Evaluation of preemergence herbicides applied pre- and post-crimp in a rye (Secale cereale L.) cover crop system for control of broadleaf weeds in watermelons (Citrullus lanatus (Thunb.) Matsum. and Nakai)

Abstract

Field studies were conducted the spring of 2016 and 2017 at the Old Agronomy Farm (OAF) in Auburn, Alabama, and the Plant Breeding Unit (PBU) in Tallassee, Alabama to evaluate the effect of preemergence herbicide applications pre- and post-crimp in a cereal rye cover crop for control of escape weeds in watermelons. The trial consisted of an augmented factorial treatment arrangement of 3 levels of preemergence herbicides, two levels of application timing, and a nontreated control. Application timings were pre-crimp (herbicide applied prior to crimping and rolling of the cover crop) and post-crimp (herbicide applied after crimping and rolling of the cover crop). Preemergence herbicide options were ethalfluralin (1,470 g ai∙ha-1), fomesafen (180 g ai∙ha-1), and halosulfuron (39 g ai∙ha-1). A nontreated cover crop only treatment was also included yielding a total of seven treatments. Treatments were arranged in a randomized complete block design with four replications. There were no interactions among application timing and herbicide, therefore data was pooled by location. Results at the OAF location indicate application timing did not influence total weed coverage, nutsedge density, or watermelon yield. Broadleaf weed density was lower in post-crimp applied treatments 6 weeks after treatment (WAT) while grass density was lower in pre-crimp applied treatments 4 WAT. Differences were not observed at any other rating dates. Comparing individual treatments at OAF revealed yield was greatest in treatments containing fomesafen. Results at the PBU location indicated application timing did not influence nutsedge density or watermelon yield. Total weed coverage was lowest in pre-crimp applied treatments at 2, 4 and 6 WAT. Broadleaf weed density and grass density was lowest in post-crimp applied treatments 8 WAT. Comparing individual treatments revealed no significant differences among herbicides at PBU; however, all herbicides increased yield compared to the nontreated plots.