Corn is most susceptible to greensnap prior to tasseling, when it is rapidly growing. Corn plants between the 10th and 12th leaf stage (V10 to V12) are entering the "prime time" for greensnap. Plants affected by greensnap can break anywhere along the stalk. Often, plants will break at the node just below the primary ear or below the ear in the internode. Broken plants may still be able to produce a nubbin, a small nonproductive ear.
Sometimes a pinching of the stalk will occur rather than a clean break (see photo 1). Pinching is the crushing of stalk tissue on one side of the stalk causing the plant to lean over but still remain attached and intact. In fields where the soil is wet at the time of the wind storm or where rootworm feeding has occurred, root lodging tends to be more prevalent. Root lodging is where the whole stalk is leaning at an angle. Pinched and root-lodged plants will try to reorient into a vertical position and produce an ear. Yield reduction will occur from both pinched and root-lodged plants. Yield loss for damage like this is difficult to predict since it is dependent on the remaining growing conditions. Expect harvesting to be more difficult in some areas.
Photo 1: Greensnap damage at the Iowa State University Northeast Research and Demonstration Farm at Nashua, July 6, 2006. The top photo shows a plant broken at the node in the foreground and a pinched plant in the background. The bottom photo is a close view of a stalk broken at the node.
We've learned from previous greensnap events in Iowa and Nebraska that yield loss is directly related to the amount of stalk breakage that occurred. In other words, yield loss from broken plants is directly related to stand loss. If 10 percent of plants are broken this will result in a 10 percent yield reduction. This is due to a lack of compensation ability to this reduced plant competition by the corn plant this time of year. The maximum of what that ear is capable of has already been largely determined (see Number of rows and kernels set early in season)
Hybrids vary dramatically in their tolerance to greensnap. Several companies provide growers with greensnap ratings that may prove useful in selecting less susceptible hybrids. Stage of growth affects breakage too as mentioned above. Factors that increase early season growth tend to increase breakage susceptibility, such as high N, P, and K rates; spring-applied N; tillage; and high organic matter.
Plant orientation and plant populations are important factors also in understanding greensnap. With high plant densities, leaves tend to orient perpendicular to the row rather than parallel. Plants whose leaves are oriented perpendicular to the row are more likely to break than other plants when strong winds come in perpendicular to the rows. This is likely why we seldom have greensnap events (from straight-line winds) that affect both north-south and east-west rows. Plant breakage will typically occur in one row orientation or the other but not both. In the event of greensnap, producers should immediately notify their crop insurance providers of the damage and see what compensation or coverage is available to them.
We are currently conducting field and greenhouse research in an effort to better understand the physiological causes of greensnap. This research will help us to develop recommendations that may reduce greensnap in the future across the Midwest.
This article, written by Roger Elmore, Lori Abendroth, and George Cummins, originally appeared in the Integrated Crop Management extension newsletter on pages 199-200 of the IC-496(19) - July 10, 2006 issue.