Greensnap

Greensnap, also known as brittle snap, is the condition where rapidly growing stalks are broken by strong, sudden winds associated with thunderstorm downbursts. These types of strong winds are common in Iowa, and corn is most susceptible to greensnap when it is growing rapidly. Greensnap can occur as early as the 5^th to 8^th-leaf stages (10-24 inches in height) but tends to be more common from the 12^th leaf stage through tasseling stages. New cell walls are extremely fragile and need time to harden and develop.

Several factors influence the occurrence and severity of green snap such as the timing, direction, and velocity of winds; growing conditions, management practices, and hybrid characteristics. Stalks usually snap a few nodes above or below the primary ear. Heavy wind during cool morning hours will cause more green snap than if the wind occurred during the heat of the day. Strong-rooted hybrids with less give at the base will have more greensnap than shallow-rooted plants that have a tendency for root lodging.

Conditions that favor rapid growth, like adequate nitrogen, high temperatures and good soil moisture, will increase the incidence of greensnap. Phenoxy type herbicides (2, 4-D, dicamba, and clopyralid) stimulate rapid growth and dramatically increase the chances of greensnap occurring. Greensnap is also associated with high yielding production environments.

Assessing Greensnap

Broken plants may still be able produce an ear when the greensnap occurs above the primary ear node. If the stalk is broken below the ear, it may produce a nubbin, or a small nonproductive ear, from lower ear nodes. If the stalk is only pinched, compensation may occur. A pinched stalk is crushed on one side, causing it to lean over but remain attached.

Greensnap is characterized as stalk that are broken, typically at a node. (photo credit: Licht 2012)

Corn ear development following a greensnap event. (photo credit: Saeugling 2018)

Pinched stalk between nodes on corn at the tassel (VT) stage. (photo credit: Licht 2012)

Yield Loss

Research has differed when measuring yield loss due to greensnap. Research conducted by University of Nebraska – Lincoln and University of Minnesota at Waseca concluded that yield loss decreased approximately 1% for every 1% in stalk breakage. However, Knaak’s research in Kerkhowen, MN suggests yield loss due to stalk breakage below the ear can be less severe with yield loss of 0.5% to 0.73% percent for each 1% stalk breakage. 

Summary of green snap (%) effect on corn yield (% loss) from University of Nebraska – Lincoln in 1993 and 1994; University of Minnesota in 1994 and 1995; Iowa State University from 1997 to 1999; and Knaak in 2009 and 2010.

If green snap occurs in your field, you can expect weed growth in the opened, diminished corn canopy. Weed competition for water, nutrients and sunlight will result in further yield loss. Weed growth will cause harvest difficulties and produce weed seed to be managed in future years. Stalks that are green snapped are at an increased risk for stalk and ear rots. Injured fields should receive harvest priority.

Many production practices that can lead to greensnap also are common practices to attain high yield goals. There are some factors that can be considered to minimize risk of greensnap.

• It is best not to apply growth regulator herbicides to corn past the 3^rd leaf stage.
• Hybrids differ in their vulnerability, so try planting different hybrids across a range of maturities and planting dates. You can look for greensnap ratings when selecting hybrids.
• Planting corn at least two inches deep also makes it less prone to greensnap.
• Furthermore, it can help to plant in different row orientations.  North-south rows, for example, can be protected from winds that would damage east-west rows. 
• Planting wind breaks will also protect your crop.