Alternative Mulch Species, With and Without Dimethenamid-p, for Weed Control in Nursery Container Production

Abstract

Weed control has been a persistent problem in the nursery industry. These antagonistic weeds incur many challenges and cost to control them as well as reducing the container plants marketability (Neal, 1999; Simpson et al, 2002). The necessity to control weeds in container plant production has propelled two nursery management practices, hand pulling and herbicide applications. There are numerous problems associated with current weed control practices including increasing labor cost, herbicide resistant weeds, misapplications, injury to non-target plants, and environmental concerns. Mulches may have potential to be valuable assets in the struggle to reduce labor costs, effectively control weeds, and reduce the negative environmental impacts of current practices. Pine bark mini-nuggets, as with other tree-derived mulches, create an environment that is not conducive to weed seed germination due to low fertility, large particle size, and hydrophobic properties (Richardson et al., 2008). In other studies, combinations of herbicides and mulches were deemed most effective. In addition to tree-derived mulch materials such as pine bark, pine straw and hardwood chips, other readily available tree-derived mulch species such as Chinese privet (Ligustrum sinense), sweetgum (Liquidambar styraciflua), and eastern red cedar (Juniperus virginiana) could be used as mulch in container production in lieu of commercialized pine bark mini-nuggets. The objective of this study was to evaluate four readily available mulch species at multiple depths for long term weed control and phytotoxicity in container grown nursery plants. Mulch treatments were evaluated with and without dimethenamid-p herbicide (Tower®). All aforementioned mulches were tested at depths of 2.5, 5.1, or 10.2 cm (0, 1, 2, and 4 in), with and without dimethenamid-p herbicide, to determine if there were any differences among treatments through the duration of a growing season on weed counts and fresh weight of long-stalked phyllanthus (Phyllanthus tenellus), eclipta (Eclipta prostrata), and spotted spurge (Euphorbia maculata). At the first 30 day evaluation, there were no differences in treatments other than containers without mulch. Dimethenamid-p was shown to have better weed control without the addition of mulch than containers not treated with herbicide but did not increase efficacy when compared at 2.5, 5.1, or 10.2 cm (1, 2, or 4 in) of mulch. By the initiation of the second evaluation period (~45 days after treatment), dimethenamid-p had lost considerable weed control efficacy and mulch depth main effect remained significant through the third evaluation period (~160 days after treatment). Quadratic or linear trends over mulch depth indicated that weed control increased with mulch depth on all weed species across all evaluations. There were no consistent differences observed between mulch species. Mulch and herbicide effects on the growth of wax-leaf ligustrum (Ligustrum japonicum) and snowball viburnum (Viburnum macrocephalum) were evaluated separately. No phytotoxicity injury was observed at any date in the study. Plant size index indicated that dimethenamid-p treatments reduced the growth of both species by an average of 5 cm (1 in); mulch species or depth did not. Data showed that mulches prepared from any of these readily available tree species could be viable weed control options.