Ecological Weed ManagementEPM7

Integrated Control of Musk Thistle Integrated Control of Musk Thistle using an Introduced Weevil.using an Introduced Weevil.

Richard C. McDonald, Ph.D.Richard C. McDonald, Ph.D.

Musk Thistle - Carduus nutans L.

Introduced into the eastern seaboard in mid-Introduced into the eastern seaboard in mid-1800s from Europe as ship’s ballast1800s from Europe as ship’s ballast

Quickly spread east; seeds are windborneQuickly spread east; seeds are windborne Missouri - 1st detected in 1940sMissouri - 1st detected in 1940s By mid-70s, major noxious weed problemBy mid-70s, major noxious weed problem Chemical control of all areas not feasibleChemical 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

1973 - 1 in 10 counties 1973 - 1 in 10 counties in US had economic in US had economic infestations of MT.infestations of MT.

1 MT plant per 1.5 m 1 MT plant per 1.5 m reduced pasture yields reduced pasture yields by 23%by 23%

Outcompetes NativesOutcompetes Natives Declared noxious Declared noxious

weed-law 1981 in MOweed-law 1981 in MO

EPM of Musk Thistle

Controls: spraying, Controls: spraying, digging, mowing.digging, mowing.

Controls were not very Controls were not very cost effectivecost effective

Many farmers and Many farmers and dairymen were going dairymen were going broke.broke.

Land value decreased Land value decreased more than $100/acre more than $100/acre because of thistles.because of thistles.

EPM of Musk Thistle

Nationally, MT was Nationally, MT was causing tremendous causing tremendous problemsproblems

Tordon-herbicide-Tordon-herbicide-contaminating water contaminating water and killing cattleand killing cattle

MT seemed to be out MT seemed to be out of control.of control.

EPM of Musk Thistle

In Missouri, MT was In Missouri, MT was costing at least $5 costing at least $5 million in lost forage million in lost forage yearly since the 60s.yearly since the 60s.

Landowners/Hwy Landowners/Hwy Depts - $+1 million on Depts - $+1 million on herbicidesherbicides

Totals: $6 million and Totals: $6 million and $126 million/year$126 million/year

EPM of Musk Thistle

USDA researchers in USDA researchers in Eurasia - why MT Eurasia - why MT wasn’t a problem therewasn’t a problem there

Insects/diseases that Insects/diseases that limited the ability of limited the ability of MT to reproduceMT to reproduce

Musk Thistle weevilMusk Thistle weevilRhinocyllus conicusRhinocyllus conicus

FroelichFroelich

EPM of Musk Thistle

EPM of Musk Thistle

M.S. - Distribution and Impact of R. M.S. - Distribution and Impact of R. conicus in Missouri (1982)conicus in Missouri (1982)

Determined types/amounts of controls usedDetermined types/amounts of controls used Visited 99 release sites - thistle density, Visited 99 release sites - thistle density,

weevil density, and seed productionweevil density, and seed production Impact of weevil on thistle populations over Impact of weevil on thistle populations over

a total of 5 to 7 year period.a total of 5 to 7 year period.

EPM of Musk Thistle

At each site - sample At each site - sample EPM formEPM form

Recorded thistle Recorded thistle density, density, presence/absence of presence/absence of weevil, samples of weevil, samples of terminal and lateral terminal and lateral flowerheads to flowerheads to determine seed determine seed productionproduction

EPM of Musk Thistle

EPM of Musk Thistle

EPM of Musk Thistle-Findings

1 million acres infested in Missouri1 million acres infested in Missouri $1 million in herbicides; most controls were $1 million in herbicides; most controls were

applied incorrectlyapplied incorrectly Musk Thistle weevil caused a 70-95% reduction in Musk Thistle weevil caused a 70-95% reduction in

thistles with EPM - rotational grazing, pasture thistles with EPM - rotational grazing, pasture management and focus on biological controlmanagement and focus on biological control

Increase establishment and efficacy of weevilsIncrease establishment and efficacy of weevils Published Guidesheet with findingsPublished Guidesheet with findings

EPM of Musk Thistle

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EPM of Musk Thistle

EPM of Musk Thistle

q - level of suppression by weevilq - level of suppression by weevil q= new equilibrium population/prior q= new equilibrium population/prior

equilibrium positionequilibrium position q= 109/1936 = 0.05q= 109/1936 = 0.05 In our study plots, data showed a 95% In our study plots, data showed a 95%

reduction in thistle density with no other reduction in thistle density with no other controls applied.controls applied.

EPM of Musk Thistle

Graph of MT Graph of MT population density at population density at initial release siteinitial release site

Graph of weevil Graph of weevil densities per head at densities per head at original release siteoriginal release site

EPM of Musk Thistle

MT biocontrol program caused a 70% to MT biocontrol program caused a 70% to 95% reduction in musk thistle density after 95% reduction in musk thistle density after 5-7 years.5-7 years.

Resulted in an annual savings of $6 to $126 Resulted in an annual savings of $6 to $126 million dollars in increased land value and million dollars in increased land value and reduced use of herbicides, especially reduced use of herbicides, especially Tordon and 2,4-D.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 We were able to increase collections, releases and collections, releases and establishment rates for the establishment rates for the MT flowerhead weevil.MT flowerhead weevil.

Sustainable suppression of Sustainable suppression of thistles; Missouri does not thistles; Missouri does not have economic levels of have economic levels of thistles now.thistles now.

We were able to Integrate We were able to Integrate control methods to control methods to suppress thistles and suppress thistles and protect weevils.protect weevils.