Spray Retention and its Potential Impact on Bioherbicide Efficacy

Hydraulic spray systems are widely used for application of agrochemicals due to ease of operation and consistent performance, despite relative inefficiency in delivering pest-control products to intended targets. Frequently, spray parameters are optimized for maximum product deposition and retention, although success of this strategy is case dependant. There is limited information on application improvements for microbial pesticides (biopesticides). Biopesticides, especially those that employ a fungus as the active ingredient, are generally applied with a liquid carrier but their deposition or retention has rarely been characterized. Depending on the size of microbe and plant morphology or architecture, interactions among spray parameters can be complex in terms of the impact on retention, distribution and performance of the biopesticide agent. Extrapolation of information from chemical pesticide applications may not always be appropriate. This review, based primarily on authors’ experience in spray retention involving three bioherbicide-weed systems, is aimed to highlight the impact of spray parameters and additives (adjuvants) on deposition, retention, and efficacy of bioherbicide agents. Information from additional bioherbicide agents is also considered for different sizes of fungal inoculum or characteristics of target plants. Although the focus is on potential bioherbicides, the information may also be useful to application of other microbe-based biopesticide agents. Strategies for maximizing biocontrol efficacy through optimization of spray parameters as well as other application technologies are discussed. _____________________________________________________________________________________________________________