2017 UK Wheat Field School - EMERGENCY FREEZE EVENT Sessions Available Online

Edwin Ritchey, Extension Soil Specialist, University of Kentucky

Photo credit: Katie Pratt, UK Agricultural Communications

Video footage from the Wheat Field School – EMERGENCY FREEZE EVENT TRAINING is now available online. The training held on Tuesday March 21, 2017 at the UKREC in Princeton was broadcast live and recorded on Zoom. Click on the links below to view recorded sessions.

UK Wheat Field School – EMERGENCY WHEAT FREEZE EVENT

Edwin Ritchey, Extension Soil Scientist, University of Kentucky

The University of Kentucky Wheat Science Group will hold a Wheat Field School – EMERGENCY

WHEAT FREEZE EVENT at the UKREC in Princeton KY. This free program consist of a series of

short information sessions as well as a hands-on training to assess wheat damage in the field. UK specialists suggest that participants attending the meeting in Princeton bring whole plant wheat samples from their farm to assess and compare to non-damaged wheat.

Topics include: Wheat Freeze Overview, Economic Considerations, Chemical Residues and Future Implications, Nitrogen Contribution to Corn if Wheat is Terminated, Livestock Feeding Potential if Grain is Not Harvested, Plant Dissection for Freeze Damage Demo, Question and Answer Session, Hands-On Wheat Freeze Assessment.

For more information please click here or call Kelsey Mehl: 270-365-7541 ext. 200 or Colette Laurent: 270-365-7541 ext 264.

Winter Wheat at Advanced Growth Stages due to Warm Winter in KY

Carrie Knott, Extension Agronomist-Princeton, University of Kentucky
Lloyd Murdock, Emeritus Extension Soil Specialist, University of Kentucky
Edwin Ritchey, Extension Soil Specialist-Princeton, University of Kentucky

Table 1. Wheat plants at jointing (Feekes 6).

Unseasonably warm temperatures in KY since wheat planting (October 15, 2016) may become a major challenge to wheat yield and profitability this year. Since Oct 15, 2016, KY has accumulated about 2000 GDD growing degree days (GDD) or heat units. In most years, only about 1500 GDD are accumulated by mid-February, while 2000 GDD are typically accumulated around the end of March in KY.

These extraordinarily warm days and large number of GDD have resulted in wheat crops that are at a more advanced growth stage for this time of year. Typically, most of KY wheat in mid-February is beginning to break dormancy and initiate active growth: Feekes 3, Green-up. However, there are several reports in KY that wheat is jointing (Feekes 6; Figures 1 & 2).

This is very concerning because at jointing (Feekes 6) the growing point (developing wheat head) is above the soil surface and is vulnerable to damage, including freeze damage. The risk of freeze damage is quite high because throughout KY there is still at least a 6 to 9 week window that a freeze typically occurs (Table 1).

Figure 2. Wheat plant at jointing with dissected wheat head. 

Table 1. Probabilities for the date of the last spring freeze (32°F) in Kentucky based upon data from 1981 to 2010 (Arguez et al., 2010 provided by S. Foster, State Climatologist for Kentucky). Probabilities that the last spring freeze will occur on or after the date listed. For example, for 90% probability the last spring freeze will occur on or later than the date listed 90% of the time (nine out of ten years), while at the 10% probability level the last spring freeze will occur on or later than the dates listed 10% of the time (one out of ten years).

Kentucky Location	Date of Last Spring Freeze (32°F or less) in Kentucky by Probability Level
	90%	50%	10%
Ashland	6-Apr	24-Apr	10-May
Bardstown	30-Mar	14-Apr	29-Apr
Bowling Green	25-Mar	9-Apr	25-Apr
Covington	2-Apr	16-Apr	2-May
Danville	27-Mar	11-Apr	27-Apr
Glasgow	29-Mar	13-Apr	27-Apr
Henderson	24-Mar	8-Apr	23-Apr
Hopkinsville	24-Mar	10-Apr	24-Apr
Leitchfield	14-Apr	28-Apr	15-May
Lexington	29-Mar	14-Apr	29-Apr
Mayfield	23-Mar	9-Apr	23-Apr
Monticello	3-Apr	20-Apr	5-May
Murray	17-Mar	2-Apr	18-Apr
Nolan River Lake	3-Apr	20-Apr	7-May
Princeton	29-Mar	13-Apr	29-Apr
Russellville	25-Mar	11-Apr	29-Apr
Shelbyville	16-Apr	29-Apr	14-May
Somerset	3-Apr	20-Apr	6-May

 

Considerations:
• For wheat crops that have not received any nitrogen, consider a single nitrogen application as late as Feekes 6 or 7 growth stage. Delaying nitrogen application may reduce plant growth and the risk of freeze damage.
    o Research in KY has shown that with sufficient tillers, nitrogen application can be delayed as late
       as Feekes 6 or 7 with little or no yield reduction.
    o Normally nitrogen is applied by Feekes 5 or 6 to maximize yield. With the accelerated growth
       this year, delaying nitrogen application until Feekes 6 or 7 could retard wheat development and
       provide additional freeze protection, depending on when a freeze occurs.
    o Yield will be reduced if nitrogen application is delayed beyond Feekes 7, such as delays due to
       weather or field conditions.
• For wheat crops at jointing, Feekes 6, that have already received nitrogen applications, there is nothing that will protect the crop from freeze damage. The best approach is to consider delaying the second nitrogen application until Feekes 6 or 7, potentially reducing the severity of freeze damage.
• Freeze injury occurs when temperatures fall to 24°F or below for 2 or more hours at the jointing growth stage: Feekes 6.
• If freezing temperatures remain above 24°F there is only a slight risk of freeze damage.
• In Western KY, the wheat crop does not appear to be as advanced as other areas of the state. Last fall there was a considerable drought that may have resulted in ‘dormant’ wheat in the fall (due to lack of water) when other areas of the state wheat was actively growing. These areas will likely be most profitable following ‘normal’ wheat management recommendations.
• Be prepared to scout fields much earlier than usual for insects and plant diseases. The warm winter temperatures have also resulted in greater insect populations in KY, specifically cereal aphid species, which may increase the incidence of barley yellow dwarf virus.

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.   

The Warm Up and Winter Wheat Status

Chad Lee, Extension Agronomist, University of Kentucky, Lexington
Carrie Knott, Extension Agronomist, University of Kentucky, Princeton
Edwin Ritchey, Extension Soil Scientis, University of Kentucky, Princeton

Wheat tillers damaged from the
freezing temperatures.
At least 7 to 10 days
of good growing conditions
are needed to assess damage.

The warming weather forecast this week will encourage many people to take a look at their wheat. We need about 7 to 10 days of good growing conditions before we will fully know the status of the wheat. That means, even though we will walk fields this week, we need to be careful about making too many decisions just yet. We can do tiller counts, we just won't know if they are viable tillers for a while.

While we won't know the status of the wheat crop for at least 10 more days, now is the normal time for the early shot of nitrogen. We can do tiller counts and make the assumption that most will survive. We can adjust the nitrogen (N) rate for total tiller count (which includes the main shoot).

Reports of Blank Heads in Wheat

Chad Lee, Jim Herbek and Don Hershman, Extension Agronomist, Extension Agronomist and Extension Plant Pathologist, University of Kentucky

There are some reports of wheat with blank heads. The plants look normal and the heads look fairly normal but there are very few of no seeds in the heads. The blank heads occur across the entire field, where for the most part, the plants look normal. Wheat in fields nearby, where heading occurred a few days earlier or later, developed properly. The most likely cause of these blank heads is freeze damage. There were a couple nights in early April when air temperatures were at or below freezing. The small, developing wheat kernel is extremely sensitive to cold temperatures. It is more sensitive than vegetative tissues (leaves and stems). The freeze events possibly caused wheat kernels at a specific stage of development to die, while wheat kernels nearby were either slightly ahead or behind, making them less sensitive to the cold temperatures. The only management at this point is to identify where this is a problem, adjust marketing commitments, and consult with your crop insurance provider.

