The two conditions have, in fact, sometimes been confused. Split the nitrogen application to decrease problems. Apply phosphorous and potassium as advised by your soil test report. Stage of growth - Leaf blades normally contain higher levels of prussic acid than leaf sheaths or stems. Tillers and branches have higher levels than older plants because they are mostly leaves with little stalk material present.
Upper leaves contain more prussic acid than older leaves.
Thus, prussic acid content of sudangrass, sorghum, and sorghum-sudangrass hybrids is highest in the earlier stages of growth. As plants mature, the stalk content increases, causing the prussic acid content in the total forage to decrease only slightly with plant maturity if animals selectively graze the more tender new growth - those plant parts high in prussic acid. Sudangrass should not be grazed or green chopped until it has reached a height of at least 18 to 20 inches. Sorghum-sudangrass hybrids should not be grazed or green chopped until they have reached a height of at least 24 to 30 inches. Sorghum is generally unsafe for pasture or green chopping until after plants reach maturity.