Cooler May Temps and Crop Damage

Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu

Our accumulation of growing degree days (GDD) was hampered by the weekend temperatures, with very little GDD accumulated since May 6^th (Table 1). Any corn planted on April 15^th in Dover has just reached the lower threshold for emergence (Figure 1), while New Castle County’s progress was flattened by the weekend’s low temps. We may finally have broken from this abnormally cool spring and would expect the normal 7-10 days to emergence for this time of year to begin.

We are still receiving reports of damage to small grains showing up due to the freeze from mid-April, but plots around Georgetown remain unaffected. The cold temperatures this weekend has damaged emerged corn, which has been reported in both Kent and Sussex counties. The growing point of corn should remain below the surface from emergence to V4 (https://www.agry.purdue.edu/ext/corn/news/timeless/GrowingPoints.html). Any corn planted at the recommended depth should have been protected from our mild freezing temperatures. The emerged leaves may senesce and die, but the corn plant should continue to grow and make progress. We have observed some corn plants protected by standing cover crop to have less damage from any frost in Sussex County; something else to consider when choosing the first fields to plant next year (Figure 2).

Table 1. Accumulated Growing Degree Days Based on Planting Date

Figure 1. Accumulated growing degree days in each county since April 15^th

Figure 2. Fully exposed corn had more visible damage than corn planted into standing rye.