Today managing your corn crop requires knowledge of the different growth stages of the corn plant. Growth stage identification is critical for scouting and proper timing of fertilizer and pesticide applications. Throughout the growing season I will discuss the various corn growth stages and management issue at each stage.
R1 – Silking
Plants defined as Rl must have one or more silks extending outside the husk leaves. This occurs about 55 to 66 days after emergence. Silks grow about 1 to 1.5 inches per day. Plants are at maximum or near maximum height and have near maximum vegetative dry matter. Silking (Rl) is the only reproductive stage defined not on the characteristics of individual kernels. Determining the reproductive stage of the crop at and after Rl is based solely on the development of the primary ear.
The silking period is the most sensitive period for the crop; stress at this time can reduce kernel number per ear. Silks on the primary ear must be present while pollen shed occurs for successful pollination and fertilization. Synchronization between pollen shed and silking is important for obtaining high grain yields.
During Rl, both pollination and fertilization occur. Each silk is attached to one potential kernel. A pollen grain can land anywhere on an exposed silk and may germinate leading to fertilization. Silks remain receptive to pollen for a minimum of five days after they emerge. The first silks to emerge from the husk leaves are those attached to potential kernels near the base (butt) of the ear. Silks attached to potential kernels at the ear tip are last to emerge and may not be pollinated if pollen shed has ended. Some potential kernels will simply not develop into harvestable kernels due to a failure in pollination or fertilization; these kernels will be visible on the ear as small, undeveloped white mounds. As the plant approaches R2, kernels expand and have angled sides and a flatter top.
At Rl, the ear is at the beginning of a rapid elongation period and is only 40 to 45% of its final length. Potassium uptake is essentially complete and nitrogen and phosphorus uptake is rapid in the plant. Nutrient content by leaf analysis is highly related to the final grain yield at this time. A response to previously applied fertilizer can be seen.
Management/Scouting: Scout for drought symptoms, Insects: Corn Earworm, Corn Rootworm adults, and Japanese Beetles Diseases: Eyespot, Gray Leaf Spot, Norther Leaf Blight, Southern Leaf Blight and Tar Spot