Washington County Maltese Star-thistle

ISM Monitoring EDRR 2020 Year 1

Introduction

Malta star-thistle (Centaurea melitensis) is a high priority, Class 1A Early Detection Rapid Response (EDRR) species.¹ For EDRR species, it is the goal of the Utah Department of Agriculture and Food (UDAF), to map, monitor, treat, and eradicate the infestation as quickly as possible.  In 2003, two EddMapS points were uploaded near Motoqua showing infestations of Malta star-thistle.  In 2018, the UDAF asked Washington County to re-verify these points. The plants were difficult to find, and were not verified at that time. On April 9, 2020, Brad Winder, the Washington County Weed Supervisor, found about 6-7 acres of plants near La Verkin that he thought could either be yellow star-thistle or Malta star-thistle. He marked the points in EddMapS and reported it to the Utah Weed Supervisor’s Association and UDAF. On April 28, 2020, Corey Ransom, Associate Professor of Weed Science at Utah State University, went out to the site and confirmed that the plant was Malta star-thistle. After the plant was identified, a group effort was made to contain this species. Washington County worked with the Utah Weed Supervisor’s Association and USU Extension to get funding to begin treatment at La Verkin. Several agencies and volunteer groups helped apply for grants, identify and locate more plant populations, and treatment. UDAF helped facilitate the identification of the plant, assisted in the grant application process, and mapped and monitored the sites on June 9-12 as part of its EDRR monitoring protocol. This report is a summary of the first year of monitoring prior to treatment.

Location

UDAF staff, with Brad Winder and Ben Scow from USU Extension, worked in different areas of Washington County to verify and map Malta star-thistle. The plant was typically on road sides. They verified populations on the shoulder and in the median of I-15 near the 20 mile mark (Fig. 2). They verified and mapped a population on SR-9 near the Hurricane Walmart (Fig. 2).  One population was particularly concerning because it is close to Zion National Park in Springdale (Fig. 2). In 2020, Brad Winder and Ben Scow were able to find the 2003 Motoqua points (Fig. 2). UDAF also re-visited the Motoqua points and found that the plants were yellow star-thistle (Centaurea solstitialis) and not Malta star-thistle.  The site will be monitored to ensure it doesn’t spread further. UDAF established its first round of detailed monitoring at a larger population near La Verkin, off SR-9, known as the La Verkin Twist (Fig. 1). This property is owned by SITLA and currently serves as habitat for wildlife and a recreational site. Off-roading and camping occur nearby, and there is a shooting range and military proving grounds across the freeway. Therefore, there are numerous vectors spreading this plant, and disturbance occurring, which increases potential for spread. After UDAF’s trip to this site, Brad Winder found an additional 80-90 acres of Malta star-thistle on BLM land North of the La Verkin Twist near the shooting range (Fig. 2). Although the primary project is at La Verkin Twist, controlling Malta star-thistle is very important on a larger scale because it is an EDRR species, and it is close to spreading into nearby National Parks and National Conservation Areas. With time and increased funding, this project should be able to identify and control more Malta star-thistle populations throughout the county.

Target Weeds

The primary target weed is Malta star-thistle, a Class 1A EDRR species.¹ It is an annual  and reproduces through seeds that typically live about 4 years but can live up to 10. These seeds can grow to plants very rapidly to outcompete other plants for many resources.^2,3 Potential problems caused by Malta star-thistle can include competition with native plants, harming animals or people through its spines, and increasing soil erosion.^2,4 This species is new to the state and is a high priority for immediate control and eradication if possible.

Yellow star-thistle is listed in Utah as a Class 2 Control species that is often confused with Malta starthistle (Table 1).¹ It is a winter annual that reproduces through seeds.⁵ Yellow star-thistle is problematic because it causes “chewing disease” in horses;⁶ it grows in dense stands that outcompetes other beneficial plants;⁷ it can cause injury to humans, livestock, and wild animals, and it can decrease soil moisture.⁷ Yellow star-thistle was the plant that actually occurred at the original Malta star-thistles 2003 EddMapS points near Motoqua.

Treatment

Researchers recommend treating the growing rosettes of Malta and Yellow star-thistle with herbicides in the spring or fall. They still can be treated once they bolt with most herbicides but in higher concentrations. Plants should be treated before they begin to flower. One working paper suggests that post-emergent broadleaf herbicides would work best for Malta star-thistle and minimize effects on grasses.² Another paper for yellow star-thistle suggests that also using a long residual pre-emergent can be good for suppressing germination for these high seed producing plants.⁷

Malta star-thistle at the La Verkin Twist site was sprayed with herbicide by Washington County and an additional crew of 5-8 volunteers from multiple agencies and nonprofit organizations. The spray dates were July 1, 8, and 15 early in the day to avoid the afternoon heat. Spraying in July is past the recommended timeframe for both DuraCor® and Esplanade, which were used. However, drought conditions slowed the growth of Malta starthistle, and along with residual herbicide impacts, the treatment should still be beneficial. A total of 102 man hours was spent to carefully spot spray about 14 acres.

Monitoring Methods

For monitoring this project, UDAF began by focusing on mapping. Personnel double checked the known locations and, in some cases, the area around the known locations. As workers found populations, they marked them in EddMapS. At La Verkin Twist, they began trying to map all populations and do a complete population count. As workers did this, they realized the population was much larger than originally thought. They did a very rough polygon around the populations at the site. Then they installed three 100 ft. transects and took several different measurements along the transects. The ground cover photos were analyzed using SamplePoint, and Excel was used to create means and confidence intervals.

Conclusion

                Malta star-thistle is an EDRR species that has been found and verified in Washington County. Brad Winder did an excellent job of questioning a plant species and requesting verification. Corey Ransom from USU was able to verify the plant in Southern Utah within 19 days. After verification, UDAF responded with monitoring within 42 days (about 1.5 months).  In 2 months after verification (64 days), Brad Winder and the Utah Weed Supervisor Association were able to put together funding, a plan, supplies, and a volunteer crew to begin spraying Malta star-thistle. Not only was this an important find, but also an example of coordination between multiple agencies to respond rapidly to a new invader.

The current average percent cover of Malta star-thistle was low at 3.3%. The treatment, although quickly put into place after the plant was discovered, was administered a little later in the season then is recommended. Residual effects should still prove to be beneficial. New and larger populations have been discovered elsewhere. Therefore, controlling and hopefully eradicating this species will need to continue to be a multiagency effort. Also, as time and treatments occur, the sites should be evaluated for the need to revegetate to prevent future noxious weeds from entering the system, increasing overall ecosystem health, and minimizing erosion.

 

This project report is an excerpt of a complete report prepared by Brittany Duncan, monitoring specialist for the Utah Department of Agriculture and Food. You can download the full report below.