Forage stands will begin spring greenup in the next few weeks, especially in southern Ohio. While winter injury in forages is very hard to predict, this winter has presented some very tough conditions for forage stands. This is especially true of legumes like alfalfa and red clover. Producers and crop consultants should be prepared to walk forage stands early this spring to assess their condition in time to make decisions and adjustments for the 2019 growing season.
We had some days with very cold air temperatures, but the soil temperatures have been much more moderate than you might expect. The soil temperature at the 2-inch depth is associated with the temperature of plant crowns. The coldest 2-inch soil temperatures recorded since January 1 at the Ohio State University Agricultural Research Stations occurred in late January to early February, falling to 17.8 F at Northwest, 25.4 at Ashtabula (mid-January), 30.3 F at Western, 32.3 F at Wooster, and 32.6 at Jackson. To put this in perspective, temperatures in the 5 to 15 F range as measured at or just below the soil surface can begin to damage perennial legumes and prolonged exposure to those and lower temperatures can kill the plant. Snow cover is an important component of protecting forage plants from sub-zero temperatures since even a cover of 4 inches of snow can provide 10 to 15 degrees of protection. So, it appears that the soil temperatures this winter in Ohio do not pose a concern.
The greater concern we have for injury this winter is associated with the rapid freeze/thaw cycles and saturated soil conditions. These cycles can cause plants to be physically lifted (i.e. heaved) out of the soil. The greatest potential for heaving is with taprooted legumes like alfalfa and red clover. This heaving exposes the plant crown, making it more susceptible to cold air temperatures and physical injury. In severe cases, heaving breaks off the taproot, effectively killing the plant. Heaving tends to be more of a problem in wet, saturated soils and clay soils, which are especially common in northeast Ohio.
Forage stand health evaluation and winter injury assessment needs to be done by getting out into the field once there is 3 to 4 inches of growth from the plant. This involves selecting random sites throughout the field and counting the plants in a one-foot square area. Check at least one site for every 5-10 acres, and like soil sampling, more random sampling is better.
In addition to counting the legume plants per square foot, a count of the total stems per square foot is also useful because healthy plants can often produce more stems per plant thereby compensating for potential yield loss from fewer plants per square foot. After counting the plants, dig up all the plants in a one-foot square area for every 5 to 10 acres and examine the crown and roots of the plants.
For more details on winter injury evaluation in forages, please refer to the updated Corn, Soybean, Wheat, and Forages Field Guide, available at https://extensionpubs.osu.edu/corn-soybean-wheat-and-forages-field-guide/.
Although winter temperatures and snow cover amount are primary driving factors affecting alfalfa winter survival, there are management factors that can affect the degree of winter injury suffered by forage stands. Those factors include:
- Variety selection: choose varieties with good winter hardiness and disease resistance.
- Soil fertility levels: potassium is associated with enhancing tolerance to winter injury.
- Improving soil drainage: helps prevent ice-sheeting and heaving.
- Harvest management: frequent cutting is generally associated with a higher risk of winter injury, particularly if the last fall cut falls in late September to mid-October.