State seeks solution for cheatgrass infestation

Wild Horse Island is a natural gem, known for its bighorn sheep, bald eagles and wild horses.

But a few unwelcome guests have also found their way onto the island and one, in particular, is making its mark on the landscape: cheatgrass.

This invasive winter grass inhabits an estimated 100 million acres across the U.S., destroying soils and edging out native vegetation acre by acre. It’s hardy, adaptable and difficult to eradicate. While most plants sprout in the spring, cheatgrass’ germination begins in the fall, giving it a head start over other flora. In addition to its prolific seed production — each plant can produce hundreds — cheatgrass has a shallow root network, allowing it to suck up water before it reaches the deeper roots of other vegetation.

Montana Fish, Wildlife and Parks is currently testing a potential solution to this pervasive problem — a micronutrient fertilizer developed by geologist and land reclamation scientist Stuart Jennings of Bozeman. The fertilizer isn’t commercially available yet, but is being tested on Wild Horse Island and other locations throughout the West to determine the most effective dosage and when best to apply it.

Traditionally, cheatgrass has been managed by applying herbicides to the grass when it germinates in the fall. However, since it’s such a prolific seed producer, by springtime cheatgrass often returns. Jennings’ approach is aimed at blocking cheatgrass growth from the start by altering the soil chemistry to favor more desirable native plants.

“What I’m trying to do is restore soil health by giving it back the building blocks for soils to defend themselves against weedy invaders,” Jennings explained. “As it turns out, the weedy species don’t like micronutrient fertilizers … the main thing that’s innovating about this is it actually works and it’s nonsynthetic.”

To determine the effectiveness of Jennings’ fertilizer, FWP staff applied the mixture in September 2018. They spread the fertilizer in different doses on three sites on the island with varying levels of cheatgrass infestation.

Montana Fish, Wildlife and Parks Wildlife Biologist Franz Ingelfinger said there has been “decent success” in some early experiments with the fertilizer, which inhibits the germination of cheatgrass.

Jennings is more enthusiastic about the results.

The “weediest site,” located on a former homestead area, saw a significant reduction in cheatgrass coverage — it was measured at 90 percent in the fall and fell to 5 to 10 percent by June, Jennings said. The location with medium levels of cheatgrass infestation saw a drop from 20 percent coverage before fertilizer application to “right around 5 percent.”

“We didn’t get rid of every plant, but we made a big step in the right direction,” Jennings said.

However, only time will tell how effective the method proves on the island. Ingelfinger estimates that it will be 3 to 5 years before the department will have a conclusive answer. They want to examine how long-lasting the effects of the fertilizer are and how the substance impacts other vegetation, especially desirable plants, over time.

“[Cheatgrass] has been a big issue for a long time. It’s one that we’re challenged to manage,” Ingelfinger said. “I’m constantly looking for approaches that are scalable and sustainable and also critical of ones that aren’t … We’ll see what the data tells us and go from there — it’s not something that a single growing season or two is going to tell us.”

If the fertilizer does prove effective at reducing cheatgrass on the island, it could mean an increase in native plants and grasses — the preferred diet of the island’s animal inhabitants.

“[Cheatgrass] isn’t necessarily bad for them, but what it does tend to do is out-compete plants that are better for them,” FWP Park Management Specialist David Landstrom said. “The native plant communities on the open part of the park …..that’s what’s been so useful to sheep and deer and horses on the island.”

Optimizing the health of the island wildlife is integral to the mission of the Wild Sheep Foundation, which, along with the Montana Wild Sheep Foundation, partnered with the state park by providing financial support for the study. Wild Horse Island is an important source for transplant bighorn sheep — sheep that are relocated from the island to bolster herds in other locations throughout the state and western region.

Wild Sheep Foundation Conservation Director Kurt Alt connected the state agency with Jennings after learning of his other fertilizer tests in the Butte and Bozeman areas.

“Cheatgrass is ubiquitous throughout the West. It has become dominant on degraded rangelands and is difficult to control,” Alt wrote in an email. “We felt the importance of this project and its potential application throughout the West for both wildlife and agriculture could be one of the most important habitat enhancement projects we could undertake in the west.”

Landstrom said he hopes the fertilizer will be a cost-effective method to reduce the spread of cheatgrass and one that can be applied despite the logistical challenges the island provides. Not only is Wild Horse miles off the main shoreline, there are aren’t any roads to transport large equipment, making traditional application methods challenging.

“There’s so much of it and it’s in such a remote location that doing with backpack sprayer like we do now, there’s no way we could make a dent,” Landstorm said. “There’s not a whole lot of effective treatments out there. This is an attempt to find an effective way to deal with it and a more affordable means.”

Reporter Mackenzie Reiss can be reached at mreiss@dailyinterlake.com or (406) 758-4433.