Knapweed Biocontrol Collection Field Day
On July 22nd, the Squarrose CWMA hosted a biocontrol collection field day for the knapweed seed head weevil, Larinus minutus. This collection field day was much different than our typical collection field day. We usually invite over 40 cooperators from 10 counties to gather on a single field day. We decided that it was important to continue to collect biocontrol agents for knapweed even during COVID-19 restrictions.
We invited a small group of selected cooperators. In order to maintain social distancing, we set up additional aspirating stations to allow cooperators to space out 6 feet apart. Tools and supplies were assigned to each person at the beginning of the day and cleaned with ammonia throughout the day.
Regional Cooperation
We were able to distribute seed head weevils to seven counties. We were also able to ship our surplus of seed head weevils to cooperators in Washington State. In return, cooperators from Washington sent us the greater seed head weevil, Larinus obtusus, for use on spotted knapweed. The greater seed head weevils were taken to Weber, Box Elder and Cache and Davis Counties. This is a great example of regional cooperation in biocontrol.
Monitoring
As part of our field collection day, we also conducted some on site SIMP analysis on 2 release sites in Juab County.
Tintic Cage Site
The Tintic Cage Site is a challenging monitoring plot to read. Squarrose knapweed is a long lived perennial plant. Even when plants are being damaged by multiple biocontrol agents, the shrubby knapweed will remain for a long time.
We have observed rosette growth at the cage site. Although we have not taken measurable data, we can say that there are less Squarrose knapweed rosettes at the cage site than other areas. Many factors can affect rosette growth. One of the most likely factors is the presence of seed head weevils. Seed head weevil population has increased in 2020. It will be time to conduct some additional root monitoring in 2021 to confirm the presence of both root feeding insects, Cyphocleonus achates and Sphenoptera jugoslavica.
Test Plot Site
The Squarrose knapweed plant population has reduced at the test plot site. The biocontrol transect is not treated with herbicide. However, nearby Squarrose knapweed is being treated. It is possible that the herbicide treatment has an impact on the total seed production in the area. But it is also likely that biocontrol agents have an impact on the Squarrose knapweed at the test plot site. We did see an increase in seed head weevils at the test plot site. It appears that knapweed seed head weevils had a very productive year in 2020.
Special thanks to:
- Juab County Weed Department for assisting in our collection day.
- Tooele County Weed Department for assisting in the collection day.
- Wasatch County for their help at our collection day.
- Box Elder County for their help at our collection day.
- Washing State University for their cooperation in trading biocontrol agents.
