Brazilian egeria herbicide mesocosm and field trials for managing the Sacramento-San Joaquin River Delta

Authors: Madsen, John; MORGAN, CHRISTY - University Of California, Davis; MISKELLA, JOHN - University Of California, Davis; KYSER, GUY - University Of California, Davis; GILBERT, PATRICIA - California Department Of Boating And Waterways; O BRIEN, JON - California Department Of Boating And Waterways; GETSINGER, KURT - Us Army Engineer Research And Dvelopment Center

Submitted to: Journal of Aquatic Plant Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2020
Publication Date: 8/31/2021
Citation: Madsen, J.D., Morgan, C., Miskella, J., Kyser, G., Gilbert, P., O'Brien, J., Getsinger, K.D. 2021. Brazilian egeria herbicide mesocosm and field trials for managing the Sacramento-San Joaquin River Delta. Journal of Aquatic Plant Management. 59s:90–97.

Interpretive Summary: We tested eleven different aquatic herbicides in an outdoor tank experiment to control Brazilian egeria over a ten week period. The six best herbicides (in ranked order) for control were fluridone, diquat, dimethylalkylamine salt of endothall, complexed copper, carfentrazone-ethyl, and the dipotassium salt of endothall. Selecting three herbicides that meet the environmental constraints of the Sacramento-San Joaquin River Delta, we tested three herbicides in plots around the Delta. A study of three treatment plots in 2016 found an 85% reduction in biomass in fluridone-treated plots, compared to a 26% increase in biomass in untreated plots. A field trial on two plots treated with diquat found 98% and 80% control, respectively. A field trial with the dipotassium salt of endothall resulted in 43% control after one treatment.

Technical Abstract: The nonnative Brazilian egeria (Egeria densa Planch.) is the dominant submersed plant in the Sacramento - San Joaquin River Delta, displacing native plant species and degrading habitat for endangered fish species. A mesocosm study was conducted at the USDA facility in Davis, CA to determine efficacy of aquatic herbicides on egeria. Fifty mesocosm tanks of 167 L capacity were planted with four 4.2 L pots of . Four tanks each were treated with bispyribac sodium (45 µg L-1), carfentrazone-ethyl (200 µg L-1), ethylenediamine complex of copper (1000 µg L-1), diquat (390 µg L-1), dipotassium salt of endothall (5000 µg L-1), dimethylalkylamine salt of endothall (5000 µg L-1), florpyrauxifen-benzyl (50 µg L-1), flumioxazin (400 µg L-1), fluridone (60 µg L-1), imazamox (500 µg L-1), penoxsulam (60 µg L-1), and four tanks were an untreated reference. All were single treatments, static exposures for ten weeks. At the end of ten weeks, all pots were harvested, and the shoots were dried at 70C for 48 hours. All herbicides produced some statistically significant reduction in biomass. Copper, diquat, endothall dimethylalkylamine, and fluridone produced >90% control. Carfentrazone (69%) and the potassium salt of endothall (62%) provided better than 50% control, with other herbicides producing somewhat less than 50% control. Field demonstration has substantiated some of these findings. A study of three treatment plots in 2016 found an 85% reduction in biomass in fluridone-treated plots, compared to a 26% increase in biomass in untreated plots. A field trial on two plots treated with diquat found 98% and 80% control, respectively. A field trial with the dipotassium salt of endothall resulted in 43% control after one treatment.