GT soybeans - be sure to spray a residual herbicide at or before planting

Sunday, March 8, 2015

Last year, Ontario growers lost an estimated two bushels an acre because they did not spray early enough. That cost Ontario some $60 million in lost revenue

by PAT LYNCH

In September 2013, I spoke to soybean growers in South Africa who had between 200 and 25,000 acres each. They are just getting into soybean production there and I asked them if they could see weeds in their GT soybeans when the soybeans were at first trifoliate. About 10 per cent of the hands went up. I then asked if they saw weeds in their neighbours' soybeans when they were at the first trifoliate. About 75 per cent of the growers raised their hands.

I told them that I get the same response from Ontario growers. The reality is that if you see weeds either dead or alive in a soybean field, you have lost yield. Research suggests that you lose one bushel an acre for every inch of weeds. Other research shows that weeds can grow one to two inches in between two and four days. You lose a lot of soybeans if you do no control weeds early.

Last spring, when I drove around Ontario, I felt a sense of failure. In 2011, I set out to have all GT soybeans sprayed with a residual herbicide. I figured that spraying residual herbicides in GT soybeans would follow the route that it had in GT corn. Practically all GT corn receives a residual herbicide.

The latest surveys for 2014 suggest that about 25 per cent of Ontario's soybean acres have a residual herbicide at planting. A further 10 per cent have a residual herbicide post-emergent. These numbers are too low. Last year, I figure growers lost at least two bushels an acre across Ontario. At a price of $11 per bushel; this represents $22 an acre in lost revenue. With Ontario's three million acres, that represents over $60 million in lost revenue.

So what is the solution? You must spray a residual herbicide at or before planting. My friend and peer Paul Sullivan CCA (ON) in eastern Ontario believes growers should be spraying before planting GT soybeans. Last spring, when it was too wet to do any field work, he encouraged his customers to spray their soybean fields. He feels that this was a great strategy. Those fields that were sprayed were a lot cleaner than fields that were sprayed just at planting – and a lot cleaner than fields that were sprayed after planting.

There are a lot of herbicides to choose from. The basic ones are Dual II Magnum or Frontier, which are sold in packages such as Boundary and Integrity. Other good products for the common weed spectrums are Broadstrike, Classic and Valtera. Each one of these products is strong on specific weeds. I like residual products that can control ragweed, lamb's quarters, nightshade and fleabane.I believe these are the weeds that will become resistant to glyphosate. Individual farms have individual problems.

And for those of you who believe that you will not get GT fleabane, good luck. It has been identified across much of Ontario and will be coming to a farm near you. You must put together a strategy now to control it. Plan a program as if you already have it. BF

Consulting agronomist Pat Lynch, CCA (ON), formerly worked with the Ontario agriculture ministry and with Cargill.