Timing Made Difference in Impact of Hard Freeze
By Linda Breazeale/MSU Ag Communications
STARKVILLE – Record low temperatures the first week of January plunged the state into a deep freeze, but the cold came too early to cause significant plant damage or have much effect on insect pests in 2014.
Lelia Kelly, horticulturist with the Mississippi State University Extension Service, said most plants were firmly in their dormant stage when the extreme temperatures hit.
“Some tender plants and evergreens like magnolias and gardenias may have some damage, but we should not overreact and remove them too quickly,” she said. “Most will shed some leaves and recover when spring and summer get here.”
Kelly said plants are challenged by cold weather when they are planted north of their target zones. Mississippi has three growth zones beginning with zone 7 in the northern counties, zone 8 in the center and zone 9 along the coast.
“Zone 7 plants can survive temperatures as low as 0 to 10 degrees. The double whammy occurs where there is wind with the cold temperatures, making the plants more susceptible to damage,” Kelly said. “Since this probably wasn’t our last cold snap, we should watch the forecasts. If you don’t want to lose plants later in the season, take steps to protect them with blankets or mulch.”
Extension fruit crops specialist Eric Stafne said while this was the best time of year for a hard freeze, some citrus is showing damage.
“We are seeing some injury to strawberry plants, satsuma, kumquat, lemon and orange trees. We don’t expect to have any damage to blueberries. They can tolerate colder temperatures than the others,” he said. “Everything should have been as dormant as it was going to be. A month later and we would have been in real trouble. Of course, we are not out of the woods yet.”
Stafne said this season has been colder than recent winters, so plants are accumulating chilling hours that will make them ready to grow when the weather warms up.
“That could impact the plants if we have late freezes. Just a week of warmer temps could cause the buds to swell, and then they will be more vulnerable if temperatures drop to the mid-20s,” he said.
Winter wheat is the only agronomic crop currently growing in Mississippi fields. As the name suggests, these wheat varieties handle low temperatures.
“We are not likely to see much damage to winter wheat at this stage of development,” said Erick Larson, Extension small grains specialist. “Early vegetative stages that have not started erect growth are more tolerant of extreme cold during the heart of winter than anytime else.”
Larson said some of the crop was younger than normal when the deep freeze hit because of fall planting delays, and lower-than-normal temperatures slowed early growth.
“Overall, cold temperatures this winter are limiting growth, but this extreme cold snap should not generally create major issues,” he said. “One of the negatives that could occur from this past hard freeze or future events is from the ground freezing and then thawing. That can pull some plants out of the ground, and the exposure would make them vulnerable and kill them.”
Larson said wheat planted with a drill is typically safe, but plants growing from broadcast seeding are more vulnerable because some seeds will not be buried deeply enough to protect the base of the plant.
Rocky Lemus, associate Extension and research professor in MSU’s Department of Plant and Soil Sciences, said annual ryegrass and clovers may have been damaged in areas where the temperature dropped below 15 degrees. In those cases, less forage would be available for livestock in the upcoming month.
“Annual clovers and small grains — especially crimson clover and bermseem clover — and oats are heavily impacted by cold damage,” Lemus said. “Some winter kill of bermudagrass, especially on fields that were lightly disked for the planting of annual ryegrass, is to be expected. Producers should allow proper resting between grazing periods and delay fertilization until new growth is observed.”
“Anytime temperatures get very cold, Mississippians start hoping it will mean fewer insect pests during the next growing season,” said Blake Layton, Extension entomologist. “Unfortunately, native pests are not affected by our winters. The best hope is that harder winters might push invasive tropical insects south, but it won’t take them long to regain their ground.”
Layton said many southern invaders, such as Argentine ants and Southern green stink bugs, tend to have greater numbers and progress further north following mild winters. He said he hopes this winter will reduce those threats.
Brian Templeton, an Extension associate in landscape architecture and a certified arborist, said most healthy trees will show little to no injuries from the freeze. Some species, such as live oaks and magnolias, may shed damaged leaves that will be replaced this spring.
“On healthy trees, woody stems are protected from the cold, and only the leaves are vulnerable, even the buds are generally protected,” he said. “Most trees have evolved to withstand these types of temperature fluctuations. However, the severe freeze could push trees that were compromised by other health conditions over the edge, resulting in losses.”
Templeton said late hard freezes are the most damaging, especially to Asian magnolias and other exotic trees, as well as some plants in the landscape that bud and flower in late winter or early spring such as camellias.
For additional information regarding plants and freezing temperatures, contact the local Extension office.