MSU Extension

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Corn grain yield determination involves the continuous interaction of genetic, climatic, soil, plant pest, and nutrient factors present for a specific growing season. Michigan has a wide range of soil types and in most years, a high degree of variability in rainfall and pest patterns. This variability in weather and production potential makes forecasting state-wide yields a difficult proposition at best. However, from an individual farm crop management standpoint, it is helpful to characterize the most critical stages of development in the life of a corn plant with respect to determining final grain yield. The following are four critical stages in the development of a corn plant that are fundamental to determining corn grain yield and a quick assessment of how the state has progressed through each stage.

The first of these four critical corn yield determination stages is emergence. Corn does not have the ability to compensate for poor stands as well as other crops such as soybean. Establishing a uniform, optimum population stand is the first step in developing corn grain yield potential. Studies on the genetic evolution of corn indicate that modern hybrids tolerate field stress associated with higher plant populations better than their earlier genetic predecessors. Growers should continually evaluate the carrying capacity of their fields by putting in a few strip trials to determine the optimum plant population for each field. Keep in mind that as corn genetics continue to evolve, you will likely need to continually adjust your planting population upward to find that optimum plant population for each field. In general, much of the state had good to excellent conditions for corn emergence in 2008, and plant stands are correspondingly good to excellent.

The second critical growth stage is when the plant determines the number of kernel rows and the number of potential kernels (ovules) per row. This is primarily determined during the rapid phase of corn vegetative growth, which generally occurs in early to mid July in Michigan. The number of kernel rows per ear is heavily influenced by genetics and is generally determined by growth stage V12, which corresponds to the 12 leaf collar stage. The number of potential kernels per row is being determined at V12 and is usually completed a week to 10 days prior to silking (V17). The number of potential kernels per row is strongly influenced by field conditions. Managing corn to reduce environmental, pest, moisture and nutrient stress during this time will maximize the potential number of harvestable kernels. This stage, along with the pollination stage described below, determines the “sink” which the corn leaf canopy will work to fill with photosynthetically derived starch. Follow a plan to ensure adequate nutrient levels and minimize stress from pests such as weeds and insects during this critical period to establish the potential for high yield. Most areas of the state came through this second important yield determining stage of development in very good shape due to the timely rains we received throughout the early 2008 growing season.

The third critical stage is pollination. Successful pollination is required to convert potential kernel numbers to actual developing kernels. Pollination occurs when a pollen grain is shed from the tassel, lands on an emerged silk, grows down the length of the silk, and successfully fertilizes the ovule. It generally takes two to three days for all the silks on an ear to be exposed and pollinated. Pollen shed generally occurs in the late mornings and early evenings and the pollen shed period typically lasts from one to two weeks. From a management perspective, there is not a lot that can be done to ensure good pollination, since it is highly dependent upon the weather. Droughty conditions can de-synchronize pollen shed and silk emergence and also can desiccate silks and pollen grains. This results in barren ears or in short ears with barren tips. Insect pests such as adult corn rootworm beetles can feed on emerging silks and reduce pollination and therefore should be scouted during silk emergence. Finally, because the tassel and all leaves are completely exposed, the plant is especially vulnerable to hail damage at this stage. Most of the corn in the state has now completed the pollination stage of development. Consistent with the previous yield determining factors, over all, the state fared quite well during the 2008 pollination period. To assess pollination on your own farm, remove the husk from developing ears and vigorously shake. Silks on successfully pollinated kernels will drop off and silks emerging from nonpollinated ovules will stay fast.

Corn grain is sold by the pound and the final critical growth stage for determining yield is the grain fill or kernel development period. The grain fill period which begins at pollination and ends at kernel black-layer formation generally takes from 60 to 70 days (855 to 1200 GDD) for Michigan conditions depending upon climate, planting date, and hybrid relative maturity. The size and weight of harvested kernels are determined at this time and under adverse conditions kernel number can also be reduced. Ideal conditions for the grain fill period include: plenty of soil moisture; warm days; cool nights; and low humidity. Stress on the corn plant during the grain fill period can affect final yield by reducing either of these factors. Although field and machinery conditions can still influence final harvestable yield, the corn plant has physiologically completed its work once kernel black-layer has occurred.

Regarding pests, one particular insect pest to watch out for during the 2008 grain fill is the western bean cutworm (see the July 24, 2008 Field CAT Alert for more on this subject by Chris Difonzo). This pest can invade developing ears causing significant damage. Diseases to scout in the 2008 grain fill period include stalk rots. Early reports noted higher than usual anthracnose levels which could lead to isolated areas of high stalk rot incidence.

To date, the 2008 Michigan corn growing season has progressed through the first three stages of corn yield determination in very good shape, especially when contrasted with the rest of the Midwest. If adequate moisture and heat units are obtained, and insects and disease are kept in check, the stage is set for excellent 2008 state-wide yields.