– Jessica A. Williamson, Ph.D., Penn State University Extension Forage Specialist
The late spring rains and unseasonable cool temperatures have afforded our pastures exceptional growth into June in Pennsylvania, when it is common to see pasture growth begin to slow about this time of year when temperatures escalate and rainfall diminishes. However, with summer quickly approaching, it is important to remember that it is very likely that soon pasture growth will decline and the “summer slump” will be here.
Most often in the mid-Atlantic region, pastures are comprised of cool season perennial forages – including, but not limited to, orchardgrass, bromegrass, fescues, timothy, ryegrass, birdsfoot trefoil, red and white clover. Commonly, these forages thrive in the cooler temperatures and shorter days, causing grazing livestock producers to be faced with slow-growing, unproductive pastures during the hot summer months.
One of the best and easiest ways to reduce the negative effects of the summer slump is to maintain a high residue height in permanent, cool season perennial pastures during June, July, August, and into the fall. A high residue, or stubble height will allow forages to maintain their carbohydrate stores and regrow easier than with a short stubble height. Research has shown that what is above the soil is also reflected below the ground – in other words, the higher the stubble height, the deeper the roots, allowing the forages to scavenge for nutrients and water, possibly reducing the water-stress that could occur during the summer months when rainfall is often scarce. For most cool season perennial grasses, a residue height of 4” is ideal during the summer.
Planting warm season annuals for grazing can be a way to mitigate the summer slump and keep animals off permanent, established cool season perennial pastures during a time they are susceptible to drought and heat stress. Sorghum x sudangrass, sudangrass, pearl millet, and a variety of warm season legumes have been shown to grow well in the mid-Atlantic region and provide high amount of yield to sustain grazing livestock. They are best fed through strip-grazing with a back fence, so livestock cannot return to where they just grazed and forage regrowth can be allowed. For the last grazing event of the season, a back fence is not needed as forage will not regrow after that. Warm season grasses need to be monitored closely during dry weather for nitrate levels, as nitrate poisoning could occur in grazing livestock. If toxic levels of nitrate is suspected, plant tissue samples can be sent away to the Penn State diagnostic lab.
Some research has shown that overseeding warm season annuals into cool season perennial pastures can be successful with careful management. While this is a relatively new area of study and practice in the mid-Atlantic and northeast region, overseeding cool season annuals into warm season perennial pastures has been done for decades in the southern United States. “Setting back” pastures through the use of a very low rate of herbicide or overgrazing pastures down to 1” and drilling warm season annual seed into existing pastures has been the most successful way of establishment; however, this management practice is still being widely investigated and has been shown to have variable results.
A warm season perennial pasture has been shown to be successful for grazing livestock during the summer months. Switchgrass, gammagrass, and some bluestems have been proven to grow well in our region and in the vegetative stage can provide a palatable forage for grazing livestock.
Commonly, warm season forages have a lower nutritive value than cool season. Depending on the species and class of livestock that is being grazed, nutritional supplementation may be necessary to provide the livestock with an adequate quality diet to meet their dietary needs.