Wheat Pete's Word, Aug 15: Corn disease risks, a sudden potash deficiency, and cloudy conditions


As the summer days stretch and the forest fire smoke settles in over huge areas of the country, farmers are wrapping up wheat harvest in the east and starting harvest in earnest in the west.

Late-season agronomy typically centres on harvest management, but diseases and insects are still lurking, especially in the corn crop. In this week’s Wheat Pete’s Word, host Peter Johnson talks threats to corn, sudden potash deficiencies and what to do about them, and tackles some cover crop and late-season weed management. (Summary continues below)

Have a question you’d like Johnson to address? Or some yield results to send in? Leave him a message at 1-888-746-3311, send him a tweet (@wheatpete), or email him at [email protected].


  • Keep the crop reports coming! In Eastern Ontario, a 196 acre soft red winter wheat field went 107 bu/ac on  average, and that’s with 10 acres having 50% winterkill. Add in the 5 to 6 bales of straw per acre, and that’s a darn nice field
  • Upcoming events: Don’t miss out on next week’s Soil & Crop summer tour stops. Find more here.
  • Weather update: We are about 100 heat units ahead of normal in Ontario, with is not really incredible, and only amounts to about 4 days. The difference, really, is that the heat has been combined with extremely dry weather. Some edible beans will be ready by the end of the month. Soybeans are well ahead of average, and that’s good news to get the winter wheat planted on time (ie. early)
  • Saskatchewan got down right cold this last week — down to 3 degrees!
  • It’s been cloudy, cloudy, cloudy in some areas. Total sunlight doesn’t have a huge impact pre-tassel, but it does have an impact at silk timing, and a rather large one if it’s cloudy during grain fill. That can add up to a 21% yield hit, research shows.
  • Many are observing fewer rows around on cobs to the tune of two rows fewer than normal. You can make up that yield if you have longer cobs and good grain fill, so we will keep an eye on it.
  • Disease levels in corn may surprise you this year, even though it was so dry. Because we finally got water at silking and the humidity has been high, we could see higher levels of fusarium and gibberella. Tight husks may also end up being an issue, which can make a bad problem worse.
  • Does cob set height indicate yield potential? There’s a relationship, for sure, but it’s not a one-to-one ratio. Remember the 50/50 rule of stalk to grain. A thin, short stalk is going to relate to lower overall yields, but not purely because of height.
  • A farmer noticed that the barley is super short and  the barley heads barely cleared the flag leaves, which are standing straight up. What happened? Hot, dry weather prevented the head from extending.
  • Low pod counts on soybeans — usually we see the highest number of pods per node in the middle of the plant, but in really dry areas we’re seeing only 2 pods per node, and the tops of plants haven’t made up for the difference, even though the water came at a decent time. Seeds that are there are large and may be plump, but it will have a yield impact.
  • Potash deficiency came all of sudden — where did it come from? Yup, you can likely blame dry weather. But get out to check for soybean cyst nematode. And soil test! Ideally you want 100-120 ppm, apply and build after wheat levels after wheat and get the job done.
  • Poor clover after wheat, can I put oats in? Call Agricorp first and file a damage report, then broadcast or drill in the oats, you cannot work the ground. Whether you get a payout or not isn’t the most important thing, it’s that you get something growing and now is the time. Cover those fields!
  • Broadleaf weeds in clover — control that fleabane!
  • Bindweed in wheat stubble? Get the problem weed book from Mike Cowbrough, OMAFRA weed specialist (or here). You need a tank mix.


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