Winter stand losses in canola: A comparison of two seasons
For the second straight year, the hardiness of winter canola has been put to the test across Kansas. Winterkill has been observed in research trials and producers’ fields from the Nebraska border to the Oklahoma border. Winterkill can depend on location, variety, and management. Fields planted a few miles from each other have shown dramatic variation in survival. Not all fields have been affected this year; fields in some parts of south central Kansas will see no impacts from winter stand losses. However, some precipitation would be helpful.
The freeze of November 2014
Winter survival is a complex trait that is influenced by many factors. We often see winterkill when a period of warm temperatures is followed by an intense decline in temperatures. That was definitely the case in 2014-2015, as the mid-November cold snap came at an inopportune time for the crop. For example, in Manhattan temperatures were very mild from September through early November, with only one hard freeze event about November 1. However, for adequate winter hardening prior to bitterly cold temperatures setting in, a few hard freezes (~26 degrees F) are beneficial to slow leaf growth, reduce cell size, and increase the concentration of soluble substances in cells making the plants more tolerant to freezing.
Figure 1 shows the low temperatures for the time period of September 1 to March 31 for the 2013-2014 and 2014-2015 growing seasons, and the 30-year average lows. A few differences can be observed. First, winter temperatures in 2013-2014 were bitterly cold for several long and frequent periods of time throughout the season. Ultimately, the duration of the cold temperatures was the most impactful factor causing winterkill.
Figure 1. Low temperatures recorded in Manhattan for the past two canola growing seasons.
Secondly, in 2014-2015, low temperatures were running about normal in the early fall, then there was a rapid decline in low temperatures in mid-November, followed by periods of above-normal low temperatures then by periods of below-normal low temperatures. The rapid decline in low temperatures quickly and severely desiccated a green, leafy crop that had not adequately winter-hardened. Additionally, low temperatures didn’t return to normal for more than a week. This and the up-and-down fluctuations in winter temperatures were the most impactful factors causing winterkill in 2014-2015. In all likelihood, if we would have experienced a normal acclimation period, the rapid decline in temperatures would not have been so devastating.
In some cases, there was complete winterkill when the crop had adequate growth going into the winter. See figures 2 and 3 as an example. This has been a rare occurrence over the past two decades. Major winter stand losses most often occur when a management factor is involved. For example: 1) late planting resulting in too little fall plant growth, 2) too much fall plant growth causing crown elevation to an unprotected position above the soil surface, 3) no-till seeding without proper residue management, and/or 4) planting a variety outside of its area of adaptation.
Figure 2. Winter canola trials at the South Central Experiment Field – Redd Foundation on October 23, 2014, with adequate growth for the winter. Photo by Mike Stamm, K-State Research and Extension.
Figure 3. Winter canola trials at the South Central Experiment Field – Redd Foundation on March 10, 2015. These trials were abandoned because of complete winterkill. Photo by Mike Stamm, K-State Research and Extension.
Fluctuating temperatures can have unseen negative consequences on crop growth and development. Sometimes freezing and thawing causes cracking in the crown or root, allowing fungi to enter that cause root decay (figure 4). Plants may appear to regrow normally in the spring, but after some time the severely damaged plants will wilt, turn bluish-gray, and eventually die (figure 5). We are starting to see this occur in a few fields. Other plants may continue to grow normally and never show any signs of damage.
Figure 4. Root decay caused by physical crown damage as a result of freezing and thawing. If severe enough, this could cause further plant loss. Photo by Mike Padgham, private crop consultant.
Figure 5. Spring stand loss caused by severe crown damage over the winter. Photo by Scott Dooley, K-State Research and Extension.
What is the impact for 2014-2015?
Canola can compensate for a thin stand because it is an indeterminate crop, producing more flower buds than it can actually support. Canola will branch out and fill in gaps in the field when stands are reduced, much like a soybean will in a reduced stand. However, moisture is critical for recovery, especially when much of the aboveground vegetation has been lost.
In 2013-2014, the canola crop in this region suffered a lack of precipitation and repeated late spring freezes at flowering and grain fill. The flowering and grain fill periods are the points of peak water demand for canola. Thus, dry spring weather in combination with winter stand thinning caused yields to be below average across much of the state. This was the case in Belleville and Hutchinson last season. See the 2014 National Winter Canola Variety Trial report of progress for Kansas locations and others across the U.S. (http://www.ksre.ksu.edu/bookstore/pubs/SRP1116.pdf)
In 2014-2015, spring conditions have been mild but we are starting to see the impact of the continued drought as the crop enters flowering. Timely rainfall and mild temperatures would go a long way toward helping the crop recovery from another challenging winter.
There are positives to this story. 1) Differential winterkill (figure 6) did occur at a few locations, meaning we have useable winter survival ratings for many of the commercial varieties we grow. 2) We now know the adaption limits of many varieties and we can make better variety recommendations for Kansas canola growers. This is important information for us to make winter canola consistent and profitable. We certainly have to be more careful in which varieties we choose, especially for canola growers north of US Hwy.50 in Kansas. Watch future Agronomy eUpdates for a summary of survival ratings and additional discussion on variety selection.
Figure 6. Differential winterkill was observed in the OSU Winter Canola Performance Trial near Pond Creek, Okla. Photo taken on March 15, 2015, by Mike Stamm, K-State Research and Extension.
Mike Stamm, Canola Breeder