Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu
For winter wheat, freeze damage is showing up from the northern half of Delaware due to the freezing temperatures from mid-April (Figure 1). Sussex temepratures stayed around 30°F in April, and some of our plots in Georgetown were flowering this week with no obvious freeze damage. Temperatures this week could cause further problems, especially in New Castle County. As many fields are heading or starting to flower, temperatures around 30°F could cause severe damage to yield (see University of Kentucky Extension: https://graincrops.ca.uky.edu/archived-topics/wheat-freeze-injury). Currently, weekend lows should stay in the mid-30s or higher in New Castle and Kent and in the upper 30s in Sussex. There isn’t much to do besides scout fields and be aware of any yield loss due to late spring temperatures.
In Sussex County, corn has begun to emerge from fields planted in mid to late April. Both fields took 13 days to emerge and pass a threshold of at least 100 growing degree days (GDD). In New Castle county, there was no difference in GDD if you planted April 15th or April 22nd and only 8 GDD difference in Sussex county (Figure 2). There has been minimal benefit in trying to plant early this April, outside of getting some fields done and spreading the workload. Temperatures this weekend may also cause some damage to emerged corn leaves, if they receive a frost, but they should recover. Lethal temperatures for emerged corn are at least 1-2 hours of below 28°F. You can read more about freeze and frost injury from Purdue Extension: https://www.agry.purdue.edu/ext/corn/news/timeless/FrostedCorn.html
Figure 1. Wheat on the left in Sussex County was flowering this week with no obvious freeze damage, while some wheat from Kent County has signs of freeze damage.
Figure 2. Accumulated growing degree days up to May 5th, if planted on April 15th or April 22nd.