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MikeStamm K-State Canola Breeder mjstamm@ksu.edu

Wintersurvival of canola in Kansasis a complicated issue. Winter stand losses can be caused by one or moreabiotic and biotic stresses, including poor plant establishment, lowtemperatures, wind desiccation, dry soils, soil heaving, and damage by diseasesand pests. A cultivar's freezing tolerance, its ability to cold harden, and itsinteraction with the environment ultimately determine whether a crop willsurvive the winter.

Using goodfarming practices is the best way to insure the survival of a winter hardycanola variety. Canola that is planted on time and in adequate soil moisturehas the greatest potential. Six to 8 true leaves and 6 to 12 inches of fallgrowth should be present prior to winter dormancy. The dormancy period is whenwinter canola is most tolerant to cold temperatures. During this stage, therosette should be at the soil surface with no visible stem elongation. A rootdiameter of about 2 cm and an extensive rooting system are also beneficial.

Severalquestions have been asked about whether the 2013-2014 canola crop is going tosurvive the winter. Survival will likely depend upon the cultivar grown, plantgrowth in the fall, planting date, and the severity of winter. Canola that iswell established with a thick crown and robust root system has the greatestchance to survive a cold winter. Canola that emerged late with a weak rootsystem is at the greatest risk for winter kill.

The winter hardeningprocess

In order tosurvive the winter, canola must go through a hardening process. This begins inthe rosette stage in the late fall after several days of near-freezingtemperatures (about 35F). At these temperatures, plant growth is slowed, resultingin smaller cells with a higher concentration of soluble substances moreresistant to frost damage. A few hard freezes (about 26F) are beneficial tohalt leaf growth and promote hardening. Longer acclimation periods with fewerdramatic swings in temperature are beneficial to hardening and increasefreezing tolerance in plants. It's at this stage when canola takes on anoverwintering appearance. This is a natural process as top growth is lost.

For canolathat had adequate fall growth, the cooler December should have providedsufficient winter hardening. This canola should withstand the temperaturefluctuations we are experiencing as of late. Hardened winter canola can endurea certain amount of time with temperatures at or below 0 F, depending on thecultivar. However, extended periods of temperatures at or below 0 F withoutsnow cover may be detrimental to survival. Winter survival should improvewhenever snow cover is present.

Factors involved inthe "un-hardening" of canola

Ultimately,it may not be the cold temperatures per se that cause winter kill but the rapidfluctuations in temperature, which can be a common occurrence in Kansas during thewinter. "Un-hardening" of canola is accelerated when temperatures increase to60F or above for an extended period of time (approximately 2 weeks).Un-hardening is a loss of freezing tolerance. However, the effect offluctuating temperatures and un-hardening during the winter is complicated.

Researchconducted by K-State indicates winter warming trends can actually have apositive effect on winter survival in some ways. Green leaf tissue may have increasedmetabolic activity, rejuvenating the overwintering plants. This partly explainswhy plants growing in the field can survive colder temperatures than plantsacclimated at continuous cold temperatures in a controlled environment. If thewarming trend is followed by a gradual cool down and no stem elongation occurs,then plants can re-harden. In addition, as long as low nighttime temperaturesaccompany high daytime temperatures, the rate of un-hardening should be slowed.


Assessing wintercanola stands

Although itis too soon to say that the canola crop is no longer in danger of stand loss,producers can still evaluate their stands for winter kill this time of year.Normally, winter survival is assessed visually after the danger of furtherstand loss has passed, which is usually mid-March in Kansas. When evaluating winter survival,look for green leaf tissue at the center of the rosette or crown. If green leaftissue is present and the crown is firm when squeezed, it is likely the cropwill resume active growth as temperatures rise and day length increases. Theroot may be examined as well for firmness and vigor. Also remember that thebranching ability of canola allows it to easily compensate for stands wheresome winter kill is observed. A harvest population of four to 15 plants persquare foot is optimum; however, a stand of one plant per square foot isacceptable although yield potential will be reduced.

In thepicture below, winter kill was observed in a variety trial near Enid, OK.Heavy rainfall following planting reduced stands and delayed emergence,resulting in smaller than normal plants. Thus, the smaller plants weresusceptible to winter kill. The green plants in the picture are still alive.Other varieties in the trial showed better winter hardiness.

Winter hardinesstraits in canola cultivars

To increasecanola's consistency in the region, the canola breeding program at K-Statecontinues to select for winter hardiness traits. Breeding accessions possessinglonger vernalization periods are being crossed into the germplasm pool. Onetheory on improving winter hardiness is that canola can harden more easilyafter a winter warming trend prior to the vernalization requirement beingreached. Therefore, extending the vernalization requirement may allow plants towithstand more variations in temperature during the winter months.

Winterhardiness remains an important trait to consider when selecting a cultivar forany canola cropping system. Differences exist, however, so decisions should bebased on results from multiple years and locations. We have not experiencedconditions that promote widespread winter kill for a couple of years, soproducers may need to review data from 5 or 6 years ago to help with varietydecisions. Remember that there are other factors to consider when selecting avariety or hybrid including: yield potential, seed oil content, maturity,lodging tolerance, disease resistance, and herbicide tolerance to name a few.

Summary

Winter survivalwill depend on soil moisture at planting, planting date, and the varietyselected. When scouting your canola periodically this winter, check for agreen, healthy crown. If you find that, then expect the crop to survive.Regrowth will begin when average daily temperature is 40 F or greater and daylength increases in the spring.

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