Ecological Weed Management EPM13

1. Ecological Weed ManagementEPM13 Integrated Control of Musk Thistle using an Introduced Weevil. Richard C. McDonald, Ph.D.

2. Musk Thistle - Carduus nutans L. • Introduced into the eastern seaboard in mid-1800s from Europe as ship’s ballast • Quickly spread east; seeds are windborne • Missouri - 1st detected in 1940s • By mid-70s, major noxious weed problem • Chemical control of all areas not feasible • 2,4-D and Tordon were herbicides used.

3. Musk Thistle Stages

4. EPM of Musk Thistle • 1973 - 1 in 10 counties in US had economic infestations of MT. • 1 MT plant per 1.5 m reduced pasture yields by 23% • Outcompetes Natives • Declared noxious weed-law 1981 in MO

5. EPM of Musk Thistle • Controls: spraying, digging, mowing. • Controls were not very cost effective • Many farmers and dairymen were going broke. • Land value decreased more than $100/acre because of thistles.

6. EPM of Musk Thistle • Nationally, MT was causing tremendous problems • Tordon-herbicide-contaminating water and killing cattle • MT seemed to be out of control.

7. EPM of Musk Thistle • In Missouri, MT was costing at least $5 million in lost forage yearly since the 60s. • Landowners/Hwy Depts - $+1 million on herbicides • Totals: $6 million and $126 million/year

8. EPM of Musk Thistle • USDA researchers in Eurasia - why MT wasn’t a problem there • Insects/diseases that limited the ability of MT to reproduce • Musk Thistle weevil Rhinocyllus conicus Froelich

9. EPM of Musk Thistle

10. EPM of Musk Thistle • M.S. - Distribution and Impact of R. conicus in Missouri (1982) • Determined types/amounts of controls used • Visited 99 release sites - thistle density, weevil density, and seed production • Impact of weevil on thistle populations over a total of 5 to 7 year period.

11. EPM of Musk Thistle • At each site - sample EPM form • Recorded thistle density, presence/absence of weevil, samples of terminal and lateral flowerheads to determine seed production

12. EPM of Musk Thistle

13. EPM of Musk Thistle

14. EPM of Musk Thistle-Findings • 1 million acres infested in Missouri • $1 million in herbicides; most controls were applied incorrectly • Musk Thistle weevil caused a 70-95% reduction in thistles with EPM - rotational grazing, pasture management and focus on biological control • Increase establishment and efficacy of weevils • Published Guidesheet with findings

15. EPM of Musk Thistle

16. EPM of Musk Thistle

17. EPM of Musk Thistle • q - level of suppression by weevil • q= new equilibrium population/prior equilibrium position • q= 109/1936 = 0.05 • In our study plots, data showed a 95% reduction in thistle density with no other controls applied.

18. EPM of Musk Thistle • Graph of MT population density at initial release site • Graph of weevil densities per head at original release site

19. EPM of Musk Thistle • MT biocontrol program caused a 70% to 95% reduction in musk thistle density after 5-7 years. • Resulted in an annual savings of $6 to $126 million dollars in increased land value and reduced use of herbicides, especially Tordon and 2,4-D. • Program was run on $3000/year!

20. EPM of Musk Thistle • We were able to increase collections, releases and establishment rates for the MT flowerhead weevil. • Sustainable suppression of thistles; Missouri does not have economic levels of thistles now. • We were able to Integrate control methods to suppress thistles and protect weevils.