Drought Stress On Summer Annuals

Summer annual forage species tend to be aggressive nitrate accumulators, especially in dry soil conditions. To avoid nitrate poisoning, do not apply excessive amounts of nitrogen fertilizer. Do not graze drought stressed or slow growing plants. A good forage producer should always have summer annual forages tested for nitrate levels before grazing or haying. Grazing annual forages with high nitrate levels is not generally a good idea, however, if a producer choses to graze these summer annuals under stressed environmental conditions, using strip grazing and moving the animals frequently enough that they do not consume the lower one-third of the stalk where the highest nitrate concentrations typically occur is a recommended strategy.

If nitrate levels are a problem, haying is likely the better alternative. Although the hay is still toxic in terms of nitrate levels, it can be ground and diluted into other forage stocks to minimize nitrate concentrations in livestock diets. Nitrates are stable in hay and can cause poisoning months later. When high nitrate forage is harvested as silage, nitrates can be reduced by 40-60% during the ensiling process, but there is still need to test for nitrate concentrations.

By raising the cutter bar 6 to 12 inches will minimize harvesting the higher concentrate of nitrates found in the lower part of the plant. Delay harvesting or grazing any stressed forages for 5 days after rains. The new growth will have higher amounts of prussic acid and as the plant grows after the stress, the prussic acid will be reduced.

Horses should not graze sorghum, sudangrass, and sorghum-sudangrass hybrids. These species can cause cystitis (an inflammation of the bladder), which can lead to urinary disorders, lack of coordination, and paralysis in severe cases.