Updated February 2018
Generally, about 70 percent of the annual forage production for warm-season perennial forages in southern Oklahoma and North Texas will have occurred by early July. The amount of rain between October and April contributes to the water recharge in the soil. The amount of rain in April and May often determines whether or not it's a good or poor production year. The combination of the two determines the forage production potential for the year. It takes a series of months of very favorable rainfall during the summer to overcome a significant soil moisture deficit, and that seldom occurs. Here are a couple of topics to keep in mind when anticipating a droughty growing season.
Have a drought management plan in place for your operation. The more aggressively stocked you are, the greater the probability you will actually have to use it. Drought plans have elements of de-stocking, relocating and perhaps feeding of livestock. Know and understand the economic ramifications of each alternative, as well as potential long-term effects on the forage resources. Keep in mind that introduced pasture like bermudagrass can withstand and recover from overgrazing much easier and quicker than good native pastures. It is always best to plan for and maintain an adequate amount of residual plant material, regardless of the circumstances.
Manage the use of potentially problematic forage grasses such as the toxic endophyte-infected fescue and the sorghum-sudan type grasses. These are usually good forages, but as summer progresses, they do have the potential to cause management problems for livestock.
Toxic endophyte-infected fescue is an excellent forage during the cool-season months. However, in late spring as plants develop stems and seedheads and as temperatures rise, endophyte levels are at concentrations that can cause health problems in cattle (reproductive failure, general unthriftiness, elevated body temperatures, poor blood circulation to extremities) if consumed at significant levels. It is best to remove cattle from these areas or at least have access to alternative forages where they can dilute their fescue intake. If it's necessary to utilize the fescue, you can mow pastures, removing much of the old growth, stems and seedheads, allowing cattle to graze new growth. Fescue is less of an issue if in a mixed pasture stand.
Sorghum-sudan type grasses pose different management issues. Nitrates and prussic acid can accumulate in these grasses, both of which can be deadly.. Tests can be conducted for both to determine presence and amount, but a negative test does not mean the pastures are free of nitrates or prussic acid. The Noble Research Institute can test forages for nitrates but not prussic acid. Fortunately, prussic acid dissipates from the plant tissues if cut for hay. This is not the case for nitrates.
The best means for managing nitrate accumulation is to match nitrogen fertility to moisture conditions. For example, if you fertilized Haygrazer or johnsongrass in the spring based on the moisture conditions at the time, you would have applied 50 units of nitrogen or less. In a good moisture year or under irrigation, you would be applying 70 units or more. Regardless, sample pastures prior to grazing or haying to determine levels of nitrates. Assuming that nitrates are not an issue (you have had adequate moisture and growth for the amount of nitrogen applied), but conditions are anticipated that would contribute toward prussic acid accumulations, graze cattle on the pasture prior to drought conditions and maintain their access to the fields constantly. Cattle appear to be more tolerant of prussic acid if they are in constant exposure to it as levels increase. Cattle are at the greatest risk when suddenly exposed to prussic acid that has accumulated in the plant tissues.
More information about drought management, nitrates and prussic acid, is available on the Noble Research Institute's website.