Written by: Lorie Smith, Georgian Central Regional Communication Coordinator

“What is a weed?” That was the first of many questions that Craig Reid, agronomy manager with Sprucedale Agromart, posed to the participants of the Integrated Weed Management (IWM) course at Grey Ag Services in February. A weed is a plant growing where it is not desired. Although we don’t often view it in this fashion, agriculture is a controlled ecological succession, from bare earth to the harvest of annuals or short-term perennials. Weeds fill voids in that succession, left vacant because of human actions. Craig commented that “Mother Nature hates bare soil, and she always bats last.” We need to accept that we are interrupting ecological succession in its tracks, and weeds are an integral part of the process. The process needs to be managed, not the weed. Further diversification of cropping systems and strategies are necessary to effectively manage plants growing where they are not desired.

Integrated Pest Management, or IPM, is an approach that many have heard of and implemented. The classic definition is the use of many different types of control methods, alone or in combination, to prevent pests from occurring, with chemical control being an option of last resort. There are five basic components: identification; monitoring; thresholds; methods of control; and evaluation. Integrated Weed Management takes the principles of IPM and applies them to a subset of pests – weeds.

Reid stressed that his definition of IWM has subtle differences but includes the same components. He believes that we should incorporate a combination of control methods and consider where in the process the chemical controls would be the most effective and cause the least disruption. Chemicals are part of the system, not an afterthought. Farmers also need to manage ecological succession. We have forgotten that agronomy is ecology. Reducing environmental and health risks needs to be considered as well, and we need to optimize profit over the short and long term.

In response to the IWM definition that Reid reviewed, he then posed another question: “So what?” He emphasized that our Industry needs to rethink how we approach weed control. We tend to have unrealistic expectations for our weed control programs, manage with short term thinking – “see the weed, kill the weed,” and use tunnel vision control solutions. We never follow up and ask why we have the weed in the first place. Our emphasis should be “predict & prevent” and we should take a multi-year systemic approach.

Reid suggested an alternative strategy to managing weeds. First, we need to circle back to the first principal of IWM – identification. What weeds are we dealing with? Do we understand their unique biology? Do we understand what is acceptable control and why? How do we accomplish that? The expectation is that we will kill the perennial weed at the correct stage in the life cycle and eliminate them prior to the place in the rotation where we can’t effectively control them. The Modes of Actions (MOAs) should be rotated across the whole rotation to save the critical ones (Grp 14), for the crop with the fewest/poorest options (soybeans). The evaluation component of IWM is an ongoing process where we need to determine what is working, what is not working, and how do we change the system for the better.

In terms of herbicide tolerant weeds, Reid believes that we can better manage weeds and delay how much resistance affects us indefinitely if we are proactive. Typically, Ontario has longer, more diverse rotations than the rest of the corn belt. We also still have perennial crops in our landscapes, hay and pastures, that can allow us to break up that 2-3 year rotational cropping system. Acknowledging where we are today, he suggested that we need to diversify our cropping systems even further, to include crops like edible beans, oats, sunflowers,and canola.

Craig Reid in Field

Craig Reid inspecting the field

With climate change, we should anticipate more weeds moving into midwestern Ontario. We must also concede that no one method of control is foolproof. Often, IPM principles are at odds with one another for different pest species. For example, tillage can be a fantastic way to deter northern corn leaf blight, but it makes white mold worse, and it has negative impacts when it comes to soil health. Sometimes we are working against ourselves and picking the lesser of two evils.

Reid concluded with a quote from Sun Tzu, The Art of War. “If you know the enemy and know yourself, you need not fear the result of a hundred battles. If you know yourself but not the enemy, for every victory gained you will also suffer a defeat. If you know neither the enemy nor yourself, you will succumb in every battle.” It does not go unnoticed that he finished this presentation about weed control with a war/battle metaphor. Point taken.

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