While bermudagrass and bahiagrass are great warm season perennials, warm season annual grasses work well in a forage system to offer high quality forage throughout the summer months. There are several warm season annuals on the market with sorghum x sudangrass and pearl millet being the most popular. In this article we will discuss grazing management for these species.
Warm season grasses can be planted in the spring as soon as soil temperatures (2 in depth) reach 65°F through July. Seed can be broadcast or drilled, ideally into well drained, fertile soils. Grazing is our most effective way to harvest warm season annuals, since they can be notorious for being difficult to dry down for making hay. Because livestock are selective in their grazing habitats, they tend to feed on the young, tender growth. Because of this, grazing should commence at the pre-boot stage. Target heights to initiate grazing varies based on species.
While continuous grazing may be the easiest way to manage livestock, it is not the best option when grazing warm season annual grasses. It is best to implement rational grazing, only turning out enough animals to effectively graze the paddock or strip for a few days. Rational grazing will allow for a rest period for regrowth, reduce waste, and prolong the stand. A down side to warm season annual grasses is the potential for high nitrate levels and prussic acid toxicity. Forages should be tested for nitrates before grazing if plant stress (such as drought or frost) has been induced, especially following N applications.
So let’s look at our most popular species:
Pearl Millet is a deep-rooted, bunch grass that is drought tolerant. Under good management, pearl millet can yield 4-6 tons per acre. Grazing can begin at 20-24 inches, but animals need to be removed at 4-6 inches to prevent plant injury and allow for regrowth. High nitrates can be an issue during drought stress especially after fertilization. Concentrations of nitrates are often highest in the stem and leaves closest to the ground. Consult with your local county extension agent about nitrate testing. A main advantage that pearl millet has over sorghum family is that it does not produce prussic acid.
Sorghum x sudangrass hybrids have the highest yield potential of warm season annual grasses if adequate rainfall or irrigation is received. Brown midrib (BMR) varieties are preferred since they have less lignin and higher digestibility. Grazing can begin at 24 inches, with animal removal at 8-12 inches. Unlike pearl millet, sorghum x sudangrass cannot be grazed as severely since the regrowth point is at the node instead of the basal bud. Nitrate toxicity and prussic acid toxicity can be an issue. Prussic acid is volatile and will dissipate in a few days. Cattle should not be allow to graze for 4-5 days after a frost. For the most part nitrate levels can be managed by limiting grazing, but a forage analysis will need to be performed to determine the level.
As stated earlier, nitrate levels can be an issue especially after fertilization, but fertilization is a must for warm season annual grasses to reach their yield potential. Fertilization and lime application should be made following soil test recommendations. Soil pH for warm season annual grasses should range from a 6.0 or higher. For grazing apply 40-60 lbs of nitrogen per acre for establishment, and 50-60 lbs per acre each month during the growing season. To help reduce the possibility of nitrate toxicity split your application of nitrogen during the growing season. When warm season annuals are damaged by drought stress, they should not receive a nitrogen application.
Pest management is important to maintain your yield and quality during the growing season. Pearl millet and members of the sorghum family are fast growing and competitive with weeds. Chinch bugs and white sugarcane aphid are common pest in warm season annual grasses. Scout your fields and apply an insecticide when economic thresholds are reached. Your county agent can help you with recommendations.
While we discussed just a few highlighted warm season annual grasses, there are other varieties and options that may fit your forage system better. Please contact your local county extension agent for more information.
