Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu
Corn at our research station planted early May is at V4, while corn planted in mid-April is past V6 and has already been side-dressed. 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 are nutrients are cannibalized and moved up to new growth (Figure 1b). If you have missed scouting some fields, you may be further ahead that 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).