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Vegetative stages in corn are identified by the number of collars present on the plant. The leaf collar is the light-colored collar-like “band�? located at the base of an exposed leaf blade, near the spot where the leaf blade comes in contact with the stem. Leaves within the whorl, not fully expanded and with no visible leaf collar are not included. For example, a plant with 3 collars is considered V3; however, there may be 5 to 6 leaves showing on the plant.
Understanding what is happening in the corn plant during various growth stages helps growers understand the importance of maintaining healthy, stress-free plants throughout the growing season. Some key growth stages include:
Figure 1. Corn growth stages. Adapted from University of Illinois Agronomy Handbook,1999.13;10;
Recent research on nutrient uptake and utilization in corn indicates that current corn products take up nearly 30% more N from the soil after flowering than older products (Figure 2). New research also shows that the timing of nutrient uptake in high management corn systems differs between nutrients and may have implications for nutrient management.1 Two-thirds of the total plant N and K is taken up by silking (R1). In contrast, more than one-half of the P and sulfur (S) were taken up during grain-filling stages (R2 to R5). Rremobilized from leaf and stalk tissue, N and P provide a significant portion of the grain N and P. Conversely, most of the S supplied in the grain is supplied by the soil. During the late vegetative and reproductive corn growth stages 71% of zinc and 65% of boron were also taken up by the plant. Recent fertilizer use studies indicate that nutrient removal from the soil by corn and soybean production systems may need to be adjusted to provide adequate season-long supplies of macro- and micro-nutrients.1
Figure 2. Seasonal nitrogen uptake by growth stage. Adapted from crop nutrient uptake and partitioning. 2015. University of Illinois.cropphysiology.cropsci.illinois.edu.13;10;
Corn products susceptible or moderately susceptible to diseases should be monitored prior to tasseling. Because many foliar diseases survive on corn residue and begin producing spores when wet weather favors disease development, scouting fields in a continuous corn rotation is important. It is also practical to scout fields with greater than 35 percent residue and with a history of foliar disease.2 Cool and humid weather conditions at vegetative growth stages and during grain fill can increase common rust and northern corn leaf blight in some fields. Warm and humid weather favors gray leaf spot, northern corn leaf blight, common rust, and other fungal diseases that can be managed with fungicides. These diseases can develop to levels that will reduce yields if they substantially infect the ear leaf or leaves above the ear during the weeks surrounding tasseling and pollination and thereafter.
Scouting for lesions at stages early enough to prevent severe infection of ear leaves can help establish timing for an economical fungicide treatment. The ear leaf and leaves higher on corn plants should be protected from disease because they contribute the most energy supplied during grain fill.1 A general disease treatment guideline may be to spray when disease symptoms have developed on the third leaf below the ear leaf, or on leaves above that, on half of the plants during the tasseling stage.2
Corn growth stages can also be an excellent guide for determining when to scout for insects (Table 1).
Table 1. Corn Insects by Growth Stage. Source: 2012. Corn and Soybean Field Guide. Purdue University. www.agry.purdue/dtc.