How a tiny mite could slow the spread of whitetop throughout the state

What some people may think is a beautiful white flower is actually an aggressively invasive weed. Hoary cress, also known as whitetop, is a noxious weed that causes many problems throughout Wyoming. To mitigate the spread of this noxious weed, the Wyoming Weed and Pest Council (WWPC) has begun biological control with a tiny mite.

Whitetop is a highly invasive and state-designated noxious weed. Originally native to the Mediterranean and areas of Asia, whitetop stops the growth of nearby plant species, which reduces native biodiversity, crop yields and more. It also is indigestible and toxic to livestock.

This weed completely takes over and impacts recreation, irrigation, farming and the economy. It costs millions of dollars to control it, and the costs increase due to inflation and economic downturn.

“Whitetop has affected every single county in Wyoming for a long time,” said Larry Smith, President of Wyoming Weed and Pest Council. “While we’re dedicated to managing and controlling the spread of this invasive weed, it is difficult to contain. We implement cultural practices, herbicides and grazing every year to slow the spread, but it still heavily impacts Wyoming. That’s why we need biological control to help over time.”

Because of the severe repercussions whitetop has had on Wyoming, WWPC has been contributing to biological control research about hoary cress since 2001. After years of research and development, the first whitetop biological control agent was approved for release in the U.S. This project was a joint effort between Montana State University and the USDA Agricultural Research Service - European Biological Control Laboratory.

Researchers found that a tiny, plant-feeding gall mite, Aceria drabae, can feed and develop on whitetop without threatening native plants and wildlife. These mites, originally from northern Greece, are incredibly small - nearly invisible to the naked eye. They are dispersed on the invasive weed by the wind.

The mite harms whitetop plants by causing a “gall.” Galls are abnormal growths that can develop primarily on plants’ flowers, flower buds and sometimes the stems. Usually, they grow in reaction to the mites feeding on the plant. Galls divert energy from the plant, preventing the formation of seeds and potentially stunting growth.

After over two decades, Wyoming can finally start releasing the mite in Fremont County. This project will take time and isn’t expected to eradicate whitetop in Wyoming. As the mites’ population grows, the weed’s seed production will be limited. It won’t be able to spread as quickly. And since it is just starting, the species will need to be tested more over time. Hopefully, this project will help save thousands of dollars and improve invasive species control.

“This biocontrol agent won’t be the cure of whitetop, but we are excited to have another tool in our toolbox,” said Aaron Foster, Chairman of the Wyoming Biological Control Steering Committee. “We hope once the mites are established in Fremont County, we’ll be able to share with other counties and eventually have it everywhere in the state.”

To learn more about this biological control project and others throughout Wyoming, visit Wyoming Weed and Pest Biological Control. For more information about Wyoming Weed and Pest Council, visit wyoweed.org and follow on Facebook and Twitter.

About the Wyoming Weed and Pest Council

Wyoming Weed and Pest Council (WWPC) is comprised of 23 Weed and Pest Districts in the state of Wyoming. The Council works closely with the Wyoming Department of Agriculture and the University of Wyoming to keep current with the latest technology and research available in the ongoing management of noxious weeds and pests. The overall mission is to provide unified support and leadership for integrated management of noxious weeds and pests to protect economic and ecological resources in the state.