Corn at our research station is at V4, which means we will probably be sidedressing several fields next week. Anyone who planted prior to April 25th may be one leaf ahead, and plans for sidedressing should be done. 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.
Soybeans are also tracked by leaf (or node) stages, but also includes a cotyledon stage between emergence and the first trifoliate leaf stage. For soybeans VE includes initial emergence and the presence of cotyledons (Figure 2a and 2b). The VC (cotyledon) stage includes the presence of unifoliate (single leaves) above the cotyledon (Figure 2c). The V1 stage occurs when the first trifoliate (triple leaf) is fully unrolled (Figure 2d). You may continue to county unrolled trifoliate leaves until the reproductive stages begin.