Mulch provides many benefits to landscape ornamentals, including soil temperature regulation (Fraedrich and Ham, 1982; Montague and Kjelgren, 2004), increased soil moisture (Fraedrich and Ham, 1982; Iles and Dosmann, 1999; Kraus, 1998; Litzow and Pellett, 1993; Watson, 1988; Watson and Kupkowski, 1991), and improved overall plant growth and survival (Green and Watson, 1989; Greenly and Rakow, 1995; Litzow and Pellett, 1993). Similarly, mulch increases the growth of container-grown ornamentals by providing the same benefits in a production (i.e., nursery) environment (Amoroso et al., 2010; Lohr, 2001).
Mulch is most often applied in landscape planting beds for aesthetic purposes and for weed management (Chalker-Scott, 2007). Mulch is less commonly used in container nursery production but may be used as a nonchemical weed management option for sensitive plant species (Case et al., 2005). Many different mulch materials have been evaluated for weed control in container plants. Richardson et al. (2008) reported up to 150 d of yellow woodsorrel (Oxalis stricta) and hairy bittercress (Cardamine hirsuta) control in large (3–7 gal) container-grown ornamentals with 3 inches of PB mini-nuggets. Similarly, Cochran et al. (2009) showed that 1 inch of PB mulch reduced garden spurge and eclipta fresh weights (FWs) and weed counts by more than 80% compared with a nonmulched control. Reviews of different mulch materials as a sole means for weed control have been summarized for landscape (Chalker-Scott, 2007) and nursery production (Case et al., 2005).
A review of earlier research focusing on the use of mulch in combination with, or in comparison with, PRE herbicides was recently published by Marble (2015). In many cases, research focused on evaluating different mulch or herbicide + mulch combinations to determine the most effective on target weed species, or evaluated the use of herbicide-treated mulches (Case and Mathers, 2006a, 2006b). For example, Bartley et al. (2017) evaluated three different mulch types applied at three depths (1, 2, and 4 inches) with and without addition of dimethenamid-P. The authors reported that 168 d after treatment (DAT), herbicide was no longer a significant factor as dimethenamid-P had lost all efficacy, and mulch depth was the only significant factor, with depths of 1–4 inches providing 90% to 100% spotted spurge (Euphorbia maculata) control for up to 90 d after seeding. All of these previous reports establish that different herbicide + mulch combinations can potentially provide a high level of control of many different weed species.
Previous studies have shown that mulch can provide substantial weed control when applied alone at adequate depths (Cochran et al., 2009; Richardson et al., 2008; Wilen et al., 1999); however, it is unclear whether it is mulch or herbicide that contributed most to the observed weed control. Furthermore, a decrease in herbicide efficacy with certain herbicides such as dinitroanilines, which bind tightly to mulch, can occur with increased levels of organic matter on the soil surface. Consequently, the herbicide becomes unavailable for weed control (Buhler, 1992). Mulch depth is an important factor to consider as research conducted by Banks and Robinson (1986) and Chauhan and Abugho (2012) showed that application of thin mulch layers reduces PRE efficacy in several agronomic studies because of rapid degradation caused by increased microbial activity (Locke and Bryson, 1997). Alternatively, herbicide placement (i.e., application of herbicides under mulch) or making the application before mulch addition improves weed control compared with PRE application on top of mulch (Chen et al., 2013). However, in most landscape situations, this application could only be made initially, and subsequent applications would have to be applied on top of existing mulch layers.
Increasing posttreatment irrigation levels to mulched areas could be a means of increasing herbicide concentrations in the soil as PRE herbicides must be incorporated into the soil by irrigation following application. In most cases, PRE herbicide labels recommend irrigation volumes of 0.2–0.5 inches soon after application. Banks and Robinson (1986) reported that reduced amounts of acetochlor, alachlor, or metolachlor were received on the soil surface as wheat (Triticum aestivum) straw mulch depth increased, resulting in the need for higher irrigation volumes for thicker mulch layers. However, wheat straw has very different physical properties compared with common landscape mulch materials, and the herbicides that were evaluated are not commonly applied in landscape situations. Additional research is required to determine the extent to which activation irrigation can improve the efficacy of different herbicide + mulch combinations commonly used in landscapes and container nurseries. This experiment was designed to accomplish three primary objectives. First, we wanted to determine the efficacy of multiple herbicide + mulch combinations and determine which factors significantly affected the control, specifically focusing on herbicide formulation and posttreatment irrigation volumes. Second, we wanted to determine the efficacy derived from mulch or herbicides used alone under the same conditions as the herbicide + mulch combinations. Third, our goal was to identify differences in the additive effects of the herbicide + mulch combinations compared with the use of only herbicides or only mulch.
