Biological Control of Garlic Mustard

Biocontrol of Garlic Mustard and Buckthorn,an UpdateJeanie Katovich, Esther Gerber,Hariet Hinz, Luke Skinner, David RagsdaleRoger Becker, Laura Van Riper and AndreGassman

Where is garlic mustard a problem?Garlic mustardis a problem inthe forest understorywhere it can crowdout more desirablenative speciesSteve Katovich

Garlic mustard is also a problem alongforest edges and pathways

Garlic mustard distribution by state

Garlic mustard is a biennial plantBeckerGarlic mustard seedlingsemerge early In the spring

Garlic mustard grows as a rosette duringthe first year.Steve Katovich

In the spring of thesecond season,garlic mustardrosettes bolt andflower.

Garlic mustard flowerBecker

Garlic mustardplants form seedcapsules in earlysummer

Seeds mature by mid-July

Mature garlic mustard seedsBecker

Potential Garlic MustardBiocontrol Insects

Potential Biocontrol Insects forGarlic Mustard• Ceutorhynchus scrobicollis - crown miner• Ceutorhynchus roberti – stem miner• Ceutorhynchus alliariae – stem miner• Ceutorhynchus constrictus – seed feeder

Ceutorhynchus scrobicollisMcCornack

C. scrobicollis Life CycleSummerAdult AestivationSpringSoil pupationAdult emergenceFallOvipositionWinterOviposition andLarval Development

McCornack

Brian McCornack

Brian McCornack

New Lateral GrowthMain Root CrownLarval Damage

Impact of C. scrobicollis ongarlic mustard plants• Increased plant mortality• Reduced above ground biomass• Reduced seed output

Shoot MinersC.alliariae and C. robertiCABI-Bioscience

CABI-Bioscience

Ceutorhynchus scrobicollisC. robertiC. alliariae312..not to forget Ceutorhynchus constrictus..CABI-Bioscience

Host RangeSet of plant species on which abiological control insect can feedand develop (McEvoy, 1996)

The ideal biological weedcontrol insect would onlycomplete its life cycle onthe target weed

High Security Containment FacilityUniversity of Minnesota, St. Paul, MN

Results of Host Range TestingC. scrobicollis• 88 plant species included in nochoicetesting• 51 plant species included in larvaldevelopment tests.

Results of Host Range TestsC. scrobicollis• No plant species outside of the Brassicaceae family wereattacked by C. scrobicollis.• Within the Brassicaceae family, many plant species wereaccepted for oviposition but did not support larvaldevelopment.• In larval development testing, only one native mustardspecies (Rorippa sinuata) supported the development ofadults.• When both garlic mustard and Rorippa sinuata wereincluded in single choice testing, only garlic mustard wasattacked. We believe that under field conditions, the risk ofattack to Rorripa sinuata is very low.

Current Status of Host Range TestingProgam• Petition submitted to the Technical AdvisoryGroup for Biological Control Agents of Weeds(TAG).• At TAG reviewers’ request we have included 10additional native mustards, most native tosouthern California, in host range testing.• Additional testing should be completed thiswinter and the TAG petition will be re-submitted.

Buckthorn• Native to Europe• Forms canopies inforest understory• Impacts– Reduced diversity– Ecosystem function– Reduce regenerationof tree seedlings– Bird nestingCommon buckthorn(Rhamnus cathartica)Glossy buckthorn(Frangula alnus)(Heneghan et al. 2002; Schmidt and Whelan 1999)

Potential for BuckthornBiocontrol• Research initiated in 2001– CABI Switzerland• Looking for biological control agentsspecific to R. cathartica and F. alnus– 7 Rhamnus species native to the US– 5 Frangula species native to the US• 39 specialized arthropods were identified• 10 were studied further• Host-specificity testing 2003-present

5 high-priority species forfurther researchSpecies Feeding guild Field hostsTrichochermes walkeri(Homoptera, Triozidae)Cacopsylla rhamnicola(Homoptera, Psyllidae)Trioza rhamni(Homoptera, Triozidae)Wachtiella krumbholzi(Diptera; Cecidomyiidae)Lasioptera kosarzewskella(Diptera ; Cecidomyiidae)Sap-sucker/leaf gall inducerSap-suckerSap-sucker /pit-gall inducerSeed-feederSeed-feederR. catharticaR. cathartica;occurrence onF. alnus needsto beconfirmedR. catharticaR. catharticaR. catharticaGassman et al. 2008 report toLCCMR

Trichochermes walkeri(Homoptera, Triozidae)sap-sucker/leaf gall inducerPhotos by A. Gassmann

Phytoplasma found inT. walkeri• Phytoplasma ‘CandidatusPhytoplasma rhamni’(buckthorn witches’ broom)has been detected in twopopulations of T. walkeri inSwitzerland.• T. walkeri is the first insecthost record for thisphytoplasma.• Need additional studies• Is the phytoplasma in theUS?Photos of other witches broom/ yellows phytoplamsasPhotos from http://en.wikipedia.org/wiki/Phytoplasma

Cacopsylla rhamnicola(Homoptera, Psyllidae)sap-suckerPhotos by A. Gassmann

Gall midgesPhotos by A. Gassmann

Current status of biocontrol• Continue to perform host-specificity tests onpotential biocontrol agents• Challenges– Obtaining and growing native Rhamnus and Frangula– Need insects with specificity and high damage levels• Frangula alnus (glossy buckthorn)– Difficulty finding host-specific insect species– Difficult to grow F. alnus at CABI– Work is now focused on Rhamnus cathartica

Current status of biocontrol• Rhamnus cathartica (common buckthorn)• Consultation with outside experts will direct work in2010-2012• Continue to assess the feasibility of using T. walkeri,C. rhamnicolla, and W. krumbholzi as biologicalcontrol agents for R. cathartica.• Study the causes of the high levels of seed andseedling mortality of R. cathartica observed in Europeas a step toward identifying additional potentialbiological control agents including pathogens.

We would like to thank thefollowing for funding theseprojects:• USDA Forest Service• Minnesota Department of NaturalResources• Legislative-Citizen Commission onMinnesota Resources

Letters of support for garlic mustardbiocontrol projectPlease contact Jeanie Katovich(katov002@umn.edu)