Most growers are familiar with the term IPM (short for integrated pest management). While it is crucial, pests aren’t the only enemy growers face.
Speaking specifically about diversifying weed management strategies for improving weed control in cole crops – but with a larger message about all weed control – at the most recent Great Lakes Expo was Thierry Besançon, associate Extension specialist in weed science in Rutgers University’s Department of Plant Biology.
The research he discussed was done in cooperation with Lynn Sosnoskie, assistant professor in the School of Integrative Plant Science, Horticulture Section, with Cornell AgriTech.
First and foremost, unmanaged weeds are nothing if not expensive. Crops grown with best management practices but no weed control can see major potential yield losses. Besançon noted a 2018 study that found a 71.4% potential yield loss in dry beans due to weeds, costing up to $722 million a year. A separate overview in 2022 found a 54% yield loss on average throughout 44 studies conducted over 20 years in Michigan, New Jersey, New York and Wisconsin in cabbage.
So Besançon suggested IWM – integrated weed management – in cooperation with IPM. IWM combines multiple methods and practices to manage weeds. The first layer is always prevention, followed by overlapping chemical, biological, cultural and mechanical methods.
“IWM is needed when current chemical strategies are no longer effective; when a new weed species enters a field; and due to the increased societal demand for less pesticides,” Besançon said.
There are already some useful tools in the IWM toolbox. One is proper weed identification. Besançon noted two particular apps – PictureThis and Pl@ntNet – as “the best two we evaluated,” adding that it may be worth downloading both to confirm weed ID.
Proper weed identification helps a grower determine how a species came to a field site – wind-dispersed seeds vs. potential entry on equipment, for example. It also helps to identify areas of the field favorable to weed infestation (like nutsedges in wet places, compacted soil areas and spots with weak crop coverage).
Most importantly, it helps the development of a weed management program based on a projected response to treatment.
Another necessary tool is prevention (such as equipment cleaning and clean seed production). There are cultural practices, like cover cropping, crop rotation, varied planting dates and varied row spacing, to utilize as well.
All the steps taken to prevent the introduction, establishment and spread of a weed species are considered prevention. Weed-free irrigation water; reducing weed seed viability through composting process of natural mulches; preventing seed production on field borders (via mowing or planting boundary strips); and cleaning equipment before moving it from infested to non-infested fields are some strong prevention tactics.
“Never let weeds go to seed,” Besançon warned.
Pay attention to the appropriate rate, timing and placement of fertilizer. “Feed the crop, not the weeds!” Besançon said. And when choosing the crop, variety selection matters. He prefers cultivars that can quickly vine and shade the ground (either through leaf shape, soil shading or vertical growth).
He added that reduced row spacing and increased planting density means more uniform plant distribution across the field. Rotating crops and integrating grass crops is critical to ensure no single weed species dominates the field.
In regards to cover crops, in an ongoing test of clover living mulch with broccoli in New Jersey, Besançon said they saw an 88% decrease in weed pressure. However, it did result in a yield decrease in the broccoli, due to competition for nutrients in water. A silver lining: Red clover does attract beneficial insects to fight cabbage hooper pest.
Then, of course, herbicides are always being updated and formulated, so pay attention to new classes and combinations.
Besançon also briefly mentioned “the future of weed control” with products such as Naïo Oz’s autonomous ag robots and Carbon Robotics’ LaserWeeder™.
The last thing growers need to worry about is another acronym to remember, but IWM is one that seems worth it.
by Courtney Llewellyn
