Spring treatments of diquat and endothall for curlyleaf pondweed control

Abstract

Spring treatments of the contact herbicides diquat and endothall were effective in reducing curlyleaf pondweed (Potamogeton crispus L.) shoot and root biomass, as well as suppressing turion production. An outdoor mesocosm study was conducted in the spring of 1999 in which plants were treated during three different periods using two rates of each product (either 1 or 2 mg ai L-1). Water temperatures ranged from 16 to 23C during applications. All diquat applications reduced shoot biomass by 60% and root biomass by 60 to 90% compared to the untreated reference. Turion numbers decreased by 85%. All endothall applications reduced shoot and root biomass; however, early and mid-spring treatments provided better control than late spring treatments. Both the earlier endothall treatments reduced shoot and root biomass by 90% versus a 60% reduction in shoot and root biomass for the late spring endothall treatment. Consequently, turion numbers decreased significantly with the early and mid-spring endothall treatments (>90%), but not with the late spring endothall treatment. This study is further evidence that both diquat and endothall could be applied early in the growing season to reduce turion formation and provide for potential long-term control of curlyleaf pondweed.