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Stem Minning Weevils

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In the spring of 2016 there was interest from the GWFA projects committee and board in trying out different biological control agents for weed control. After some research and discussion with other Forage and Applied Research Associations, GWFA decided to develop a couple of projects to test weevil success. GWFA reached out to its membership and its partners to see if there would be any interest in partnering on a project with the Canada Thistle Stem Mining Weevil.

Through the summer GWFA staff developed two different projects and protocols for running the trials. The first is the Monitoring Project. It is a set area of about four meters by four meters. Thistle stand counts were done to determine an approximate population within the test area. Then one cup of weevils would be released into the center of the test area. A cup of weevils contains 105 weevils.

Since the weevils are released in the fall there wouldn’t be any reproduction occurring in the fall only burrowing of the adults into the soil. The following summer thistle dissections would be completed at random to determine if the weevils are reproducing by larvae presence and get an approximate population.

In year three and on, we would do plant stand counts and thistle dissections to determine if we are seeing a reduction is thistle population and a growth in the weevil’s population. This will be a long-term project and we hope to maintain our locations for at least a five-year period. GWFA has partnered with Lacombe County, Medicine River Watershed Society, and County of Wetaskiwin in this style of project.

GWFA is managing the local locations and County of Wetaskiwin is using our protocols to run their own project, but will be providing us with the data they collect.

The second project we developed protocols for, is a longer term multi test location project. We would like to see if there is any benefit to ‘overloading’ a thistle population initially to speed up control and what would be a release rate that would increase the rate of control without being cost prohibitive. We will have 4 tests, a check with no weevils, a single release, a two-cup release, and finally a three-cup release. These sites will be separated, but will need to represent similar climates, topographies, and land use. The size of the test sites is the same as the monitoring project. Currently we have commitment to two locations of this magnitude with Mountain View County. The sites will be selected in spring of 2017 and the initial setup will be done during the summer and the release will follow in the fall.

Unfortunately, we were unable to do any weevil release in the fall of 2016. There was a freak weather event right before the weevils were to be picked up in Montana. The early snow caused the weevils to go underground earlier than normal and could not be collected.  We will be doing the releases on all our locations in 2017.

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