Herbicide resistance is a topic that comes up at every spray stage of the growing season – pre-burn, in-crop, pre-harvest and post harvest. This is a common theme for good reason; Herbicide resistance decreases profitability for every farm it occurs on. This reduction in profitability stems from an increased need for management, herbicide applications, integrated practices, increased competition from weeds, down graded samples and more. So what steps for 2015 can be taken to manage herbicide resistance?

Utilize scouting apps and data management platforms

The very first step to take is scouting your fields, staying in front of agronomic occurrences and making observations that get documented and saved for long term reference. Understanding the resistance risk in detail is going to keep resistance away from your operation.  Identifying the problems before they manifest are a must; If you see abnormal pockets of weeds not dying, GPS reference that spot and be sure to check it after a sequential herbicide application or test it for resistance once the weeds have set seed. You can monitor how far that spot has moved in the following years, if at all.

This will let you know if you are using the right management practices. Having the records of what products, active ingredients and groups of have been applied helps you make an informed decision every time your sprayer runs over that field. An intriguing finding in one study was that it didn’t matter if there was herbicide resistance surrounding your fields or not, the incidence of resistance was always a product of the management practices on each specific field. This tells us that we need to focus on strategic practices on our own land, and not worry about what our neighbour is or isn’t doing.  It is good to be aware of what’s going on in the fields next to you, but ultimately proper management is going to make the difference on your farm.

Tank mix and rotate groups

There is often discussion about whether rotating groups yearly or tank mixing groups is the best for resistance management. In a study it was shown that a grower who had used on average 2.5 modes of action (MOA) per application was 83 times less likely to have resistance than those who used 1.5MOA on average (Source: http://www.agprofessional.com/news/using-farm-data-slow-evolution-herbicide-resistant-weeds). This shows that using 1 extra MOA per application significantly decreases your risk of having resistance. If you mix upwards of 3 modes of action consistently, and also rotate groups yearly then you are taking two steps in the right direction. The one thing that doesn’t get stressed enough is looking at the efficacy data on which actives you are applying on the weeds you are targeting, ensuring that all the actives/groups have activity on the target weed population. For example, applying a group 1, 4, 6 tank mix to try and manage resistant wild oats is not effective since the only group with activity on wild oats in that mix is a group 1.

In some areas of the world herbicide resistance is the limiting factor in crop production; In western Canada we still have the opportunity to get creative and use data, use unique practices and learn from other areas of the world to decrease the resistance risk. The cost of management to keep resistance at bay is more inexpensive than the management practices that need to be deployed once resistance is spread across your farm.


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