Image 1. Frost damage to a stand of Japanese knotweed taken 5/9/2017
Unlike Japanese Knotweed (Image 1), winter cereals are hardier and more tolerant to frost. Spring freeze injury in wheat and barley can occur but severity of damage depends on:
- the stage of the winter cereal
- length of time below 30°F
When winter cereals are still in the tillering and joint stages of development, it might surprise you the how low the temperatures can get before causing slight to moderate damage (12°F at tillering and 24°F at jointing for at least 2 hours).
Winter cereals that have headed out or are flowering, are more susceptible to freeze injury. When temperatures hit 30°F or below for at least 2 hours, damage can range from moderate to severe. To check temperatures in your area, find a weather station near you, and look up daily weather history. Weather Underground provides helpful graphs that shows the temperatures by hour, so you can determine approximately how long cereals were exposed to damaging temperatures.(Image 2)
Image 2. Daily weather history graph for Indiana, PA on May 9, 2017. Screenshot from Weather Underground.
Across Central and Western PA, much of the wheat has not headed out yet and injury is less likely. However, Barley has headed out in parts of Central PA and South West PA. Depending on the length of time that temperatures were 30°F and below, barley may have been injured.
Determining frost injury and estimating loss can be difficult, but Kansas State has a publication available that provides details on how to monitor spring freeze injury and pictures of spring freeze damage.
Image 3. Freeze injury on wheat. Picture taken by Nicole Carutis.
In the next week, monitor barley fields and growth. When freeze damage occurs after winter cereals have headed out, symptoms include: partial or complete white or yellow spike (Image 3); twisting and deformed heads (Image 4); and kernels in spikelet that have filled partially or not at all. If freeze injury and damage is severe, the winter cereal can be mowed for straw or chopped and made into silage for heifers.
Image 4. Freeze injury on wheat- a twisted, deformed spike. Picture taken by Nicole Carutis.
Freeze damage and injury to winter cereals tends to be more of a concern in southern states such as Delaware, Virginia, or Maryland than in Pennsylvania due to a warmer climate and earlier maturing winter cereals. However, if persistent freeze injury is common in your fields avoid early planting and avoid early maturing varieties.