By Mike Stamm, Ignacio Ciampitti, Kraig Roozeboom, Gary Cramer and Mary Knapp
Fall temperatures in Kansas have once again been warmer than normal. The unusually warm weather has now extended into November. 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 (Fig. 1). 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 optimum 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 Fahrenheit 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, and stem elongation above the soil surface.
Figure 1. Winter canola near Concordia, Kan., at the appropriate size for overwintering.
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 (Fig. 2)
- The crop was seeded at higher-than-optimal plant populations (Fig. 3)
- Excessive soil fertility is present (particularly nitrogen)
- An unusually warm fall persists (the main cause this year)
- 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, or crown, close to the soil surface, especially in no-till cropping systems. Appropriate residue management (any way to remove residue from the seed row) greatly benefits winter survival.
Figures 4a and 4b show what can happen when residue blows back into the seed row following planting into heavy corn residue. Because of residue in the seed row, the canola hypocotyl in this case is etiolated, or overextended, and thus vulnerable to freezing temperatures and other biotic stresses. Etiolation is when a plant develops in partial or complete absence of light.
Under these conditions, plants will have long, weak stems and a pale color. In the situation shown below, the canola hypocotyls grew upward through the corn residue, stopping when they reached sunlight above the soil surface. That is where the rosettes were established. As a result, the crop easily succumbed to cold temperatures, and the field in this specific example was lost because of poor residue management.
Planting Dates in 2016
Soil moisture conditions dictated planting dates for winter canola in 2016. Adequate soil moisture allowed for early planting in central, west central, and southwest Kansas. In these areas, some canola has become excessively large. This, in combination with warmer-than-normal fall temperatures, puts the crop at increased risk for winterkill, especially if temperatures drop off rapidly and the crop does not have adequate time to winter harden. A slow, gradual cool-down with mild freezes would greatly benefit the crop.
Other areas of Kansas (south central) had adequate to surplus soil moisture this fall for planting. In some cases, planting was delayed because of wet soils and in other cases producers had to replant their crops following heavy rain events. The concern there is that the crop may be too small heading into the winter months. However, the warmer-than-normal temperatures and one-month temperature outlook (Figure 5) give us confidence that the crop will be able to grow sufficiently for overwintering (Fig. 6).
The high and low temperature trends for 2016 are much above normal for Manhattan (Fig. 7). Mid- to late-October was very warm with temperatures approaching freezing only one time. Temperatures are trending very similarly to the fall of 2015 when we had a warmer-than-normal fall and winter with little to no winterkill observed in winter canola. A slow decline in temperatures this fall would be ideal for achieving adequate winter hardiness in 2016. This is important as the canola crop should begin to winter harden this time of year. Low temperatures at or below 30 degrees F are essential for winter hardening.
Varietal differences exist for traits such as fall vigor, the ability to avoid fall stem elongation, and winter survival. More hybrids are being grown each year, and the industry will one day switch from open-pollinated (OP) varieties to hybrids. Hybrids tend to have quicker establishment in the fall than OP varieties because of hybrid vigor.
Figure 5. One-month temperature outlook shows warmer-than-normal temperatures are predicted to persist through November.
This is important because it results in rapid plant development for overwintering. However, with hybrids and certain OP varieties, 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 hybrids later to take advantage of improved vigor may present some challenges in terms of winter survival if weather conditions are not favorable for fall growth.
The K-State canola breeding program has been selecting for lines that avoid fall stem elongation regardless of the planting date or seeding rate. These lines have prostrate fall growth and this often translates into better winter survival.
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. In addition, we hope to broaden the optimum planting window by planting these lines earlier while avoiding the risks of fall stem elongation and winterkill.
Another tool under development by private industry and being evaluated by the K-State canola breeding program is the semi-dwarfing trait, or low-biomass-producing trait. The semi-dwarfing trait also helps keep the crown closer to the soil surface regardless of planting date or seeding rate. We have seen enhanced winter survival in hybrids that possess this trait.
Fig. 8 shows three entries from the National Winter Canola Variety Trial. The stake represents the soil surface while the yellow arrows point to the canola plants’ growing points. The hybrid on the left was developed in the European Union (EU) and is exhibiting about 2-3 inches of fall stem elongation (or crown elevation).
The variety in the center is an experimental line from the K-State canola breeding program, showing no stem elongation. The hybrid on the right possesses the semi-dwarfing trait and it is showing only slight crown elevation. We would expect the hybrid on the left to be more susceptible to winterkill because of the elevated crown.
Kansas State agronomists are investigating production practices to help manage fall vigor and growth. We have studies evaluating seeding rate by variety (OP vs. hybrid) in narrow and wide row spacing (9-in and 30-in).
In the first year of the studies, we did not see consistent differences in winter survival among the cultivar by seeding rate interactions because the winter temperatures were warmer than normal. However, in several cases, winter survival was greater with reduced seeding rates, and yield was similar to that achieved with higher seeding rates.
In collaboration with private industry, we are evaluating plant growth regulators and certain fungicides and their ability to help manage fall growth. Using plant growth regulators and fungicides in winter canola is a common practice in the EU. Other questions we want to address through these studies include: How far can we reduce seeding rates and remain profitable? How do varieties respond to different seeding rates? What is the optimum seeding rate for a given row spacing by variety interaction? At what growth stage and what rate do we apply growth regulators to manage fall growth?
Having too much or too little fall growth in winter canola depends on an interaction of the variety chosen, management practices (primarily related to planting date, seeding rate, and row spacing), and the weather. Predicting the weather is challenging enough and this can be stressful on canola producers. Through breeding and production research at Kansas State, we hope to find improved ways to manage these risks.