Freezing Temperatures Overnight May Damage Winter Wheat at Advanced Growth Stages in KY

Figure 1. Wheat heads showing freeze
damage at heading (Feekes 10.5)

Carrie Knott, Extension Agronomist-Princeton, University of Kentucky

Last night temperatures dipped to or below 24°F for several hours at many locations throughout Kentucky (Table 1). For winter wheat that has reached the jointing (Feekes 6) growth stage, damage (Figure 1) can occur to the developing wheat head, which is above the soil surface at jointing, when temperatures are 24°F or below for at least 2 hours.

Wheat: Earlier Aphid Occurrences May Be a Consequence of the 2017’s Warm Winter

Raul Villanueva, Extension Entomologist, University of Kentucky 

Figure 1. Pictures of the bird cherry oat aphid and
 a winged English grain aphid found in wheat fields
 in February 2017. (Photo credits Yaziri Gonzales).

In Kentucky there is a complex of aphid species that feeds on wheat. The bird cherry oat, the English
grain (Fig.1), the greenbug, and the corn aphids are the most important species. Their role as vectors of plant viruses, particularly Barley Yellow Dwarf Virus (BYDV), branded them as the key pest on

wheat grain production. These aphid species overwinter as nymphs, and can be active when temperatures are above 45⁰ F. It is known that BYDV infections are more damaging when they occur in early growth stages of the wheat plant. Thus, aphids have more opportunities to infect young plants under this climatological circumstances.

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.

Kentucky Yield Contest Images are Available

Images from the Kentucky Yield Contests are available online. Feel free to download your images. University of Kentucky photographer Steve Patton took the images with professional equipment. The images are a service of the university. There are two pages of images. The first page begins with images taken during the conference. The contest winners are taken roughly in order of plaques presented during the banquet. If you don't see your images on the first page, click on the second page (bottom right corner of the screen). In case the link above does not work, you can copy and paste this address into your browser:  http://photo.ca.uky.edu/gallery/main.php/v/public/2017_Events/commodity/

The state winner images and links to all photos are also linked here.

The Kentucky Commodity Conference was held January 19, 2017 in Bowling Green, Kentucky. The awards banquet honored those who served with distinction, the top CCA for Kentucky, and the yield contest winners for wheat, soybean and corn in 2016. Lists for all the state contest winners are available at: http://www.kygrains.info/yield-contests.html

Register for the UK WHEAT PRODUCTION FIELD SCHOOL: Hands-On Training

Edwin Ritchey, Extension Soil Specialists, University of Kentucky

The UK Wheat Science Group with support from the Kentucky Small Grain Growers' Association will offer three hands-on training sessions on managing wheat in Kentucky - GREEN-UP (March 8th) - PRIOR TO FLOWERING (April 26th) - PRE-PLANT (TBA).
These trainings are directed towards crop advisors and farm managers who provide agronomic guidance for wheat production. The sessions will be held on the UKREC Farm (1205 Hopkinsville Street in Princeton, KY) from 9am - 3:00pm CST (Lunch is included). Class size is limited to 30 people per training. REGISTRATION IS REQUIRED - see links below.  

Educational credits for the March 8th “GREEN-UP training” have been approved for the following: Pesticide Credits: 3 General Hours & 1 Specific Hours (Cat 1A, 10, 12) CCA Credits: 2.5 SW, 1 PM, 2.5 CM