Plant Concerns in Dry Weather

Clif Little, OSU Extension Educator Guernsey County

Nitrates: Plants naturally contain some nitrate, but forages and some weeds grown under stress conditions, such as drought may contain excessively high nitrate concentrations. Sudangrass, sorghum, pearlmillet,  corn, pigweeds and lambsquarter can all accumulate high levels of nitrates.  Nitrates accumulate in plants when there is a relatively large amount of available soil nitrate and plants take up the nitrates but don’t completely metabolize them into plant proteins because of poor growing conditions. High rates of nitrogen fertilization and drought are factors that contribute to nitrate buildup in plants and can harm animals when these forages are grazed, fed as green chop, or when not fermented long enough.  Nitrate accumulation tends to be highest in the lower portions of the stalks and stems of these plants.  How the forage is offered can make a difference in the likelihood of nitrate poisoning. Hungry animals fed fresh or green chop silage are more likely to consume a deadly portion.  The older and more stressed mature animals are most susceptible since their ability to transport oxygen is already compromised. In addition, rapid changes in diet, parasitism and anemic animals are more at risk.  Test any forage before it is fed if you have reason to be concerned.  Your OSU Extension office should be able to direct you to laboratories which can perform these tests.

Hydrocyanic Acid: Prussic acid, also called hydrocyanic acid, is another compound that can build to toxic levels in some plants when they are under stress from drought or frost. Sorghum, Sudangrass, Sorghum-Sudangrass, Johnsongrass, and unimproved varieties of Reed Canarygrass can all pose a threat of prussic acid poisoning. Prussic acid is not usually a concern in dry hay that is fully cured or in completely fermented silage. However, when these forages are in the boot stage of growth, have new shoots, are fed heavily with nitrogen fertilizer and grazed or fed as green chop during a drought or after a frost there is reason for concern.  When it comes to reducing the risk of prussic acid poisoning, time is our friend.  Don’t be in a hurry to graze the above mentioned drought stressed or frosted forages.  It is recommended to wait 3 weeks before feeding silage if you have reason to be concerned.  Sorghum that has wilted and dried for 6 days or more after a frost is generally considered safe. It is possible to test forages for prussic acid. Dr. Mark Sulc, OSU Forage Specialist describes the process in the Sept. 2012 issue of this newsletter,  C.L. Rhykert and K.D. Johnson of the Purdue University Agronomy Department, in “Minimizing the Prussic Acid Poisoning Hazard in Forages”, report that livestock “death on pasture are partially caused by cattle selectively grazing leaves and shoots. These plant parts may contain 2-25 times more prussic acid than stems. Cattle may also avoid frost-damaged leaves and shoots, grazing instead the young suckers lower on the plant that could contain lethal levels of prussic acid. Therefore, if new shoots develop after a frost, the crop should not be grazed until this new growth is 2 feet tall.” The treatment for prussic acid poisoning must be administered quickly and is similar to treatment for nitrate poisoning.  If you suspect any problem contact your veterinarian immediately.