Drought-stricken plants are hazardous to feed because they are mostly leaves. Sorghum grazed or fed as green chop in the heart of a drought may retain high levels of this poison. Cold weather may kill only the tops of sorghum plants, leaving the lower portion alive. The unbound prussic acid in this forage does not decline until wilting begins. The forage is usually considered safe to pasture or feed as green chop 5-6 days after a killing frost.
New shoots emerging from unkilled portions of the plant are apt to be high in prussic acid.
Therefore, this forage should not be used until that new growth reaches a height of 2 feet. However, if high N rates are applied to soils deficient in phosphorus and potassium, prussic acid levels usually increase. Therefore, to reduce the hazard of prussic acid poisoning, maintain phosphorus and potassium levels according to soil test report recommendations. 2,4-D may cause prussic acid content to increase in forages. The effect may last several weeks.