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Animal Science and Forages > ASF Blog > Posts > Drought effects on Toxic Plants

As Alabama continues with below average rainfall and above average temperatures, the drought is taking its toll on the pastures and hayfields. In drought situations, animals will eat plants that they normally probably wouldn't because of the lack of forage availability. This leads to many animals eating toxic plants that are normally not eaten by them, although they have always been present in the field.  Toxic plants may be found in fields, in shade areas, or on fence lines, and although not normally palatable, animals eat them for survival. Unfortunately, toxic plants contain nitrates, cyanide, tannins, and certain alkaloids and glycoalkaolids that when eaten, can cause neurological, physiological, and even death.  

 Spiny Amaranth 2.jpg       Some common toxic plants that are present in Alabama include perilla mint, jimsonweed, pigweed, ragweed, pine trees (tannin in the needles), nightshades, groundcherry, johnsongrass, goldenrod, Canada thistle, corn, wheat, oats, sudangrass, sorghum-sudangrass, brackenfern, mountain laurel, oaks, poison hemlock, pokeweed, crotalaria, and wild cherry.  This is only a partial list of the toxic plants that are present in Alabama but are very common. 

        The age-old question of "why are my forages dying but my weeds are healthy and surviving?"  is becoming more and more prevalent as the drought continues. Weeds, unlike improved forages, have the ability to adapt to droughty conditions. They have the ability to keep water inside and maintain it, close off their stomates so that no water escapes, grow longer roots to find water, and even change their leaves so that they will keep more water. Unfortunately, improved plants that have been bred for different characteristics don't have this innate ability.  Therefore, that is why your forages are dying while your weeds are still alive.

        The question is how do I control these weeds in a drought? Since stomates must be open for a plant to "take in" a herbicide, and in a drought, stomates are closed, herbicide applications for these plants are not advised. Until there are several rains and the drought is lifted is only when a herbicide application would be advised. The only practice that is recommended is to mow selectively the toxic plants (not the forage), making sure to get all of the seed head, which is often the most toxic.  If the high temperatures continue, a frost will be delayed however, if normal temperatures start to occur, a frost can help to kill your toxic plants and aid in the control of some of them.  However, a frost can also cause nitrate levels to increase in plants, which may cause more toxicity to occur.  

 


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