Ecological Weed Management EPM7 Integrated Control of Musk Thistle using an Introduced Weevil. Richard C. McDonald, Ph.D.

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

Musk Thistle Stages

EPM of Musk Thistle 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

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.

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

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

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

EPM of Musk Thistle

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

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

EPM of Musk Thistle

EPM of Musk Thistle-Findings 1 million acres infested in Missouri 1 million acres infested in Missouri $1 million in herbicides; most controls were applied incorrectly $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 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 Increase establishment and efficacy of weevils Published Guidesheet with findings Published Guidesheet with findings

EPM of Musk Thistle

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

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

EPM of Musk Thistle MT biocontrol program caused a 70% to 95% reduction in musk thistle density after 5-7 years. 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. 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! Program was run on $3000/year!

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.