Weather Extremes Give Weeds a Bright Future

Last year’s drought and fire didn’t just set back crop yields, damage land and test communities. The extreme weather may also boost exactly the noxious invaders we don’t want — weeds.

Weeds are tough enemies, typically more adaptable to change than their native counterparts. Both droughts AND floods, for example can help spread them. And in Montana, dry conditions have helped them take root.

“So it looks like a promising future for invasive plants, when you think about things going on globally,” Jane Mangold, a professor of Land Management and Environmental Sciences at Montana State University, said at an ag conference here Feb. 7.

Right now, weeds are costing Montana producers tens of millions of dollars.

It’s hard to see exactly how much, but MSU professors have set out to find some data.

They did a survey recently of affected producers, and the small sample (about 130 owners in 45 Montana counties) reported that they spent about 91 cents (including labor costs) per year per acre on treatment, just for treatment of spotted knapweed and leafy spurge. Add in the value of the forage lost to these two weeds, and the cost per acre comes to about $1.33.

That may not sound like much, and it’s not as high as some previous studies. But with livestock grazing on about 60 million acres in Montana, we’re talking about $80 million just for the impacts of those two weeds. The survey didn’t even take into account other weeds, like Canada thistle. It also left out invasive annual grasses like cheatgrass, which stands to grow more in large sections of central and eastern Montana if we get more dry summers, bringing the plant to a level of nuisance it already has in places like the Great Basin and southern Idaho if it’s not controlled.

Mangold offered her thoughts at the Greater Yellowstone Agricultural Forum, held by Montana Land Reliance. More than 100 people attended, including about a dozen Future Farmers of America and Bozeman state Reps. Zach Brown (a Democrat) and Walt Sales (a Republican).

So what will the future hold, and what will producers do to stop these invasions from growing, further depleting usable forage and increasing fire danger and erosion?

Mangold said these things involve complex relationships in a world with changing climate patterns, increasing carbon dioxide levels and changing land uses. And we have limited data on current problems, and what landowners (especially private landowners) are doing to fight weeds.

“There could be a species down the line that we don’t even have in Montana that we’re worried about 20 years from now that we’re not worried about today,” Mangold said. “There’s a lot of unknowns.”

What is known is that for most of a century, Montana temperatures have risen at a pace of about 0.2 degrees per decade. That’s letting weeds spread further north, and into higher elevations, than they were before.

Precipitation has stayed fairly steady over the long haul; but it’s changing, coming at different times. In 2017, for example, a snowy winter gave way to a dry summer and a major fire year, distressing more than a million acres and creating more opportunity for invasives. Floods, too, help the weeds, depositing fresh soil in new places and spreading seeds.

So Montana producers are responding in ever-changing ways. Most producers use herbicides to fight weeds, and about half use more than one method.

For cheatgrass, the resistance may be in the forms of biocontrol, such as bacteria, mites, fungi or insects that move in to the plants and attack their vigor — not killing or consuming them outright, but weakening their ability to reproduce.

It takes careful science and practice to do it right. Pests need to be administered at the right time in the weed’s life, under the proper conditions of temperature and moisture. Once applied, it could take years before they take effect (assuming they work at all). And to use species in this way can require federal approval which could take years to get.

Then there’s livestock grazing for weed management, and the same creatures which sometimes create a welcome environment for weeds can also help get rid of them.

Grazing management, after all, is the world’s second-oldest profession, MSU Professor Jeff Mosley joked.

The process also involves planning — grazing before herbicide application or spreading the seeds of desirable plants when the weeds are being eaten just before the animals graze.Getting cattle (or sheep or goats) to eat away the bad plants takes some convincing, and researchers have, for example, carefully introduced knapweed into livestock diets, using the same feeding bins the cattle associate with plants they like.

In any case, this approach also may take years to get the full results.

To measure the effectiveness, researchers (or, better yet, their graduate students) examine the cattle excrement for seeds, which pass through but are significantly less viable after making that journey.

“The proof is in the pie,” Mosley said.

To read more, visit PrairiePopulist.org.