Effects of an Early Season Frost
With temperatures dipping down to the freezing mark and lower Friday night to early Saturday, I thought it would be good to cover the potential effects of a frost on this 2020 crop. Both corn and soybeans should be able to handle a light version of a frost without too many ill effects. I consider a light frost to consist of temperatures ranging from 30-32 degrees for 1-2 hours. It is possible in this scenario for corn growth to be damaged but if the plant is small (v1-V2) it should make a full recovery due to the growing point still being below ground. Soybeans can usually handle a frost better than corn if both are emerged. A light frost could damage the first true leaves of a soybean but likely not damage the soybean cotyledons. Remember the cotyledons on a soybean plant serve as the growing point.
If temperatures stay in that 30-32 degree range for a prolonged period of time (3-4 hours or longer) or a hard freeze occurs, this is where the real threat could lie. With our ground being as wet as it is in central Illinois, I would not expect a hard freeze to affect anything that is not already emerged. However, dry soil will allow a freeze to go deeper. If you are in an area with dry soils, a prolonged hard freeze could be an issue if corn sprouts are within ½” of the surface. Soybeans in this scenario should fare much better. The soybean cotyledons and hypocotyl are much tougher and resilient than a young corn seedling. Any emerged corn during a hard freeze will likely be burnt to the ground but if the corn has not reached that v4 growth stage, I would suspect it to make a full recovery. Emerged soybeans during a hard freeze should survive if the cotyledons are not permanently damaged.
You will be able to tell if corn has been hit with a frost within the first 24 hours. Corn will turn dark green then will wilt and turn pale. Soybeans will start to show damage within the first 24-48 hours after a frost, but it will take up to five days before any real assessment of the crop can be made. If new growth in soybeans has not occurred within 7-10 days after a hard frost, then decisions will need to be made for replant. For any wheat crop, I would wait for 5 days then go split some stems and examine the seed heads for damage.
Our best friend for dealing with a frost would be for the winds to pick up and cloudy conditions to occur. If it stays clear and still, this is when a frost would likely hit. Hopefully, we can get through this weekend without too much damage and continue onward with the 2020 crop. Stay safe and stay healthy!
Illinois Sales Manager