Potential for Winter Wheat Freeze Injury

Wheat Head Freeze Damage, 2015. 
A freeze event (24°F or less for more than 2 hours)
occurred at Feekes 6 (jointing).

Carrie Knott, Extension Agronomist-Princeton, University of Kentucky

Much of Kentucky’s winter wheat crop is still tillering (Feekes 4-5; Figure 1) or just beginning to joint (Feekes 6; Figures 2 and 3). The weather forecast for this weekend is predicting that some areas of Kentucky will dip to 32°F or less. Given that most of our wheat is at Feekes 4 or 5, with some at Feekes 6, these temperatures are not cause for concern.  

Temperatures must be 12°F or less for 2 or more hours to injure wheat that is at the Feekes 4 or 5 growth stages, which much of our state is now.  For the more advanced wheat that is jointing, Feekes 6, temperatures must fall to 24°F or less for 2 or more hours.  Although the weather forecasts do not project conditions that we would expect wheat injury, examine weather data and scout your fields to determine is freeze injury occurred. 

Freeze injury can occur in small areas of fields, which are associated to low areas of fields where cold air settles.  Be sure and check for wheat stems damage close to the soil surface; characteristic symptoms of freeze damage are listed in Table 1.  It typically takes about 10 days of warm temperatures before injury can be seen.  Weather data can be accessed by clicking on the link of your county at wwwagwx.ca.uky.edu or www.kymesonet.org. 

Figure 1. Wheat field at Feekes 4 growth stage 

Figure 2. Wheat at Feekes 6 growth stage.
"Joints" are indicated with orange arrows.

Figure 3. Wheat at late Feekes 5/early Feekes 6 growth stage.
The "joint" (growing point; around the 1-3/8" mark) is right at
or slightly above the soil surface.  This 'joint' is visible
after the top few leaf sheaths were removed.   

Frost Damage and Corn Silage Options

The recent freezing temperatures essentially stopped corn growth for most of Kentucky. Farmers that had corn planted late for silage are wondering if the corn crop is still suitable for silage. The following is a brief summary, mostly from AGR-183: Late Season Frost-Damage to Corn for Silage.

Corn will ensile well at moisture levels less  than 70% for upright silos and less than 75% moisture for horizontal silos. Corn harvested at 62% to 68% moisture (late-dent stage) is ideal for ensiling.

Soybean Maturity and Fall Freeze Dates

Dr. Don Hershman released a Soybean Rust Spray Advisory for the western half of Kentucky (I-65 and west) this morning. If soybeans are at R4 (full pod) to R5 (beginning seed) then they are at risk of losing yield from soybean rust. Soybeans at R4 or R5 are also at risk to lose yield from another factor - freeze.

The median first freeze dates (32 degrees Farhenheit) for most of western Kentucky are near October 22 (about 30 days from this posting). Of course, October 22 is an average, meaning that the first freeze date can occur before or after the average. In one out of 10 years, the earliest freeze date is around October 6 (about 15 days from this posting). On the other side of the spectrum, the earliest frost freeze date can occur as late as around November 6 (about 45 days from this posting).

Generally, soybeans in Kentucky require about 30 days for seed fill (R6 growth stage). So, soybeans currently at R5 would require about 35 days to reach physiological maturity. The cool, cloudy weather might delay maturity a couple of days.

So, if you are considering spraying a fungicide to prevent yield losses from soybean rust, also consider your chances for a freeze event.

Freezing Temperatures and Wheat

Chad Lee and James Herbek, Grain Crops Extension, University of Kentucky
April 8, 2009

Freezing temperatures occured April 7, 2009 across parts of Kentucky. More freezing temperatures are expected tonight. Wheat in many fields is close to jointing, if not slightly past. Temperatures need to approach 24 degrees F or less before severe damage occurs on wheat that is jointed.

After about five to seven days of good growing conditions, we will have a much better idea of how the wheat survived. However, based on most reported night temperatures, we suspect that most of the wheat will have some leaf damage but no severe damage to yield potential.