Last year’s dry spell, this year’s herbicide residue

Will imi herbicide carryover strike again in 2019?

Canola growers in central Saskatchewan who had used Odyssey® herbicide in 2017 were the first to realize something was wrong.

In spring 2018 I received a number of calls from farmers who were seeing delayed, weak canola seedlings, which they could not explain. Similar calls followed from those who had sprayed other “imi” herbicides. 

In some areas, it’s not an uncommon practice for growers to follow the off-label practice of spraying Odyssey (active ingredients imazamox & imazethapyr), then seeding canola on the same field the following spring. It’s even more common to spray Solo® (imazamox) on lentils or Viper® (imazamox) on peas then seed canola on the same field the next year. Farmers have been doing it without issue for years.

The difference this time around was that during the key period of June, July and August 2017 they did not receive much, if any, rainfall. I finally put it all together when I learned what they all had in common. With dry conditions, there is less microbial activity in the soil, and imi herbicides are broken down by soil microbes. Therefore the dry previous growing season caused carryover of the herbicide to 2018. Canola is the most sensitive to the carryover, followed by cereals and pulses.

It may not seem like a big deal, but consider that Viper is the only in-crop herbicide registered for peas and Solo is one of two products registered for lentils.

That means 2017-18 was a tough lesson, and there’s only one course of action to recommend going forward. If you’ve sprayed imazamox on pulses, seed a cereal or Clearfield® canola the next spring. These may not be our favourite options, but they are the best options.

Once again in 2018 parts of Saskatchewan experienced very little rainfall in that critical June through August period. This year farmers can carefully adjust their rotations if they believe it’s necessary. Those still in doubt can send soil samples away to have them checked for residues. The drawback is that you will get a report of residue levels, but it may not be meaningful, as no one has yet established a “safe” residue level.

 If you’d like to learn how this issue affects you, contact your Cargill representative.

 Always read and follow label directions Odyssey, Solo, Viper and Clearfield are registered trademarks of BASF Canada.