Freeze Damage on Winter Wheat

Chad Lee and Jim Herbek, Extension Agronomists, University of Kentucky

The cold temperatures experienced yesterday in many areas and the cold temperatures expected tonight could damage the wheat crop. Wheat in the boot or heading stages generally needs temperatures at or below 30 F (-1.1 C) for at least two hours to cause severe damage. The Kentucky Mesonet reported lows of 45.1 F for Fulton County, 38.0 F for Graves County, 41.1 for Hopkins County, 42.7 F for Simpson County, and 39.6 F in Mercer County) for Sunday, May 12, 2013. None of these temperatures are low enough to severely damage wheat, but localized temperatures across fields may have been lower. 

Bleached wheat head exhibiting freeze

damage symptoms. Photo taken in 2012.

Usually, a week to ten days of warm, sunny weather is needed before the full extent of a freeze damage becomes evident. So, while we all want to scout fields today and tomorrow, a true assessment of freeze damage should not occur for about a week. Cool, cloudy days will slow wheat growth and slow the development of freeze symptoms.

Observations on the Wheat in Kentucky

Chad Lee, Extension Agronomist, University of Kentucky

Bill Bruening, our Small Grain Variety Testing coordinator, visited all of his sites on Monday and Tuesday this week. The following are his comments from around the state.

With the exception of Logan County, there was less freeze damage than I expected.  I found it difficult to make freeze damage ratings because the damaged "empty" heads were green/yellowish; but these often blended in with other healthier heads. The heads were not whitish at all, as had been expected.  During the Easter hard freeze a few years ago, heads that were emerging from the boot turned white. This 2012 crop was much further along and the freeze was not as hard.  Heads that were emerging from boot this time appear to be fine.  The damage was on those heads fully emerged from the boot.  A lot of heads also had partial damage (perhaps related to flowering location on the head at the time of freeze).  I took disease ratings there in Logan County (for Septoria  and BYDV) but there was no other disease pressure.  The barley appeared to be less damaged and looks to be three weeks from harvest.

Wheat Freeze Damage more Apparent, so are Viruses

Chad Lee, Extension Agronomist, University of Kentucky

Bleached head from freezing temperatures.
Source: Kenny Perry, Graves County ANR Extension Agent

The freeze damage on wheat became more apparent this week. The damage is spotty and tends to be more severe in the low areas of fields. Much of the wheat appears to have survived, but scouting to assess damage within fields is difficult. In order to understand the extent of damage within fields, almost the entire field needs to be walked. At the very least, the highest and lowest elevations need to be examined.

Bleached heads are a clear indication of freeze damage to heads. Girdling around the stem would be another indication of freeze. Heads that appear bent over may be a sign of damage to the stem directly beneath the head. As more days pass,  symptoms will become more visible (if damaged occurred). For more on wheat freeze damage, visit the Wheat Science Newsletter.

In central Kentucky, we are seeing a lot of Barley Yellow Dwarf Virus (BYDV) on wheat. In some cases, fields were sprayed with an insecticide. In at least one case, the field was sprayed twice. In other cases, people scouted fields, followed aphid thresholds and elected not to spray. In all cases, the warm winter most likely elevated aphid levels and climate and biology overwhelmed chemistry.

The Current Wheat Crop and Risk for Head Scab

Chad Lee, Extension Agronomist, University of Kentucky

Weather in some parts of Kentucky dipped below 30 degrees Fahrenheit last night (April 10 into this morning April 11). These temperatures are low enough to damage wheat that is heading. About 10 days of good growing conditions are needed to assess damage to the wheat crop. Some of the wheat is flowering and farmers need to make decisions now on spraying the wheat with a fungicide. Should they spray these fields?

The following is a synopsis of a conversation with Don Hershman, extension plant pathologist.