Design and testing of field application tools for a bioherbicide with a plant virus as active ingredient

SolviNix LC is a novel commercial bioherbicide containing a plant virus as the active ingredient (ai). It is registered in the USA for the control of tropical soda apple (Solanum viarum, TSA), an invasive weed of pastures and woodlands. As no prior example or experience exists for the application of a plant virus as an herbicide, we devised and tested tools and methods for field application. Our objectives were to design a practical, economical, and effective tool and method that could be easily melded into weed management practices. This should be accomplished by delivering a minimal effective amount of the ai (in dosage and rate). As TMGMV, like all plant viruses, requires physical damage to the plant by abrasion or wounds to enter the tissues, we designed, assembled, and tested four tools and a few modifications thereof that simultaneously abraded and applied the bioherbicide to the leaves. We also tested two commercially available herbicide wipers and modifications to them to treat individual plants. Of the tools tested, high-pressure sprayers, either a backpack sprayer or an all-terrain vehicle (ATV) mounted sprayer, delivering the herbicide at > 0.55 MPa (>80 psi), provided the desired level of weed kill (85% or higher). Here we describe the different application tools, the test results, and the rationale for the application tool/method presently included in the label, a backpack sprayer. Given the novelty of the application systems we tried, this report could be instructive to others facing a similar challenge.