Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu
Corn planted late April is at V4, which means side-dressing should be started within the next week. While the preferred timing is V6, if you believe your soil is lacking nitrogen from rainfall, or cooler soil temperatures, sidedressing at V4 could be beneficial. At our station we have observed that starter rates less than 15 lbs N per acre are obviously lacking in N.
If you are unsure of which stage you are at, one common method is to count leaves based on the presence of the collar (Figure 1a). While many leaves can be emerged from the whorl, only those with collars are considered fully developed. So, the corn plant in Figure 1a would be at V3, even though the fourth leaf is present, but still lacking the collar. As the season progresses, lower leaves are often lost. If fields are lacking in macronutrients N, P, or K, lower leaves could senesce and be lost earlier as nutrients are cannibalized and moved up to new growth (Figure 1b). If you have missed scouting some fields, you may be further ahead than you realize. One trick is to write the leaf number with a sharpie on a selected plant in the field (Figure 1c), but this will require more frequent scouting.
Figure 1: Counting corn leaves by collars (a), early loss of the first leaf (b), and writing on leaves to keep track in case leaves are lost (c).
