As temperatures fall, what factors influence the survival of winter canola?
There was a narrow window for planting winter canola in September 2019. For those in northern parts of the growing area, early September rains set the stage for favorable conditions for stand establishment. Others in central and southern Kansas weren’t as lucky as producers waited on a rain to plant the crop. September began with dry conditions and ended with heavy rains. This delayed planting even further as producers waited for dry field conditions, and some were delayed to the point where they couldn’t get the crop in on time. In southwest Kansas, dryland establishment of canola would have been complicated, if not compromised, by dry soils. Soil moisture aids rapid and timely emergence of canola, which is critical in attaining the right amount of top and below-ground growth heading into the winter months. How could this, and other factors, affect the winter survival of canola?
Effect of canola plant size on winter survival
Canola overwinters -- and is the most tolerant to cold temperatures -- in the rosette growth stage. At this stage, the crown develops at the soil surface with larger, older leaves at the base and smaller, newer leaves at the center. The stem thickens but its length remains unchanged. To have the best chance at survival, a winter canola plant needs 5 to 8 true leaves, 6 to 18 inches of fall growth, a root collar diameter of ¼ to ½ inch, and an extensive root system. Adequately hardened winter canola can withstand temperatures below 0 degrees F for short periods of time.
On the other hand, canola that has too much top growth (typically 24 inches or more) can succumb to winterkill for a number of reasons, including overuse of available soil water and nutrients, stem elongation above the soil surface, and physical damage to the unprotected crown as winter temperatures arrive.
Causes of excessive fall stem elongation
Stem elongation in the fall -- not to be confused with bolting, i.e. stem elongation with visible flowering structures -- may occur because:
- The crop was planted too early allowing growth to continue longer than necessary.
- The crop was seeded at higher-than-optimal plant populations, leading to competition for light resources. This causes etiolation, or an overextension of the plant hypocotyl (the part of the stem between the roots and the cotyledons).
- Excessive soil fertility is present (particularly nitrogen) causing an overabundance of top growth.
- An unusually warm fall persists with no hard freeze events to slow the crop down
- Selection of a poorly adapted cultivar that is more prone to fall stem elongation
- A combination of any of these factors
To explain, closely spaced and crowded canola plants increase early plant-to-plant competition for light. This “reaching” for light may lead to an extension of the growing point above the soil surface. Any time the growing point (rosette) is elevated, the chances for winterkill are increased because overwintering plant parts are in an unprotected position above the soil surface.
Another factor in stem elongation and winter survival is the amount of surface residue present in the seed row, especially in no-till cropping systems. Too much residue in the seed row can have a buffering (lowering) effect on the temperature surrounding canola plants. This temperature lowering can have a negative impact on survival. In addition, K-State research has shown that residue removal from the seed row is important for keeping the rosette close to the soil surface and more protected. Appropriate residue management (any method to remove residue from the seed row) greatly benefits winter survival.
Planting dates in 2019
As mentioned above, soil moisture conditions dictated planting dates for winter canola in 2019. Late September rains, although needed, delayed planting (Figure 1) in southern Kansas as soils did not dry out in a timely manner. Starting out too dry and ending too wet was a significant challenge in southern Kansas. Fortunately, planting dates can be delayed into October in Barber, Harper, and Sumner counties, and the crop should be able to overwinter if warmer than normal conditions persist in November.
Figure 1. Winter canola plots were seeded into a stale seedbed with highly favorable moisture conditions near Caldwell, KS on October 15, 2019. This is about 10 days beyond the optimum for planting canola in this part of the state (Photo by Mike Stamm, K-State Research and Extension).
Where canola was seeded on time near Manhattan and Belleville, we are seeing adequate fall growth and there should be little initial concern for this crop going into the winter (Figure 2). At the South Central Experiment Field near Hutchinson, trials were planted on September 20 and a rain was needed for emergence to happen (Figure 3). There is some concern that the current late-October cold snap could negatively affect survival of the crop. Because of the delayed emergence (2 to 3 weeks post planting), the plants do not possess adequate size for overwintering at this time. If temperatures rebound to the 40s and 50s for highs with lows near freezing for a few weeks, this crop should continue to add leaf area before repeated hard freezes move it into dormancy. Warmer temperatures would greatly benefit any late-planted canola.
