Smutgrass Control in Bahiagrass is Improved with Applications of Herbicide and Fertilizer

Abstract Smutgrass is an invasive weed species that can quickly outcompete bahiagrass because of its aggressive growth, prolific seed production, and rhizomatous growth. Total renovation of bahiagrass pastures or hayfields is generally not a feasible or economically viable option for most producers. Therefore, controlling the continual spread of smutgrass will require an integrated weed management plan (IWPM) that incorporates multiple strategies. The objective of this study was to test the interactions of herbicides and fertilizers on smutgrass control in bahiagrass and determine the most efficacious and economical IWPM plan for low-input bahiagrass systems. This research was conducted on a mixture of ‘Tifton 9’ and ‘Pensacola’ bahiagrass at the Alapaha Beef Station in Alapaha, GA. The study design was randomized complete block with a three by four factorial treatment arrangement with six replications. Fertility treatments included 56 kg N ha-1 (ammonium nitrate, 34% N) + 56 kg K2O ha-1, 56 kg N ha-1, and an unfertilized control. Smutgrass was reduced to <15% ground coverage when a post-emergent herbicide was applied. The addition of a pre-emergent herbicide and/or fertilizer further reduced the coverage of smutgrass (P < 0.01). As smutgrass declined, the bahiagrass ground coverage increased while other and dead material did not differ by treatment. Generally, forage accumulation and crude protein were only affected following the second N application (P < 0.01). Treatments that included pre-emergent (indaziflam) and post-emergent (hexazinone) herbicides in addition to N and K2O resulted in an improved bahiagrass stand as timely weed suppression removed competition, while fertilizer provided essential nutrients for optimum growth to fill in the gaps. Combining herbicide and fertilizer is a more economical option for producers when compared to a complete bahiagrass renovation.