Developing and evaluating new techniques to selectively control invasive plants

Project manager: Ray Newman

Phase I Description: To improve approaches to selectively control invasive aquatic plants such as curly-leaf pondweed with integrated approaches including herbicides, we will work with the DNR to evaluate extant and new strategies to control submersed invasive plants selectively in ways that will also restore native plant communities. We will focus efforts on reanalysis and meta-analysis of data previously collected by the university, the DNR and other cooperators on the effects of curlyleaf pondweed herbicide treatments, including any data collected on the longer-term response after treatments are stopped.

To assess the potential to enhance biological control of Eurasian watermilfoil, enclosure experiments will be conducted to determine if sunfish limit herbivore abundance and control of milfoil.  Previous research has shown that weevils can control water milfoil if sunfish do not consume the weevils. To determine the extent of sunfish consumption of herbivores and factors limiting herbivore abundance in lakes, twenty or more lakes will be surveyed for milfoil, herbivores and sunfish. Sunfish gut contents will be assessed in a subset of these lakes. Analysis of these data will then be used to propose further study.

Project start date: 2013

Estimated project end date: 2016


Enclosure experiments were conducted at Cedar Lake and Peltier Lake in the summer of 2016. Enclosures were installed and stocked with fish; herbivore surveys were conducted and fish diets were collected throughout the summer in Cedar and Peltier as well as other lakes for reference. Upon finding complex and unclear results, this Eurasian watermilfoil biocontrol work is postponed indefinitely.

However, research on curlyleaf pondweed herbicide control is ongoing. Researchers obtained data on curlyleaf pondweed from 67 lakes across Minnesota. This includes pretreatment data and peak curly-leaf pondweed coverage data. This data covered up to ten years of treatments and also included environmental factors such as ice cover and mean snow depth. Preliminary findings include:

  • The number of years treated was a significant predictor of early-season, pre-treatment curly-leaf pondweed frequency and relative abundance, suggesting that repeated treatment with herbicides restricts curly-leaf pondweed distribution and abundance in the spring.
  • More severe winter conditions and repeated herbicide treatment create conditions less favorable for curly-leaf pondweed distribution and growth the following spring.
  • However, overall peak abundance is more influenced by spring growing conditions than prior management or winter conditions.