Non-native invasive species have the potential to cause various problems in small
isolated ecosystems, these constraints are exemplified in the small, shallow, lakes of
Minnesota. Curlyleaf pondweed (Potamogeton crispus L.) is one of the common
occurring and most influential non-native invasive species in Minnesota. Characterized
by its early spring growth and early summer senescence, curlyleaf has the ability to
negatively affect native macrophyte growth by forming dense monotypic canopies in late
spring and releasing nutrients in early summer. Because of the negative impact on natural
ecosystems along with the problems curlyleaf can cause for people, there is serious
interest in the management of curlyleaf. One management practice is the early season
application of herbicides, where curlyleaf is targeted before it is capable of producing
turions (propagules) and native plants are unlikely to be affected.
We examined the response of native plant communities to spring herbicide
treatments of curlyleaf pondweed from 2006 through 2009. Thirteen lakes were
examined during our study; ten were treated with herbicide and three were used as nontreatment
reference lakes. Plant communities were assessed in the littoral zone with the
point intercept method in early spring (before treatment), late spring (after treatment) and
mid summer (peak native plant growth). For each survey, approximately 40 random
biomass samples were taken in each study lake to estimate plant biomass. To determine
changes in native plant frequency and biomass throughout the course of consecutive
annual treatments, we compared differences between treated and untreated lakes within
years for August surveys and compared August surveys between years for treated or
untreated lakes. Additionally, we examined inter-seasonal changes, comparing differences within and between treated or untreated lakes from May to June and June to
August in every year.
In the reference lakes, curlyleaf persisted at moderate to high frequencies over the
four years, and no consistent changes in native plant frequencies were seen. Herbicide
treatments proved effective for controlling curlyleaf, which decreased in frequency
within 1 month following treatment for each year of the study. The total frequency of
occurrence of native plants in August did not decrease in most of the treatment lakes
between years. Native macrophyte species richness also showed little change with
continued treatment, although shifts in abundance of some species were observed. August
native plant biomass increased between 2006 and 2009 in most treatment lakes, whereas
native biomass varied in untreated lakes. Much of the change in biomass was attributed to
a single species in most treatment lakes. We observed increases of Chara spp. frequency
and biomass in most treated lakes. However, multiple years of treatment may be needed
to obtain increases in native plant abundance as the largest increases occurred after 3
years of treatment. Early-season lake-wide herbicidal treatments of curlyleaf pondweed
can reduce curlyleaf occurrence and density without major harm to native plants.
Significant inter-seasonal changes in frequency and biomass were observed in
both treated and untreated lakes although differences were not observed between treated
and untreated lakes. Native species richness increased from May to June and June to
August in both treated and untreated lakes. The frequency of native plants increased
between May and June but less so between June and August in both treated and untreated lakes. Conversely, native plant biomass increased from June to August more so than from
May to June for both treated and untreated lakes. These findings suggest that early season growth primarily manifests in distribution and colonization, while late season growth
results in increased biomass. Similarly, many plant species follow the same patterns as
the overall native plants, although other plant species may have different frequency and
biomass regimes throughout a single season. Despite the differences in native plant
species, we did not see any major inter-seasonal detriment caused by the presence of
curlyleaf pondweed in untreated lakes, or positive influence of herbicide treatment in
treated lakes. These findings suggest that increases in native plant growth may occur only
after several annual treatments.
University of Minnesota M.S. thesis. September 2010. Major: Water resources science. Advisor: Raymond M. Newman. 1 computer file (PDF); ix, 104 pages.
Jones, Ajay Robert.
Effects of repeated early season herbicide treatments of curlyleaf pondweed on native macrophyte assemblages in Minnesota Lakes..
Retrieved from the University of Minnesota Digital Conservancy,
Content distributed via the University of Minnesota's Digital Conservancy may be subject to additional license and use restrictions applied by the depositor.