Amoroso, G., Frangi, P., Piatti, R., Fini, A. & Ferrini, F. 2010 Effect of mulching on plant and weed growth, substrate water content, and temperature in container-grown giant arborvitae HortTechnology 20 957 962
Banks, P.A. & Robinson, E.L. 1986 Soil reception and activity of acetochlor, alachlor, and metolachlor as affected by wheat (Triticum aestivum) straw and irrigation Weed Sci. 34 607 611
Bartley, III P.C., Wehtje, G.R., Murphy, A.M., Foshee, W.G. III & Gilliam, C.H. 2017 Mulch type and depth influences control of three major weed species in nursery container production HortTechnology 27 465 471
Black, J.N. 1956 The influence of seed size and depth of sowing on pre-emergence and early vegetative growth of subterranean clover (Trifolium subterraneum L.) Austral. J. Agr. Res. 7 98 109
Buhler, D.D. 1992 Population dynamics and control of annual weeds in corn (Zea mays) as influenced by tillage systems Weed Sci. 40 241 248
Burrows, M. 2017 Evaluation of pine bark mulch-herbicide combinations for weed control in nursery containers. Auburn Univ., Auburn, AL, Master’s Thesis
Case, L.T. & Mathers, H.M. 2006a Field evaluation of herbicide treated mulches. Proc. Southern Nursery Assn. Res. Conf. 51:402–405
Chauhan, B.S. & Abugho, S.B. 2012 Interaction of rice residue and pre herbicides on emergence and biomass of four weed species Weed Technol. 26 627 632
Chauhan, B.S. & Johnson, D.E. 2008 Germination ecology of southern crabgrass (Digitaria ciliaris) and Indian crabgrass (Digitaria longiflora): Two important weeds of rice in the tropics Weed Sci. 56 722 728
Chen, Y., Strahan, R.E. & Bracy, R.P. 2013 Effects of mulching and preemergence herbicide placement on yellow nutsedge control and ornamental plant quality in landscape beds HortTechnology 23 651 658
Cochran, D.R., Gilliam, C.H., Eakes, D.J., Wehtje, G.R., Knight, P.R. & Olive, J. 2009 Mulch depth affects weed seed germination J. Environ. Hort. 2 85 90
Ferguson, J., Rathinasabapathi, B. & Warren, C. 2008 Southern redcedar and southern magnolia wood chip mulches for weed suppression in containerized woody ornamentals HortTechnology 18 266 270
Green, T.L. & Watson, G.W. 1989 Effects of turfgrass and mulch on establishment and growth of bare root sugar maples J. Arboric. 15 268 272
Holm, L.G., Plucknett, D.L., Pancho, J.V. & Herberger, J.P. 1977 The world’s worst weeds. Distribution and biology. Univ. Press Hawaii, Honolulu, HI
Iles, J.K. & Dosmann, M.S. 1999 Effect of organic and mineral mulches on soil properties and growth of ‘Fairview Flame R’ red maple trees J. Arboric. 25 163 167
Marble, S.C. 2015 Herbicide and mulch interactions: A review of the literature and implications for the landscape maintenance industry Weed Technol. 29 341 349
Marble, S.C., Koeser, A.K. & Hasing, G. 2015 A review of weed control practices in landscape planting beds: Part I – Non-chemical weed control methods HortScience 50 851 856
Marble, S.C., Koeser, A.K., Hasing, G., McClean, D. & Chandler, A. 2017 Efficacy and estimated annual cost of common weed control methods in landscape planting beds HortTechnology 27 199 211
Montague, T. & Kjelgren, R. 2004 Energy balance of six common landscape surfaces and the influence of surface properties on gas exchange of four containerized tree species Scientia Hort. 100 229 249
Neal, J., Chong, J.C. & Williams-Woodward, J. 2017 2017 Southeastern U.S. pest control guide for nursery crops and landscape plantings. 19 Dec. 2018. <https://content.ces.ncsu.edu/southeastern-us-pest-control-guide-for-nursery-crops-and-landscape-plantings/complete-southeastern-us-pest-control-guide>
Richardson, B., Gilliam, C.H., Fain, G.B. & Wehtje, G.R. 2008 Container nursery weed control with pinebark mini-nuggets J. Environ. Hort. 26 144 148
Saha, D., Marble, C., Boyd, N.S. & Steed, S. 2016 Impacts of preemergence herbicide formulation on cost and weed control efficacy for container nursery crop producers Proc. Intl. Plant Prop. Soc. 66 319 324
Smith, D.R., Gilliam, C.H., Edwards, J.H., Olive, J.W., Eakes, D.J. & Williams, J.D. 1998 Recycled waste paper as a non-chemical alternative for weed control in container production J. Environ. Hort. 16 69 75
Somireddy, U. 2012 Effect of herbicide-organic mulch combinations on weed control and herbicide persistence. Ohio State Univ., Columbus, OH, PhD Diss
Wehtje, G.R., Gilliam, C.H., Murphy, A.M. & Fausey, J. 2015 Preemergence control of spotted spurge (Chamaesyce maculata) with flumioxazin as influenced by formulation and activation moisture Weed Technol. 29 108 114
Yang, Q., Gilliam, C.H., Wehtje, G.R., McElroy, J.S., Sibley, J.L. & Chamberlin, J. 2013 Effect of pre and post moisture level on preemergence control of hairy bittercress (Cardamine hirsuta L.) with flumioxazin J. Environ. Hort. 31 49 53