Farmers must foster weed seed eaters

Crickets and ground beetles are effective predators, often found in shelterbelts and outer strips of the field

If farmers hear crickets out in their fields they should consider themselves fortunate because that’s the sound of free weed-seed control.

“If you hear the crickets, that means the carabids are out. All of the sounds you hear in the evenings, that’s weed-seed predation,” said Chris Willenborg during his presentation at the Saskatchewan Pulse Growers Pulse and Soybean Agronomy Workshop in Saskatoon.

Willenborg said weed-seed predation is responsible for up to 90 percent of all weed-seed losses.

Weed-seed predators are so effective at managing weed seeds, that some scientists are beginning to re-examine their assumptions on why cover crops are so effective at suppressing weeds.

“There is debate in the weed science world of whether these cover crops are competing with the weeds, or whether that better weed control is a function of increasing habitat for seed predators. That’s how effective they are,” Willenborg said.

Weed-seed predators include earthworms, carabid beetles, invertebrates, voles, mice, rodents and farmland birds such as sparrows and chickadees.

In Western Canada, the most effective weed-seed predators are crickets and grounds beetles.

“For ground beetles, there is a specific type of ground beetle called a carabid beetle. There are about 900 of these species across Canada, 300 of them call the Prairies home and 30 are present in your fields,” Willenborg said.

The amount of seed predation seen on a field depends on the crop.

In corn and soybean fields, there tends to be less seed predation than in smaller grain crops such as wheat or canola. Alfalfa tends to give even better weed-seed predation.

Weed-seed predators can be abundant, but their timing varies based on the time of year.

“Their peak activity is late July through August and declines through early September,” Willenborg said.

Carabid beetles are located on field margins that provide habitat. They also tend to be where the actively growing weeds are located, more so than where weed seeds are on the field, Willenborg said.

This is likely because they tend to go where the seeds will be shed, or because they are seeking cover from their predators.

Studies on how to encourage carabid beetles have been conducted through Penn State College of Agricultural Sciences, and they show diverse crop rotations bolster the carabid beetle activity.

Different types of beetles feed at different times of the year, and the timing of peak seed predation also varies depending on the crop.

So “by incorporation of these diverse crop rotations you are essentially, over a three or four year period, maximizing the different niches these seed predators are occupying so you can maximize the amount of seed predation,” Willenborg said.

Another way to encourage weed-seed predation by beneficial in-sects is by using a beetle bank.

“This is essentially a trap crop or a trap strip usually permanent in nature, some form of broadleaf or grassy strip in the centre of a field that provides habitat. This is be-coming common in Europe,” Willenborg said.

These beetle banks, often seeded every 100 metres, allows beneficials to congregate and overwinter. Shelter belts and field margins serve the same purpose, although many of these areas have been removed in Western Canada and it is unknown how their re-moval has affected seed predators, he said.

Cover crops also help promote weed seed predation by sheltering seed predators.

“These cover crops are providing protection for our seed predators because they are on the menu for many of our different predators, especially birds of prey when it comes to rodents, and farmland birds when it comes to insects.”

Decreasing tillage helps increase seed predators numbers, and multiple studies show seed predator activity is substantially lower on tilled fields.

Willenborg said seed predators require four things: food, water, overwintering habitat and shelter from adversity, and when soil is tilled three of these four things are removed.

“You bury the seeds usually to a depth so that they can’t access them. You remove overwintering habitat because you strip the land bare, there is no shelter.”

Willenborg is working with a graduate student who is looking into how the timing of canopy closure can also affect weed-seed predator activity. They are examining if the wider row spacing now commonly used affects seed predators.

“What we think is happening, by providing a narrow row spacing or a confined spatial arrangement you change the microhabitat…, things like soil moisture, ambient humidity, relative air temperature. All of these things matter to our weed-seed predators,” Willenborg said.

Carabid beetles can significantly benefit crop production beyond eating weed seeds. They also consume many common pests.

Carabid beetles can consume up to their body weight daily, and in doing so can significantly de-crease costs associated with pest control.

For more information on carabid beetles in agriculture, visit 1ZcISUr.

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