Mulch Depth Affects Weed Germination

Abstract

With environmental concerns increasing, non-chemical weed control in container plant production is increasing in the United States. Pine bark mini-nuggets were evaluated as a non-chemical weed control technique for two weed species; Chamaesyce maculata (L.) Small (spotted spurge) and Eclipta alba (L.) Hassk.(eclipta). On June 19, 2006, seed (25 per container) were directly placed on the potting substrate surface of #3 containers before mulching with pine bark mini-nuggets to a depth of either 0, 1.27 or 2.54 cm (0, 0.5 or 1.0 in). Additional treatments consisted of applying the mini-nugget mulch at either 1.27 or 2.54 cm (0.5 or 1.0 in) on the potting substrate then overseeding with either spotted spurge or eclipta. Eclipta number per container were 87% less 60 days after seeding (DAS) with the 1.0 in mulch depth compared to non-mulched. Furthermore, spotted spurge fresh weight (FW) was reduced by 45 and 87% (0.5 and 1.0 in, respectively) compared to the non-mulched treatment. The experiment was repeated on August 30 and spurge number per container was 90% less 60 DAS in the 1.0 inch mulch treatment compared to the non-treated containers. A third and fourth experiment also demonstrated that pine bark mini-nuggets have potential to provide non-chemical weed control in nursery crops grown in #3 containers. Results, suggest that with proper application pine bark mini-nuggets can enhance weed control in container nurseries.

Emergence of garden spurge (Euphorbia hirta) and large crabgrass (Digitaria sanguinalis) in response to different physical properties and depths of common mulch materials

“…Depths of at least 2.5 cm were required for PB and PS to achieve at least 60% reduction in emergence of garden spurge and crabgrass in outdoor and greenhouse experiments. This result is similar to previous findings with flexuous bittercress, yellow woodsorrel (Oxalis stricta L.) (Richardson et al 2008), and spotted spurge (Cochran et al 2009), in which PB depths of at least 2.5 cm were needed to reduce germination of top-positioned seed. At PB depths of ≤1.3 cm, data reported by Cochran et al (2009) and Richardson et al (2008) are in agreement with data reported here, suggesting that many weed species will be able to germinate and could possibly root into soil beneath such a shallow mulch depth.…”

“…This result is similar to previous findings with flexuous bittercress, yellow woodsorrel (Oxalis stricta L.) (Richardson et al 2008), and spotted spurge (Cochran et al 2009), in which PB depths of at least 2.5 cm were needed to reduce germination of top-positioned seed. At PB depths of ≤1.3 cm, data reported by Cochran et al (2009) and Richardson et al (2008) are in agreement with data reported here, suggesting that many weed species will be able to germinate and could possibly root into soil beneath such a shallow mulch depth. Shallow mulch depths (≤1.3 cm) may also allow seeds to be washed beneath mulch layers where they may germinate and emerge from the soil beneath the mulch, as the physical barrier would be minimal.…”

“…However, regardless of depth, the physical properties of the material will undoubtedly play a critical role in weed control efficacy. For example, pine bark (PB) processed through a screen size large enough to be considered mulch (typically >2.5 cm) provides over 90% control of many common nursery weed species (Cochran et al 2009). In contrast, PB processed to be used as potting media (particle size often 1 to 1.3 cm) has no detrimental influence on weed growth, as evidenced by the challenging nature of weed control in container-grown ornamentals (Case et al 2005).…”

Fertilizer placement affects growth and reproduction of three common weed species in pine bark–based soilless nursery substrates

“…Due to the cost of hand weeding and challenges associated with PRE herbicides, growers and researchers have investigated use of various nonchemical tools for weed control, including organic mulch such as pine bark (Cochran et al 2009;Richardson et al 2008;Wilen et al 1999), rice hulls (Case et al 2005), and weed disks or similar products that are secured on the container medium surface (Amoroso et al 2009;Chong 2003;Mathers 2003). All of these methods have been found to be as or more effective than a single herbicide application, but cost and availability often prohibit widescale adoption (Stewart et al 2017).…”

Efficacy and Estimated Annual Cost of Common Weed Control Methods in Landscape Planting Beds

“…In addition to improving plant growth (Greenly and Rakow, 1995), organic mulches have been shown to reduce weed seed germination (Cochran et al, 2009;Richardson et al, 2008) through light exclusion, reduction of available water for weed seeds, allelopathy, and by acting as a barrier to emerging seedlings (Chalker-Scott, 2007). The exact method in which mulches reduce weed growth is not known for all mulch types, but light exclusion has been attributed as being the most common method (Teasdale and Mohler, 2000) as most weed seeds require light to germinate (Wesson and Wareing, 1967).…”