Comparison of hybrid and parental watermilfoil growth and phenology in Minnesota Wesley J. Glisson and Daniel Larkin
Eurasian watermilfoil (EWM) Long history of invasion and management Found in North America prior to 1950 Discovered in Lake Minnetonka in 1987
Northern watermilfoil (NWM) Native watermilfoil species Morphologically and genetically similar to Eurasian watermilfoil Moody and Les, 2002
Moody and Les, 2007 Hybrid watermilfoil (HWM) Cross between Eurasian and northern watermilfoil Shares characteristics of both parent species
Hybrid watermilfoil (HWM) Potentially more invasive than EWM, i.e., hybrid vigor Higher growth rates than EWM in lab trials (LaRue et al. 2013) Evidence of herbicide tolerance (LaRue et al. 2013; Berger et al. 2015; Netherland and Willey, 2017) LaRue et al. 2013
Objective Compare the growth and phenology of hybrid watermilfoil (HWM) to its parental species (EWM and NWM) by examining the timing and amount of:
Objective Compare the growth and phenology of hybrid watermilfoil (HWM) to its parental species (EWM and NWM) by examining the timing and amount of: 1. Surface matting
Objective Compare the growth and phenology of hybrid watermilfoil (HWM) to its parental species (EWM and NWM) by examining the timing and amount of: 1. Surface matting 2. Flowering
Objective Compare the growth and phenology of hybrid watermilfoil (HWM) to its parental species (EWM and NWM) by examining the timing and amount of: 1. Surface matting 2. Flowering 3. Stem growth
Study lakes Species Lake County Year(s) EWM Cedar Hennepin 2017-2018 Phalen Ramsey 2017-2018 Auburn Carver 2018 HWM Otter Anoka 2017-2018 Thomas Dakota 2017-2018 Cobblestone Dakota 2018 NWM Big Carnelian Washington 2017-2018 Orchard Dakota 2017-2018 Spectacle Isanti 2018
Sampling methods Surveyed lakes and recorded locations in watermilfoil beds Randomly selected 5 locations for repeated sampling ( 50 m apart) Sampled each location every 2-4 weeks during growing season May November 2017 May present 2018 Sampled each location once during winter January/February 2018
Sampling methods at the surface 5 locations within each lake 5-m radius from boat Surface matting Cover of plants floating at surface Flowers Number of flower heads (inflorescences)
Sampling methods below the surface Novel sampling device Underwater camera with live feed to tablet Camera aimed at a sampling board with 30 cm 70 cm frame 4 samples taken off the side of the boat at each location Counted stems at 0.5 m increments
Results at the surface
Flowers
70 2017 2018 Flowers 60 50 Number of flower heads 40 30 20 10 0 EWM HWM NWM
70 2017 2018 Flowers 60 50 Number of flower heads 40 30 20 10 a a 0 EWM HWM NWM
70 b 2017 2018 Flowers 60 50 Number of flower heads 40 30 20 10 a a 0 EWM HWM NWM
2017 150 HWM EWM NWM 100 Number of flower heads 50 0 Jun Jul Aug Sep Oct Nov Dec
2017 150 HWM EWM NWM 100 Number of flower heads 50 0 Jun Jul Aug Sep Oct Nov Dec
2018 6 HWM EWM 5 NWM 4 Number of flower heads 3 2 1 0 May Jun Jul Aug
2018 250 HWM EWM NWM 200 Number of flower heads 150 100 50 0 May Jun Jul Aug
Surface matting
4 3 Surface cover (cover class) Surface cover Surface matting >25-50% >5-25% 2017 2018 >1-5% 2 >0-1% 1 0 EWM HWM NWM
4 3 Surface cover (cover class) Surface cover Surface matting >25-50% >5-25% b 2017 2018 >1-5% 2 a >0-1% 1 b 0 EWM HWM NWM
4 3 Surface cover (cover class) Surface cover Surface matting >25-50% >5-25% c 2017 2018 >1-5% 2 a >0-1% 1 b 0 EWM HWM NWM
>50-75% 2017 2018 HWM EWM >25-50% NWM >5-25% Surface cover >1-5% >0-1% 0 Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
>50-75% 2017 2018 HWM EWM >25-50% NWM >5-25% Surface cover >1-5% >0-1% 0 Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep
Results below the surface
100 2017 2018 HWM EWM 80 NWM 60 Stems / m 40 20 0 Jul Aug Sep Oct Nov Dec Jan Feb
100 2017 2018 HWM EWM 80 NWM 60 Stems / m 40 20 0 Jul Aug Sep Oct Nov Dec Jan Feb
Conclusions HWM produces more flowers and flowers earlier than EWM and NWM Varies by year HWM has greater surface matting than EWM and NWM Varies by year Consistently greater than NWM HWM produces an intermediate number of stems
Conclusions Field-based evidence of hybrid vigor HWM appears more invasive than parental EWM Earlier and increased flowering may increase HWM spread and provide a competitive advantage Increased surface matting may shade out natives more than EWM More aggressive management may be needed for HWM infested lakes Knowledge of which lakes have HWM is important Crucial to distinguish HWM from EWM and NWM
Acknowledgements UMN Carli Wagner Michael Verhoeven Rafael Contreras-Rangel Carolyn Kalinowski Noah Berg Ranjan Muthukrishnan Jasmine Eltawely Ray Newman MNDNR Keegan Lund Kylie Cattoor April Londo Mike Netherland, University of Florida Rachael Crabb, Minneapolis Parks and Recreation Board Eric MacBeth, City of Eagan Adam Robbins, City of Saint Paul