In May of 2025, staff from the Huerfano County Noxious Weed Department and Biological Control Specialists from the Colorado Department of Agriculture released the newly approved biological control Aceria drabae along Wahatoya Creek, east of La Veta. Originating from Europe and Central Asia, this microscopic gall mite targets only hoary cress (aka whitetop), which is a Colorado State Class B noxious plant species. Initially introduced in the United States in 2019, Huerfano County Government is among the first entities in Colorado to have the opportunity to utilize this new biological control. Previously no approved biological control was available for white top, due in part to its close taxonomy with other desirable species in the Brassicas family like broccoli, cabbage and cauliflower. This close taxonomical relationship had been a major hurdle towards establishing a host specific biological control for white top given the high risk of causing off target damage to the aforementioned desirable members of the Brassicas family. Thankfully, after literally decades of research, the Federal entity known as APHIS (Animal & Plant Health Inspection Service) determined that the miniscule Aceria drabae mite was host specific to white top and did not pose a risk to desirable commodities, thereby opening the door for initial releases to take place in 2019 within Montana and Wyoming. Upon the successful establishment of Aceria drabae in these states, the Colorado Department of Agriculture’s Palisade Insectary coordinated with the State of Montana so that they could secure infected plant material for releases in Colorado.
Fast forward to the time of this writing in autumn of 2025, Huerfano County staff have had the opportunity to revisit the May release site and are happy to report that a population of Aceria drabae has been successfully established at the Wahatoya Creek site, as evidenced by the malformed and discolored seedlings\rosettes. With the establishment of this new biological control in Huerfano, it is the fourth exotic biological control established within our county within the last six years. Assuming this population survives the upcoming long winter months, it will prove to be an invaluable tool in our arsenal towards the control of white top within our jurisdiction. Being an aggressive perennial species that reproduces by seed and its extensive rhizomatous root system, white top has infested over 2,000 acres in Huerfano County since its introduction to the state over a century ago. While this biological control will not totally kill the host plant, it drastically reduces seed production and root development, creating a vital natural check and balance similar to those found in its native range where it is not invasive as it is here in the New World. Infected plants display stunted shoot growth and gall formation, with multiple generations of the mite reproducing in a single season. Given their small size, the mites are transported throughout the environment upon the winds and bodies of other insects. Huerfano County staff chose the Wahatoya Creek site due to the heavy concentrations of white top that are present within the surrounding countryside, being most apparent during the spring and early summer months. For small, understaffed entities like Huerfano County, biological controls prove to be an exceptional force multiplier; providing borderless control and reduced herbicide usage. As this particular control program develops, Huerfano County staff will continue to monitor and facilitate the spread of Aceria drabae within our area and coordinate with affected landowners so that a large scale control effort can be realized. As field duties subside with the onset of winter, department staff will be hosting a series of presentations that will further explore this and other noxious weed control options for Huerfano County landowners. Stay tuned for more information.
