Preemergence Control of Spotted Spurge (Chamaesyce maculata) with Flumioxazin as Influenced by Formulation and Activation Moisture

Abstract

Flumioxazin is commonly used in nursery production for PRE weed control. Container nursery producers are of the opinion that the granular formulation is less effective than the sprayable formulation. Under the hypothesis that the granular formulation may require more water for activation, an experiment was conducted to evaluate the interaction of flumioxazin formulation, rate, and activation moisture for PRE control of spotted spurge in a pine-bark substrate. Experiment consisted of a factorial arrangement of four experimental variables; flumioxazin formulation (granular and spray), and flumioxazin rate (0.28 and 0.42 kg ai ha−1), substrate moisture level at the time of application (dry, medium, and wet), and after-application irrigation level (a single irrigation at 0.6, 1.3, 2.5, and 5.1 cm). Treated pots were seeded with spotted spurge 2 d after the herbicide application, which was 1 d after the first irrigation. Control as indicated by spotted spurge counts and fresh weight was influenced only by flumioxazin rate and formulation. The sprayable formulation provided excellent control regardless of rate. Granular formulation was generally less effective, and additional activation moisture did not improve efficacy. Further studies were conducted with the granular formulation to determine the maximum separation distance between the spotted spurge seed and herbicide prills at which control is possible. Individual prills and spotted spurge seeds were placed on media surface at progressively increasing separation distances. Nonlinear regression of seedling survival data revealed that ≥99% control required a prill–seed separation of ≤5.2 mm. This prill–seed separation requirement is only marginally obtained with the current registered rate, i.e., 0.42 kg ai ha−1 or 168 kg product ha−1. The relationship between control and prill–seed separation distance cannot be manipulated by additional activation moisture. Inadequate contact between the spotted spurge seeds and the flumoioxazin-containing prills is likely the sole cause of inadequate control.

Mulch Type and Depth, Herbicide Formulation, and Postapplication Irrigation Volume Influence on Control of Common Landscape Weed Species

“…The use of spray-applied formulations of indaziflam, prodiamine, or dimethenamid-P + pendimethalin resulted in an increase in control of 42%, 17%, and 13% for eclipta, large crabgrass, and garden spurge, respectively, in comparison with the granular formulation. These findings are consistent with earlier reports evaluating flumioxazin in which greater control was consistently achieved with spray-applied formulations compared with a granular formulation (Wehtje et al, 2015).…”

“…Based on these results across all three species, herbicide formulation will have a greater influence on weed control than irrigation, similar to previous reports (Saha et al, 2016;Wehtje et al, 2015;Yang et al, 2013). Although some irrigation effects were noted in garden spurge treated with dimethenamid-P + pendimethalin, all irrigation levels resulted in commercially acceptable weed control and would have little practical importance.…”

“…However, higher variability in eclipta control could be because while indaziflam is effective for eclipta control, it is typically slightly less efficacious on eclipta than prodiamine is on large crabgrass or dimethenamid-P + pendimethalin is on garden spurge (Neal et al, 2017), and this variability may have led to greater variability in results. Granular herbicides are often less effective than spray-applied herbicides because granules need to be uniformly dispersed on the soil surface and in adequate quantities so that the herbicidal active ingredient is in close proximity to germinating seedlings (Wehtje et al, 2015). Although it was not recorded, it is possible that the higher irrigation volume of 2 inches may have slightly dispersed granules inside the pots, resulting in less weed control.…”

“…The influence of posttreatment irrigation on granular herbicide formulations likely depends on the weed species and herbicide. Wehtje et al (2015) reported that higher posttreatment irrigation levels had no influence on the efficacy of a granular flumioxazin application for spotted spurge (Euphorbia maculata) but did for bittercress (C. hirsuta) (Yang et al, 2013). Although posttreatment irrigation may play a role in granular efficacy, it appears that any effects would be minimal if the required amount of irrigation that is needed to activate the herbicide were applied.…”

Mulch Type and Depth Influences Control of Three Major Weed Species in Nursery Container Production

“…To reduce the need for hand weeding, nursery growers typically rely on multiple applications of preemergence herbicides to reduce weed pressure. Preemergence herbicides are commonly broadcast in a granular form using a cyclone or ''bellygrinder''-type rotary spreader despite more recent research revealing the ineffectiveness of some granular applications when compared with liquid formulations and applications (Wehtje et al, 2015). There are numerous problems associated with current application methods of preemergence herbicides including improper handling of materials and application procedures, injury to nontarget plants, and nontarget loss (Wooten et al, 1999).…”