Factors involved in fall growth of canola
Establishing a canola stand at the optimum planting date is the most critical step to achieving uniform stand and consequently, high yield. Winter canola that is planted on time, at even planting depth, and in good soil moisture has the greatest potential for rapid establishment and the greatest ability to achieve the desired amount of above- and below-ground biomass for overwintering.
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 optimum winter survival, a winter canola plant needs 5 to 8 true leaves, 6 to 12 inches of fall growth, and an extensive root system. Hardened winter canola can withstand temperatures below 0 degrees Fahrenheit.
Figure 1. Winter canola at the appropriate size for overwintering. Photo by Scott Dooley, K-State Research and Extension.
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.
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: (1) the crop was planted too early or seeded at higher-than-optimal plant populations, (2) excessive soil fertility is present, (3) an unusually warm fall persists, or (4) a combination of any of these factors.
For instance, 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 is elevated above the soil surface, the chances for winterkill are increased.
Figure 2. Winter canola plot in mid-October, 2014. Early planting and warm temperatures have resulted in more than 20 inches of fall growth. Photo by Mike Stamm, K-State Research and Extension.
Figure 3. High plant populations in a winter canola plot in mid-October, 2014. Competition for light places the growing point well above the soil surface. Photo by Ignacio A. Ciampitti, K-State Research and Extension.
Another factor in stem elongation and winter survival is the amount of surface residue present in the seed row. 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. This residue management (related to quantity and even or uneven distribution) greatly benefits winter survival.
Planting dates in 2014
Many canola producers seeded winter canola earlier than normal this year because soil moisture was ideal for planting. Early seeding made sense because some canola did not achieve adequate growth to survive a colder-than-normal winter in 2013-2014. Warm October temperatures have led to significant growth -- and in some cases what we would consider too much fall growth. The figure below portrays strikingly different high and low temperatures for mid-October comparing 2013 vs. 2014 (Figure 4). Up until this weekend (10/25/2014), there have been no hard freeze events. Temperatures at or below 28 degrees F will cause the plant to wilt and slow growth.
Figure 4. High and low temperatures from 2013 and 2014 at Manhattan. Mid-October temperatures were significantly warmer in 2014. Source: Kansas Mesonet, K-State Weather Data Library.
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 being dominated by open-pollinated (OP) varieties to hybrids. Hybrids tend to have greater fall vigor because of larger seed size. Fall vigor is important because it results in rapid establishment and root growth. However, with hybrids and certain OP varieties, there can be a tradeoff between 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 fall vigor may present some challenges in terms of winter survival if weather conditions are not favorable.
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 greater winter survival. This trait could be especially useful in a year like 2014 when soil moisture conditions are favorable but the calendar indicates it is too early to plant canola. In addition, we hope to broaden the optimum planting window by planting these lines earlier while avoiding the risk of too much fall growth.
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 to 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.
Figure 5 shows three entries from the National Winter Canola Variety Trial. The stake represents the soil surface while the red arrows point to the canola plant’s growing point. The hybrid on the left was developed in the European Union (EU) and is exhibiting about 2 to 3 inches of fall stem elongation. 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 was developed in the EU and it possesses the semi-dwarfing trait. Depending upon the weather this fall and winter, we would expect the hybrid on the left to be more susceptible to winterkill because of the elevated crown.
Figure 5. Varieties exhibiting differences in fall stem elongation in the National Winter Canola Variety Trial at the North Central Experiment Field, Belleville. Photo by Mike Stamm, K-State Research and Extension.
K-State agronomists are undertaking several research studies 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, 20-in, and 30-in). In collaboration with private industry, we are evaluating plant growth regulators and their ability to help manage fall growth. Using plant growth regulators 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?
Predicting the weather is challenging enough and having too much or too little fall growth in winter canola greatly depends upon the weather conditions in the fall. This can be stressful on canola producers. Through breeding and production research at K-State, we hope to find improved ways to manage this risk.
Mike Stamm, Canola Breeder
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist