Wheat Pete's Word, May 13: Cold soil, sulphur deficiency, and assessing freeze damage on wheat


The weather feels more like mid-April than mid-May, and many farmers in Ontario are worried about corn and soybean seed in the ground and wheat heads above ground.

There are reasons to be concerned, as nighttime temperatures over the last week have dipped very low and sometimes for the entire night. In this week’s Wheat Pete’s Word, host Peter Johnson sets out how to gauge the risk to already-planted seed, assess the potential damage done to wheat, and make the call on when to roll out again. Listen now, or download for later!


  • As we move through the planting and seeding season, we tend to rush. Be safe, please. Think twice, act once. Get some sleep when the weather breaks.
  • This last week was not a kind one for Ontario’s crops. Some areas saw as much as 7″ of snow (!!) and -5 to -7 degrees C for several hours. Ouch.
  • Ginseng growers rushed to cover plants ahead of frost, only to end up with snow loads so heavy the covers collapsed.
  • So, let’s get down to brass tacks. No matter what the crop, freeze/frost injury is a function of how cold it got, for how long, what kind of crop, and the stage of the crop.
  • For winter wheat, spring frost injury largely depends on where the head is at in the stem. In some areas, the head is likely 6″ above the ground, and the science suggests that should withstand -4 degrees C for two hours. But some areas saw colder than that for longer.
  • So, how do we tell a) where the head is and b) if it’s damaged? You’ll have to wait five to seven days to assess the damage, then cut open some stems.
  • Healthy heads will be light green and firm and turgid (full of moisture), but a damaged head will be limp and pure white.
  • What about alfalfa and red clover? Establishing alfalfa should be fine, as it’s been cool, and the plants are either not emerged or very small and quite frost tolerant. Again, it all depends on where the growing point is and how cold it was for how long. Regrowth on frost-damaged alfalfa will happen, but the growth will have to come from lower down from leaf axil or the crown, and that will really delay harvest.
  • That may be an issue for alfalfa/grass mix fields, as the grass is going to be ready far before alfalfa, if it was frost damaged.
  • If the soil is fit, plant…right? Well, yes, but that first eight, 12, 24 hours is so critical. That’s why we talk about the risk of a cold rain shortly after planting.
  • Thinking about the corn in the ground right now, even when frost gets down quite deep, the soil is warmer than air temp. In some areas, you’ll get 10 to 25 per cent of stand loss if you get 7-10 days of cold soil after planting.
  • Know your soil, know the forecast.
  • Sulphur response feedback, and split app N. Cold soil means decreased soil activity, and can induce an S deficiency
  • Manganese deficiency getting a top-up twice, because micros aren’t being released, either
  • Seeing strange symptoms on Branson wheat? We think it’s physiological fleck in the lower part of the canopy. Please send in photos if you see this.
  • Do we spray fungicide on the wheat crop right now? It depends on where you are, but really, there’s not enough growth and not enough disease pressure if you’re north of Stratford. Maybe in the deep southwest if the flag leaf is emerging. No flag? Park the sprayer (unless it’s for herbicide)
  • Terrible timothy can make money! Two hundred bales at $5/bale.

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