic acid after a killing frost. Sorghum, johnsongrass and shattercane have highest levels of this carcinogenic compound, followed by Sorghum Sudangrass cross and less so by sudangrass. If a hard frost occurs, wait seven-10 days before grazing or green chop. After a non-killing frost, regrowth can also be toxic so it is recommended not to graze or feed until the regrowth has reached a minimum of two feet in height or two weeks pass. Ensiling can reduce risk after three-four weeks of fermentation.
Many areas have experienced below average rainfall, and with that pasture regrowth has been reduced. Livestock on pastures should be closely monitored where forage availability is low as they may be more prone to eat toxic weeds in the pasture. Toxicity is often highest for many weeds under stress, at young growth stages, or in seed pods. Other toxic weeds may be less toxic this time of year.
For questions about nitrates, prussic acid and toxic weeds visit the Penn State Extension website at extension.psu.edu or call the Potter County Extension Office at 814-274-8540 extension 102.