Does a January thaw mean wheat problems? | TSLN.com

Does a January thaw mean wheat problems?

Bob Fanning
SDSU Plant Pathology Field Specialist

The recent, warm weather has been a nice break from the cold temperatures of early January, but is it good for the wheat crop? A couple of wheat producers were recently discussing potential concerns with the green tint showing up in area winter wheat fields due to the warm weather. The discussion got one of the farmers wondering what effect the warm temperatures were having on his dormant planted spring wheat.

Dormant seeding is when a crop is placed in a soil long before soil temperatures and/or moisture conditions are going to allow the seed to germinate and grow. The reasons for considering this technique is to assure early seeding of cool-season crops like spring wheat where it is important to avoid hot weather that occurs when they are planted too late in the spring. It also helps to spread workload.

Ideally, dormant seeding is done when soils are dry and/or near freezing, and the combination of moisture and temperature adequate to germinate the seeds will not occur until late winter or early spring. If everything works right, the seeds don't germinate until temperatures conducive to injuring or killing the young seedlings are unlikely. There is some risk with dormant seeding, but it has been done successfully at research stations and area farms.

With the calendar still on January, and severe cold still possible this winter, the farmer ventured out to his dormant planted spring wheat to see how it was faring. Not only were most of the kernels taking on moisture and swelling, but many were beginning to sprout. The question is, will cold temperatures kill the newly sprouted spring wheat? A definitive answer seems to be difficult to come by, but a respected agronomist advises to avoid being concerned just yet. If the crop is damaged, producers will know early enough to replant or plant fields to another crop. Thin and bare areas in a dormant planted spring wheat field could be thickened up in the spring without the concern of mixed wheat. There would likely be variation in heading and maturity however.

About the winter wheat fields that are showing green? To truly break dormancy, soil temperature at the crown level must rise several degrees above freezing, although as soil temperatures approach 48 degrees F, the process occurs quickly. In other words, the "green tint" in winter wheat fields may be a bit deceiving and the plants haven't likely fully de-hardened.

The concern of course, is if dormant planted spring wheat develops a significant sprout, and/or winter wheat breaks dormancy, at which point it has roughly the same cold tolerance as spring wheat, and then gets severely cold. Research from Canada suggests that "unacclimated" spring or winter wheat has a minimum survival temperature of 27.5 degrees F. Spring wheat actually has some ability to "acclimate" to cold temperatures, but as with winter wheat, it takes some time, and can never tolerate the low temperatures that winter wheat can.

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At this point, it is impossible to tell if either dormant planted spring wheat or winter wheat is in jeopardy, but there is reason to be optimistic, and motivation to watch soil temperatures in the coming weeks.