Evaluation of Pine Bark Mulch-Herbicide Combinations for Weed Control in Nursery Containers
Type of DegreeMaster's Thesis
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Weed control is a continuing challenge for greenhouse, field, and container nursery growers across the United States. Weed control techniques in container grown ornamentals include hand pulling, herbicide applications, and utilizing mulches. The practices each bring a unique challenge including labor costs associated with hand pulling, herbicide non-target loss, herbicide resistant weeds, and improper calibration of sprayers and spreaders. Research has shown that wood-based mulches can successfully control weeds both with and without addition of preemergence herbicides (Bartley et al., 2014). The research presented addresses the effects of utilizing mulches in combination with preemergence herbicides. By identifying preemergence herbicides that work effectively with pine bark mini-nugget mulch, growers may be able to increase weed control effectiveness and longevity in container grown nursery stock. The research presented also addresses the effect of preemergence herbicide application timing to pine bark-based mulches on weed control. The objective of this research is to evaluate the weed control efficacy of three preemergence herbicides, formulations of those herbicides, and herbicide application timing in conjunction with 5 cm (2 in.) of a commercially available pine bark mini-nugget mulch for control on long stalk phyllanthus (Phyllanthus tenellus), spotted spurge (Chamaesyce maculata), or eclipta (Eclipta prostrata). On 14 May, all containers were treated with the appropriate herbicide recommended label rate either below or above 5 cm (2 in.) of a pine bark mininugget mulch (Hood Landscaping Products, Adel, GA). Liquid herbicide treatments included dimethenamid-P (Tower®; BASF Corp., Research Triangle Park, NC) + pendimethalin (Pendulum® Aquacap™; BASF, Corp.) (1.7 kg/ha, 12.2 kg/ha) (1.5 lbs ai/A, 3.3 lbs ai/A), indaziflam (Marengo® SC, Bayer Crop Science, Research Triangle Park, NC) (0.08 kg/ha) (0.07 lbs ai/A), and flumioxazin (SureGuard®; Valent Corp., Walnut Creek, CA) (0.43 kg/ha) (0.38 lbs ai/A) and were applied using a CO2 pressure backpack sprayer at 30 gallons per acre. Granular herbicide treatments also included dimethenamid-P + pendimethalin (Freehand®; BASF, Corp.) (1.7 kg/ha, 2.2 kg/ha) (1.5 lbs ai/A, 2lbs ai/A), indaziflam (Marengo® G, Bayer Crop Science) (0.08 kg/ha) (0.07 lbs ai/A), and flumioxazin (Broadstar™; Valent, Corp.) (0.42 kg/ha) (0.38 lbs ai/A) and were applied using a handheld shaker. For all three weed species, weed count and fresh weight means were not different when any herbicide was treated below or above an application of mulch. Generally, shoot fresh weight and weed count were similar between all herbicidemulch combinations and mulch alone containers. For most fresh weights and weed counts of different placements or herbicides linear or quadratic trends increase up to 30-60 DAT then steadily declined at 90, 120, and 150 DAT. This is thought to be caused by shortened day length and the continuing depletion of available controlled released fertilizer throughout the year. Indaziflam, liquid or granular, and liquid flumioxazin consistently provided smaller shoot fresh weight and weed count that either formulation of flumioxazin.