Encourage tillering | Apply adequate nitrogen as soon as possible and consider weed control
Call it a rite of spring: winter wheat emerges from its blanket of snow and agronomists caution farmers not to make hasty decisions if emergence is poor.
“In all situations, you’re going to have a variable winterkill pattern in the field,” Brian Fowler told an April 24 webinar organized by Ducks Un-limited.
The University of Saskatchewan plant science researcher said conditions in some parts of the Prairies are worrisome, given early snow last fall that may not have allowed soil to freeze. That could lead to higher winterkill, although winter wheat stands do tend to surprise farmers with their ability to tiller and fill in the bare spots.
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Fowler said it takes only eight to 10 centimetres of snow to insulate a winter wheat crop and keep the crown temperature at comfortable levels. Much of Saskatchewan and central and northern Alberta achieved that depth.
However, that same snow may create additional risks to the crop, including snow mould and a later maturing stand that could be exposed to fusarium head blight.
Fowler said snow mould risk is highest in areas where the snow is deepest and packed down, usually on field edges.
Snow mould can kill winter wheat, but it is difficult to determine the degree because evidence of mould quickly disappears.
“I have not seen snow mould to be a very high risk factor when we have gone to low till seeding,” Fowler said.
That’s because snow in standing stubble is usually not tightly packed.
The fusarium threat won’t be known until the crop begins to flower.
Ken Gross, a Ducks Unlimited provincial agrologist for Manitoba, told the webinar that winter wheat could be exposed to fusarium if late snow melt appreciably delays emergence.
Ordinarily the crop flowers before fusarium spores become a problem.
As well, winter wheat will produce more tillers if there is considerable winterkill, which mature later and extend the flowering period.
“It could broaden the window (for fusarium),” Gross said.
Plant disease specialist Ron Howard of Alberta Agriculture said in a later interview that heavy snow may also allow more fusarium inoculum to survive over the winter, but weather conditions at the time of flowering will be the primary factor.
Risk also depends on whether the winter wheat was seeded in or near a crop that had fusarium last year.
Flooding of winter wheat fields is another risk many will face this spring.
Fowler said well established plants will better tolerate flooding. Cold, moving water does less damage to the crop than warm, stagnant water.
Plants that are completely submerged are at higher risk than those with leaves above the water, he added. And green leaves are not necessarily an indicator of plant survival. New white roots are definitive evidence.
Gross recommended early nitrogen application to maximize potential once winter wheat survival is known.
“Human nature is to sit and wait and see what it does.… That’s exactly the wrong thing to do,” he said.
“You have to feed the crop when it’s struggling to encourage that root tiller development.”
Nitrogen should be applied as soon as farmers can get into the field and ideally before the four- to five-leaf stage, said Gross. A three-week delay in application can reduce yields by 30 percent.
Nitrogen deficiency reduces tillering, and early tillers contribute more to yield than those formed later in the season.
He also cautioned against the common tendency to use spring wheat nitrogen rates on winter wheat.
Winter wheat has a yield advantage over spring wheat, so it needs more nitrogen to reach its potential.
Gross recommended early weed control. Winter wheat will often outcompete wild oats, but spraying might be necessary if the crop is patchy.
“You’ve got to get out there and scout early and don’t wait to spray.”
