Effect of Greensnap Injury on Corn Yield Potential

Greensnap mainly occurs in the Western to Central Corn-Growing Area where high winds are more prevalent. Rapidly growing corn in the late vegetative stages to tasseling is most vulnerable to greensnap. Thunderstorms, with high winds, impact the likelihood of greensnap.

Greensnap Injury

Greensnap is the breakage of corn stalks at a node caused by high winds. It is also referred to as brittle stalk or brittle snap injury. This weather related agronomic phenomenon is observed when violent thunderstorms with strong winds occur during the corn growth stage as internodes are rapidly elongating and are susceptible to breakage.

There are usually two windows of potential greensnap injury, V5 to V8 and V10 to R2. Corn hybrids with the Roundup Ready® Corn 2 gene can help reduce the incidence of greensnap, in the early window at V5 to V8, because of a reduced reliance on post-emergence applications of growth regulator herbicides. Growth regulator herbicides can significantly increase the potential risk of greensnap during the V5 to V8 window when the growing point is just emerging from the soil line.

Greensnap Injury in Corn

The corn plant is going through its most rapid rate of growth from V10 to R2. In a period of 17 to 21 days corn grows from around 4 feet to its mature height of 7 to 10 feet. During this rapid stage of growth, leaf surface area increases logarithmically. This rapid growth and increase in surface area coincides with the period of greatest potential risk of severe thunderstorms in July and early August.

Typically, greensnap injury is observed at the primary ear node or the node above or below the primary ear node. However, wind speeds above 80 mph can result in breakage at nodes above or below these typical sites.

Once a node has stopped expanding, cell walls are strengthened by the deposition of lignin that prevents breakage at that node. Straight line wind events after R1 or R2 may result in stalks kinking over or even breaking between nodes, but not actual greensnap stalk breakage which is at a node.

Yield Potential

Factors that influence the incidence and severity of greensnap in a specific field:

1. Time of day of thunderstorm and velocity of wind speed.
2. Growth stage of corn relative to the wind event.
3. Environmental conditions prior to the storm, such as soil moisture and temperature.
4. Crop management practices that influence growth and development including, tillage, fertility,    weed, and pest management.
5. Field characteristics including topography, soil type, row spacing, and row direction relative to the direction of the wind.

Assessing Storm Damage

The factors with the largest impact on greensnap damage in a particular field are the timing and severity of the wind relative to corn stage of growth. Damaging thunderstorms that occur in early morning hours typically cause the most damage during the V10 to R2 growth stage. At the base of every node is a region called a meristem, which is an area of rapidly dividing cells. Stalk growth occurs as a result of turgor pressure from water in the stalk expanding the size of these newly divided cells. Corn plants are most brittle when turgor pressure is the greatest in early morning hours when plants have taken up water overnight and are not under the heat stress of higher daytime temperatures.

Damaging winds often occur in the first minutes of a severe thunderstorm before soils are softened by rain. Hybrids with strong deep root systems in dry, firm soil may have more greensnap injury than fields with shallow root systems. Weaker root systems will tend to lodge under similar wind conditions.

Greensnap injury will typically occur at the node still undergoing rapid expansion, but has yet to be strengthened by lignin and other structural materials in the cell walls after having reached its full size. Neighboring fields may break at different levels or different nodes because hybrid maturity, planting date, or other management factors can result in different nodes being vulnerable for a specific field when wind event occurs.

The yield effects of greensnap will depend on the number of plants snapped in a field and where the breakage occurs on the stalk2. In many cases, yield loss for a greensnap event is directly related to the number of plants snapped. For example if 10 percent of the plants are broken at a lower node or near the base of the plant, a grower can expect a 10 percent yield reduction3. Depending on the timing of the greensnap event, the corn plant may have already determined maximum production of the ear and may not have the ability to compensate for reduced plant competition. Stalks that break above the ear will usually continue to grow and produce an ear; however, yield reductions may occur if nearby plants shade the broken plant2. When the stalk breaks at a node below the first ear, an ear may form at a lower node, but depending on timing and location this ear may not receive enough pollen to produce many kernels2.

Percentage Plant Breakage

In 1999, a study was conducted by Iowa State University to assess the effects of greensnap injury to corn (Table 1). The study evaluated corn yield loss resulting from three levels of simulated greensnap injury(25, 50, and 75 percent) during three different stages of corn growth (8th leaf, tasseling, and blistering (R2))4. Results from the one-year study showed that yield losses averaged over timing of breakage were 53, 32, and 15% for 75, 50, and 25% breakage, respectively, when compared to the check with no simulated breakage4.

Why are some fields impacted more than others?

Straight line winds during a severe thunderstorm are highly variable and unpredictable. This variability is easier to see when assessing damage to trees, grain bins, buildings, or telephone poles. Variability will also occur in corn fields where straight line winds can result in narrow zones of destruction with highly variable patterns in fields. A frustrating aspect of assessing wind damage is that it is often the highest yield potential fields that have the highest level of crop injury.

Managing the risk of greensnap injury

​A University of Nebraska study1 found that there was a direct correlation to higher rates of nitrogen and increased severity of greensnap damage. Crop management necessary for high yield potential contributes to rapid growth, which in turn can influence the level of wind injury.

Yield loss for pinched stalks or root-lodged plants may be more difficult to estimate, as the plant may be able to re-orientate to a vertical position and produce an ear.