Can herbicide usage be reduced by practicing IPM for waterhyacinth (Eichhornia crassipes) control?

Lyn A. Gettys, Phillip W. Tipping, Carl J. Della Torre III, Samantha N. Sardes, Kyle M. Thayer


Waterhyacinth is the most intensively managed floating aquatic weed in Florida, with around $3.45 million spent in Florida during FY 2011–2012 for maintenance control of floating aquatic weeds – primarily waterhyacinth and waterlettuce (Pistia stratiotes)—in public waters. Thus, even a small reduction in herbicides used for control of waterhyacinth could represent significant savings. Biological control of waterhyacinth using insects has been used in many countries and feeding damage associated with insects often renders affected plants more susceptible to stressors, including herbicides. Although herbicides and biological control have been evaluated separately on waterhyacinth, there is little information regarding the combined effects of these control methods in an integrated pest management program. Therefore, the objective of these experiments was to evaluate the impact of combining biological control agents with different rates of 2,4-D on waterhyacinth growth and development. We evaluated two levels of biocontrol [control (no biocontrol agents) versus biocontrol (unrestricted attack by Neochetina sp. weevils and Megamelus scutellaris)] and three 2,4-D rates [control (no herbicide); low rate [2 quarts per acre (qpa)] and operational rate (4 qpa)] in these experiments. Five replicates were prepared for each combination of treatments and were arranged in a completely randomized design in concrete mesocosms. Plant dry biomass three months after 2,4-D applications revealed that plants treated with either rate of 2,4-D only (no insects) recovered from the herbicide treatments and had about 50% as much biomass as untreated plants, but there was little or no regrowth in plants treated with insects plus either rate of 2,4-D. These results suggest that operational rates of 2,4-D could be reduced from 4qpa to 2qpa with little potential for waterhyacinth regrowth, provided biocontrol insects are present on the populations targeted for treatment.


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Proc. Fla. State Hort. Soc.     ISSN 0886-7283