After a stretch of cool, wet weather many corn fields across Ontario have turned yellow, and growers are asking whether it's safe to spray the stressed plants.
Retired University of Guelph weed scientist Dr. Peter Sikkema says the reason that corn is tolerant to many herbicides is its ability to rapidly metabolize those herbicides. However, when the plant is stressed it will metabolize the active ingredient more slowly, which leads to greater crop injury.
At a Ridgetown agribusiness breakfast meeting on Tuesday, Sikkema said making the decision to spray in poor conditions "is a super hard one to call. I think if you spray under these conditions, chances are you're going to have more injury." But if growers delay spraying and wait for better weather, they'll see great yield loss from growing weed pressure.
"You're stuck between a brick and a hard place in terms of making that decision," says Sikkema. He thinks it's best for growers to make spraying decisions on a field-by-field basis. "If your weed pressure is low, I would probably wait. If you have heavier weed pressure, it becomes a more difficult decision."
Both Sikkema and RealAgriculture agronomist Peter Johnson are recommending growers take a look at the crop safety ratings of the herbicides they intend to use before spraying. For growers with a lot of acres to cover, and the potential for more rain this week, Johnson has been recommending his clients use products with high crop safety rating and get the fields sprayed.
"Some of the corn is going white after it, but I'm quite convinced it will recover. I've seen it before," says Johnson. "I think the yield loss potential due to weed interference trumps the phytotoxicity concern over the safer products, things like mesotrione. They'll bleach it white, but they're really quite safe most of the time.
"We sprayed some corn when we had a window, and the corn definitely felt the spray, but the weeds are now gone, and that corn is coming back to the yellow colour that all the other corn is. It did go white, but it's come back," notes Johnson. "I really think that the stress from the herbicide is real, but generally speaking, it recovers. And so far, without any yield data, it looks like it is recovering well."
Johnson says under these conditions he's telling his clients to stay away from dicamba products "just because their crop safety is good but not excellent."
Agronomist Marijke Vanderlaan and her colleagues at Syngenta Canada are sharing a similar message with the growers they work with. With more rain coming, she feels confident in recommending growers spray Syngenta products that have strong crop safety ratings: "the weeds would be worse," she says.
Vanderlaan also noted that warmer temperatures on Monday and Tuesday and a forecast for higher temperature later in the week make spraying as soon as possible the right decision.
