Corn Leaf Stages and Growing Degree Days (May 20, 2019)

With the fluctuation in temperatures since mid-April, corn emergence and growth has shifted week to week. At the research station, we have observed corn take up to ten days planted April 24^th, but only five when it was planted May 8^th. Rising temperatures accumulate growing degree days (GDD) in less time, so that would be expected. Looking across the region, any corn planted on May 12^th should have already emerged in Sussex, or be close to emerging in New Castle (as of May 20^th).

Table 1: Accumulated growing degree-days based on planting dates through May 20th.

Emergence = 120 GDD, V6 = 475 GDD.

Following emergence, the next important stage to manage is V6-V8, where you would typically sidedress corn. The V stage means six leaf collars, which can be identified as the white circle around the base of a corn leaf (Figure 1). Emerging, or recently emerging corn leaves will not have a collar yet. In Figure 1, counting the collars puts this field at V3. As you scout fields, some plants may be at the next stage, while the rest will catch up in a day or two.

Figure 1: Locating leaf collars on corn (left). Counting these collars will get you the corn stage (V3 in this case) to compare to GDD (right).

Statewide temperatures and rainfall since April 1^st can be seen in Figures 2 and 3. The rapid increase in temperature over the last week should have sped up emergence as well as advancing corn to the next stages. Rainfall over the weekend mostly hit the southern part of the state, increasing totals around Dagsboro and Delmar, but we have seen total rainfall of 6-9 inches since April 1^st across the state.

Figure 2: Delaware Temperatures since April 1st

Figure 3: Delaware rainfall since April 1st