Herbicide Application Timings on Weed Control and Jack-O-Lantern Pumpkin Yield

Abstract

A study was conducted in a no-tillage (NT) jack-o-lantern pumpkin (Cucurbita pepo) field following winter wheat (Triticum aestivum) harvest to determine the effects of using registered herbicides at various timings on weed control and pumpkin yield. All application timings used in this study were important to maximize weed control over the pumpkin growing season. For an initial stale seedbed burndown treatment, paraquat provided better broadleaf weed control than glyphosate, which lead to greater pumpkin yields. The use of s-metolachlor + halosulfuron-methyl preemergence (PRE) and clethodim postemergence (POST) gave the best results for the second series of herbicide applications which related to higher pumpkin yields compared with none or only a PRE application. The last application timing (midseason POST-directed paraquat application between rows) also improved weed control and provided higher pumpkin yields compared with no treatment. Growers who use a stale seedbed burndown treatment in NT pumpkin production, before seedling emergence or transplanting, will generally use glyphosate although this study indicated that paraquat may prove to be a better choice depending on the weed species that are present at this application timing. Most weed control in NT pumpkin production is achieved by a PRE application of various tank-mixed herbicides for both grass and broadleaf weed control, with a POST grass herbicide, a POST application of halosulfuron-methyl, or both [for control of nutsedge (Cyperus sp.), specific broadleaf weed species, or both] applied 3 to 4 weeks later, and this study indicated that the use of labeled PRE and POST herbicides are essential to optimize weed control and pumpkin yields in NT. Most pumpkin growers do not use a POST-directed application of a nonselective herbicide (such as paraquat) before vines cover the soil surface although it appears that this application may be warranted to control weeds that have emerged later in the growing season to maximize pumpkin yield, especially if POST midseason over-the-top herbicide applications are not used. This study indicated that in addition to applying the limited PRE and POST herbicides available for weed control in pumpkin, the use of other chemical weed management practices (e.g., stale seedbed herbicide treatments or POST-directed nonselective herbicide applications) can provide valuable weed control in NT production systems and should be considered by growers to maximize pumpkin yield.