For those producers concerned about cold temperature effects, visit canola fields about five days after the hardest freeze event. Look for bleached (whitened) leaves, wilted plants, and dead plants (dry and brown) where temperatures dropped below 30 degrees F for several hours. Plant loss will be the biggest concern on canola with 2 or fewer true leaves. Canola that emerged late because of too much or too little soil moisture will be at the greatest risk for cold temperature losses.
Figure 2. Canola plots near Manhattan, KS on October 11, 2019. These plants have four true leaves and are continuing to add leaf area (Photo by Scott Dooley, K-State Research and Extension).
Figure 3. Winter canola stands at the South Central Experiment Field, Hutchinson, planted on September 20. These plants are smaller-than-normal for October 18. Emergence was delayed until rain fell in early October (Photo by Scott Dooley, K-State Research and Extension).
Will the fields with small canola succumb to winterkill?
It is hard to answer this question because there are a number of factors that can affect winter survival. Good winter survival begins with selecting a winter hardy cultivar. Management of the crop, including planting date, fertilization, and seeding rate, can affect overwintering. The environment has the biggest influence and individual canola fields may see different effects from the cold. The ultimate low temperature and the duration of below-freezing temperatures are things to keep in mind when weighing what might happen. In addition, better survival is often seen when temperatures gradually drop versus rapidly drop. Soil moisture can also influence survival when canola is small, as cold and wet conditions often promote better survival than cold and dry conditions. In the end, an interaction of all these factors will determine how the crop will overwinter. November is typically when canola begins to acclimate to winter conditions. Low temperatures at or below 30 degrees F repeated over several days are essential for winter hardening.
Cultivar differences in overwintering potential
Cultivar differences exist for fall vigor, the ability to avoid fall stem elongation, and winter survival, so it is important to consider these traits when considering what cultivar to grow. Certain open-pollinated and hybrid cultivars have quick establishment in the fall. This is an important trait because it results in rapid plant development, both above and below ground, which is essential for overwintering. However, there can be a tradeoff between excellent fall vigor and too much fall growth, and this usually has to be managed by agronomic practices such as planting date and seeding rate. Planting later to take advantage of vigor may present challenges with winter survival if weather conditions are not favorable for fall growth, which was the case for many in central and southern Kansas.
The K-State Canola Breeding program has been selecting for cultivars that avoid fall stem elongation regardless of the planting date or seeding rate and this often translates into better winter survival. These cultivars have prostrate fall growth which keeps the crown (growing point) more protected at the soil surface. This trait could be especially useful in years when soil moisture conditions are ideal for planting but the calendar indicates it is too early to plant. We hope to broaden the planting window by planting these cultivars earlier while avoiding the risks of fall stem elongation and winterkill.
K-State agronomists continue investigating production practices to help manage fall vigor and growth. We have recently completed studies evaluating seeding rate by cultivar (open pollinated vs. hybrid) in narrow and wide row spacing (9-in and 30-in). In these studies, winter survival was greater with reduced seeding rates, and yield was similar to that achieved with higher seeding rates. In narrow row spacing, seeding rates around 275,000 seeds per acre were optimal for hybrids and seeding rates around 375,000 seeds per acre were optimal for open-pollinated varieties. In wide row spacing, seeding rates should not exceed 300,000 seeds per acre for both hybrid and open-pollinated varieties.
We are evaluating different plant growth regulators and their ability to help manage fall growth. Using plant growth regulators to manage fall growth in winter canola is a common practice in major winter canola growing regions. In addition to the products, we are evaluating at what growth stage and at what rate do we apply these products in the fall.
We are evaluating the effects of planting systems (planter vs. drill) under different seeding rates to better understand the effects of planting conditions and optimal number of plants under different soil and productivity environments.
Lastly, we are conducting a synthesis and review analysis to identify the main weather and genotype factors affecting winter survival in canola.
Having too little or too much fall growth in winter canola depends on an interaction of the cultivar chosen, management practices, and the weather. Predicting the weather is challenging enough and this can be stressful on producers. Through breeding and production research at K-State, we hope to find improved ways to manage these risks in winter canola.
For addition information on canola production, please refer to the recently revised “Great Plain Canola Production Handbook” available through K-State Research and Extension. https://www.bookstore.ksre.ksu.edu/pubs/MF2734.pdf
For more information about canola growth and development stages, please consult the K-State Canola Growth and Development poster: https://www.bookstore.ksre.ksu.edu/pubs/MF3236.pdf
Mike Stamm, Canola Breeder
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist