Corn - Making Decisions After the Freeze

        Record low temperatures occurred last Monday evening, with temperatures in the teens in some areas. It is important to check corn stands in fields that were emerged when the frost hit, as well as other fields that were about to emerge when the cold weather set in. Although the growing point on corn is below ground until it is about a foot tall (V6), some corn fields that were frosted at V2 or V3 appear to have lost some of their stand. In areas where the soils were dry and where temperatures were very cold, some growing points were killed and are now soft, mushy and brown.  Apparently the dry soils allowed the soils to freeze to the depth where the growing points were.  Tilled soils seem to have been more prone to this.  In addition, injured tissues may be susceptible to bacterial soft rot, which may injure or kill the growing points, again resulting in soft, mushy tissue at the growing points, with the tissue taking on a brownish color as the tissue dies. 

        The growing point is at the base of the shoot, about an inch or so above the seed, depending on planting depth. Some have been concerned about a mushy seed being found, but what's important is whether the growing point is firm and healthy. The plant is independent of the seed by V3 (3 leaf stage). With the warm temperatures the last few days, the regrowth should be easy to see now. It’s also important to look at the mesocotyl (between the seed and shoot) to make sure it hasn't rotted. It is less likely that the plant will survive if the mesocotyl has rotted now, which will cut off the primary (seedling) root system before the nodal root system has become established.

        It is not likely that it will pay to replant stands of 24,000 or more, if the remaining stand is fairly uniform. The uniformity of the stand and replanting costs need to be considered in making decisions on stands of less than 24,000. The following table can help in making replant decisions:

Influence of planting date and plant population on corn grain yields

Stand X 1,000	April 20 - May 5	May 13 - May 19	May 26 - June 1	June 10 - June 16	June 24 - June 28
28 – 32	100	99	90	68	52
24	94	93	85	64	49
20	81	80	73	55	42
16	74	73	67	50	38
12	68	67	61	46	35

Numerous gaps of up to 4-6 feet can reduce yields by an additional 5-6%.

For more information, see Pm-1885 "Corn Planting Guide" and NCR 344 "Uneven Emergence in Corn."