As temperatures fall, what factors influence the survival of winter canola?
There was a narrow window for planting winter canola in fall 2018, starting with September rains and ending with heavy rains in October. Luckily, the September rains set the stage for favorable conditions for stand establishment. Soil moisture aids rapid emergence of canola, which is critical in attaining the right amount of top growth heading into the winter months. How could this, and other factors, affect the winter survival of canola?
Effect of canola 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. For the greatest winter survival, a winter canola plant needs 5 to 8 true leaves, 6 to 12 inches of fall growth, a root collar diameter of ¼ to ½ inch, and an extensive root system. 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 20 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
- The crop was seeded at higher-than-optimal plant populations
- Excessive soil fertility is present (particularly nitrogen)
- An unusually warm fall persists
- Selection of a poorly adapted cultivar
- A combination of any of these factors
For example, 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. K-State research has shown that residue removal from the seed row is important for keeping the rosette close to the soil surface, especially in no-till cropping systems. Appropriate residue management (any method to remove residue from the seed row) greatly benefits winter survival.
Planting dates in 2018
Soil moisture conditions once again dictated planting dates for winter canola in 2018. September rains made soil moisture conditions ideal for planting (Figure 1), compared to 2017 when dry soils delayed planting. The biggest issue with planting canola in fall 2018 was waiting on soils to dry out. This could have delayed planting beyond the optimum window for some producers.
Figure 1. Winter canola plots were seeded into a stale seedbed with highly favorable moisture conditions near Kiowa, KS on September 24, 2018 (Photo by Mike Stamm, K-State Research and Extension).
Where canola was seeded on time, we are seeing adequate fall growth and there should be little initial concern for this crop going into the winter (Figure 2). As temperatures remain in the 50s and 60s with lows above freezing, this crop will continue to add leaf area before repeated hard freezes move it into dormancy.
Figure 2. Canola plots near Kiowa, KS on October 23, 2018. These plants have four true leaves and are continuing to add leaf area (Photo by Scott Dooley, K-State Research and Extension).
Temperatures have been cooler recently and warmer temperatures would actually benefit late-planted canola. We have already seen the first hard freeze of the season around October 15. Cosmetic damage to leaves (bleaching) and even plant loss has been observed where temperatures dropped below 28 degrees F for several hours. Plant loss would be the biggest concern on canola with 2 or fewer true leaves. At the South Central Experiment Field near Hutchinson, planting was delayed until September 28 because of wet soils (Figure 3). This is about a week later than when we would typically seed canola at this field. This plot is at the greatest risk for winter stand loss because of the current plant size.
Figure 3. Winter canola stands at the South Central Experiment Field, Hutchinson. These plants are smaller-than-normal for October 23 (Photos by Scott Dooley, Mario Secchi, and Ignacio Ciampitti, 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 probably 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. 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 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. Hybrid cultivars tend to have quick establishment in the fall because of hybrid vigor. This is an important trait because it results in rapid plant development for overwintering. However, there can be a tradeoff between good 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.
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 are 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.
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 the European Union (EU). In addition to the products, we are evaluating at what growth stage and at what rate do we apply these products in the fall.
Lastly, 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.
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:
Mike Stamm, Canola Breeder
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist