'Blackberry Winter' damages mid-South crops
In 2007, the "Easter freeze" severely damaged crops in Central Mississippi. Large amounts of corn in the northern portion of this area were replanted as a result; however we escaped most of the effect on wheat. North Mississippi wheat was damaged so badly that some fields were not harvested, and many others produced low yields.
This year, on the evening of April 14, as a cold front moved across the South, area producers experienced flashbacks about last year's freeze; and by sunrise some of them had their fears confirmed. The early morning light of April 15 revealed a frost so white that it resembled snow, and when it melted corn plants in low-lying areas melted with it.
While damage to corn was more localized than in last year's event, some farms have damage almost equal to last year. As yet I do not have the data from the weather recording station in northwest Carroll County; however farmers reported that temperatures dropped to around 30 degrees F in that area. This caused areas of tip-burn on leaves. Strangely, around 50 miles south of Carroll County temperatures apparently descended to around 28 degrees in low-lying areas, causing complete topical damage to young corn plants. The Hill sections of both Holmes and Yazoo Counties sustained serious damage in low lying fields.
Emerged corn plants in low and flat field areas in communities like Ebenezer, Midway, Benton, Vaughan, and surrounding areas were subjected to a phenomenon called "cold air drainage," a subject most commonly mentioned in fruit and vegetable production. The early morning hours of April 15th produced perfect conditions for this: Clear skies that allowed maximum heat radiation from the ground, and almost no wind.
Since cold air is more dense than warm air, it settles to the lowest point, and in this situation the cold air was just cold enough to damage corn in lower "frost pockets," while slightly higher areas were damaged to a lesser degree or completely spared. While we can't be certain, it is likely that a difference of no more than one or two degrees separated fields with and without damage.
Corn plants are reasonably cold tolerant. The tissue of young plants does not "freeze" at 32 degrees like water. However, about 28 degrees F seems to be the magic number at which tissue damage occurs; and this is of course affected by the length of time the air is at this or lower temperatures.
Thankfully, all of the damaged corn I have checked was only damaged above the soil line. The growing points were protected by the insulating and heat radiating capabilities of the soil. These corn plants are now producing new green tissue that will allow them to resume normal growth within a few days. Little if any delay in maturity should be expected.
Quite a few low-lying corn fields will require replanting, not as a result of the freeze but of saturated and cool soil conditions prior to the freeze. We will likely replant a larger portion of this area's corn crop than in several years. In many cases, only portions of fields will be affected.