Small Grain Freeze Damage and Current Growing Degree Days

Jarrod O. Miller, Extension Agronomist,

The generally accepted starting date for corn planting in Delaware is April 15th, after which our chances of a freeze are supposed to be low. This was not the case this year, as Newark had a low of 28°F while Georgetown only dropped to 30°F on April 17th. This small difference can be important. We have still not observed much damage to wheat and barley fields in Georgetown, while fields in the northern end of the state may eventually have bleached, dead kernels due to the 28°F temperatures. We have not been able to observe any fields north of Georgetown to determine their conditions.

It is also recommended to plant corn when temperatures are greater than 50°F, which has been the case over the past two weeks. However, the temperature has barely risen above 50°F, slowing the accumulation of growing degree days (GDD) and limiting germination. Anyone who planted on April 15th has only accumulated 2.3 (New Castle), 10.8 (Kent), or 25.1 (Sussex) GDD over a two-week period. Corn emergence requires about 120 GDD to emerge, so not even Sussex County should be that close. To match the April 2019 emergence timing of 10 days, we would need 12 GDD per day, which no part of the state is observing. If you have waited to plant your fields, it was probably a good idea. Warmer temperatures are in the forecast, and planting at this time would probably see us reaching the 7-10 day emergence window, particularly in Sussex County. Corn planted last week has germinated, and we do expect it to emerge soon. If you have observed fields emerge over the last two weeks, let me know, so we better understand how emergence may occur in cooler springs.

Growing degree days accumulated across Delaware since April 15th

Figure 1. Growing degree days accumulated across Delaware since April 15th.