Scouting for freeze injury to bermudagrass forage

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It has been some time since winter temperatures were cold enough to cause concern for injury to bermudagrass pastures and hay fields, but this winter’s weather is in that category. Cold injury to bermudagrass is hard to predict because soil moisture and snow cover interact with temperature to increase or reduce cold injury. In general, moist soil conditions during the cold temperature period reduces cold injury and dry soil conditions during extreme cold increases potential for cold injury. The water in moist soil tends to hold heat better than dry soil. Think of it this way – dry, cold conditions tend to freeze-dry plants and roots. The longer the cold, dry weather lasts the more potential for cold injury. Snow cover insulates the soil and protects plants from extreme temperature fluctuations. Conditions are very dry statewide and as of this writing, 50 counties are under burn bans. That along with the repeated cold temperatures plunges will likely cause cold injury to some bermudagrass fields.

Assessing cold injury can’t be done in the field until the bermudagrass begins breaking dormancy. Very cold-sensitive varieties may suffer complete winterkill whereas others may exhibit slower and later greenup than normal. This will increase weed pressure and reduce season-long yield. Low soil fertility increases cold injury potential especially low soil potassium levels. The relatively mild winters in the upper south over the past several years have allowed varieties of moderate freeze tolerance to escape injury that will occur with a cyclic return to more severe winter conditions. Fewer cold-tolerant seeded varieties are available than cold-tolerant sprigged varieties. Some of the best bermudagrass varieties grown along the Gulf Coast are prone to winterkill and winter injury in Arkansas.

Some cold sensitive varieties planted from seed include Arizona Common, Jackpot, and Giant. These are commonly included in seed blends to provide quicker cover and first year yield, but tend to winterkill over time leaving the more cold-tolerant variety of the blend. Giant bermudagrass is very cold sensitive and winter kills easily. Jackpot has shown poor cold-tolerance on several farms in north Arkansas. Common survives well in the southern half of Arkansas, but may likely show winter injury this spring across north Arkansas. The most common cold-tolerant seeded variety is Wrangler. It’s cold tolerance is on par with many of the cold-tolerant hybrids grown in north Arkansas. Other commonly grown seeded varieties with moderate cold-tolerance include Cheyenne, CD-90160, and KF-194. All three have lower cold tolerance than Wrangler, but have been grown successfully in north Arkansas. The two numbered varieties are used in many seed blends sold in recent years.

When grown in colder climatic areas, varieties with moderate to low winter hardiness can be expected to begin growth later in the spring and require time to re-develop the sod density they had prior to the winter injury. This delayed spring growth makes them susceptible to weed invasion that will negatively impact their ability to reform the sod cover. Cold sensitive varieties are at greatest risk the 1st winter after seeding. Thereafter, they tend to be less susceptible to winter injury, probably because of better developed root and rhizome systems. The winter hardy Wrangler will perform better than moderately winter hardy varieties in colder climatic areas but will not perform as well when winter injury is not a factor. Research in Haskell, Oklahoma in spring of 2001 following a cold winter showed much slower greenup of Cheyenne, CD-90160, and KF-194 than for Wrangler.

The best rated sprigged bermudagrass varieties for cold-tolerance include Midland 99, Ozark, Tifton 44, and Greenfield. Newer varieties such as Vaughns #1 and World Feeder also have shown good cold tolerance. Each of those six varieties are grown in north Arkansas with little cold injury. Some sprigged varieties that are cold-sensitive include Coastal, Russell, Alicia, Jiggs, and Tifton 85. These varieties are grown only in south Arkansas. But the northern limit keeps creeping northward. Jiggs was included in trials at Booneville and commonly suffered severe winter injury. Tifton 85 is the highest yielding and highest quality variety grown in the deep south but has lower cold tolerance than Coastal. Forage specialists from Georgia, Texas, and Louisiana suggest it’s northern limit is near Shreveport, LA, but it is being grown in southern Arkansas.

Any variety with moderate or low cold tolerance, as well as those growing under fertility or other stress, should be checked closely this spring for signs of injury. Some practices that can improve recovery include proper fertility, judicious weed control, and proper grazing or hay harvest. Soil tests should be taken now to determine soil fertility levels. Fertilizer recommendations are specific for hay or pasture so be sure to note the intended use when submitting soil samples. Bermudagrass has very poor tolerance for shade so weed control is critical for winter damaged stands. Aggressive winter annual weeds or even ryegrass can form a heavy canopy in spring that delays bermudagrass greenup. The effect is much more severe on winter damaged fields. Many species of winter annual weeds are easily controlled with recommended herbicides or with properly managed grazing. Scout fields early and often to determine the best course of remediation.

Source: John Jennings – Professor, Extension Forages


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