The Hidden Threat

What a threat a herbicide-resistant weed would be in Montana wheat! This is one of five U.S. states that grow half the country’s entire wheat crop. And if the million inhabitants of Montana had to eat all the wheat they raise, every man, woman and child would have to consume 400 loaves a day! Gordon Stoner farms 12,000 acres near Outlook in Sheridan County in the northeast part of the state. Stoner Farms is a 100% no-till, continuous cropping operations raising durum wheat, peas, corn, oil seeds and lentils along with a commercial cow/calf operation. After gaining a business degree, Gordon returned to the family farm in 1980, first converted to no-till in 1990, and went 100% no-till in 2000.

Resistance on the horizon

Sheridan County has a semi-arid climate with only 10-12” annual precipitation and ground frost for five months of the year, and “it’s only the frost that enables us to grow crops at all,” Gordon says. Up to fall 2015, Gordon could safely say there was no documented weed resistance on his farm, though he had spotted some yellow foxtail in his wheat following a pea or lentil crop. But some of his fellow-farmers had a different story to tell. Tight rotations are common in Sheridan County – “wheat, lentils, wheat, lentils, wheat, lentils …”, as Gordon says – and those farmers “already have a real resistance problem. And as we have resistance in our county, I’m sure going to be facing problems soon.”

How Gordon keeps resistance at bay

As yet, sensible weed management practices have kept Gordon’s fields resistance-free. Besides always applying herbicides at their maximum labeled rates, Gordon rotates his herbicides to ensure multiple modes of action are deployed, practices diverse crop rotation, applies plenty of late-season herbicides to kill off weeds before the long winter, and uses the latest application technology, e.g. nozzle-by-nozzle control to ensure uniform herbicide placement. Yet despite this, Gordon is aware how close the  hidden threat is to becoming a real issue. The harsh Montana climate doesn’t help.

No more cover crops

After experimenting for five years, Gordon has given up on cover crops: “The growing season is just too short and water too precious.” Residual herbicides have damaged succeeding crops, with recommended plant-back periods proving inaccurate in drought conditions. From 1 November 2014 to 1 September 2015 only 3½ inches of precipitation fell on his farmland. Soil-active herbicides also fail in such dry conditions and more exotic multiple herbicide tank mixes have proven too stressful. One neighbor’s crop stopped growing at 6” after such a mix.

Diversity is key

So what are Gordon’s future plans? Besides exploring additional crop rotations, e.g. sorghum, and using additional tank-mix partners, he is “waiting for the next new mode of action” but knows it could be a few years in coming. Till then, he’ll carry on with his diverse weed management practices so resistance stays away as long as possible.