Short-term Preemergence Herbicide Adsorption by Mulch Materials and Impacts on Weed Control

Abstract

<jats:p>The objective of this research was to determine how mulch type affects adsorption and efficacy of commonly used preemergence herbicides in nurseries and landscapes. Nursery containers were filled with standard potting media and mulched with either pine bark (PB) mini-nuggets (mixed <jats:italic>Pinus</jats:italic> sp.), pine straw (PS; mixed <jats:italic>Pinus</jats:italic> sp.), or shredded eucalyptus hardwood (HW; <jats:italic>Eucalyptus</jats:italic> sp.) at a 2-inch depth. Herbicides including dimethenamid-P + pendimethalin (applied as a tank mix), prodiamine, and indaziflam were applied to mulched containers, watered in, and the mulch was subsequently removed 3 days later. Seeds of garden spurge (<jats:italic>Euphorbia hirta</jats:italic>), large crabgrass (<jats:italic>Digitaria sanguinalis</jats:italic>), and eclipta (<jats:italic>Eclipta prostrata</jats:italic>) were then seeded and used as bioassay species for dimethenamid-P + pendimethalin, prodiamine, and indaziflam, respectively. Chemical assays were also performed using a separate set of pots mulched with PB at 2 inches and treated with the same herbicides. Results from the bioassay experiment showed PS was the only mulch type that did not significantly decrease efficacy of any applied herbicide. Chemical assays showed only 34% of the applied dimethenamid-P reached the soil surface as evidenced by chemical assay, but more dimethenamid-P moved through PB than did pendimethalin (12%) or prodiamine (17%), which adsorbed more strongly. Overall results suggest preemergence herbicides will be strongly adsorbed to organic mulch. However, as mulch is typically more effective on weeds that germinate below the mulch layer, this does not automatically result in reduced efficacy from herbicide + mulch combinations, and the addition of a preemergence herbicide may be effective in reducing weed germination within or on top of the mulch layer.</jats:p>

Improving Pennsylvania Bittercress Weed Control Efficacy with Mulch and Herbicide in Containers

“…Less isoxaben may have adsorbed to the pine bark mulch due to its lower K oc , whereas prodiamine likely had a higher adsorption to the mulch and was unavailable on the soil surface to provide control of germinating seedlings. This has been reported previously, where prodiamine applied on top of a pine bark mulch provided only 60% control of large crabgrass compared with 100% control when applied to the soil surface (Saha et al, 2019b). This same effect was not observed with rice hulls, which tended to provide close to 100% Pennsylvania bittercress control regardless of herbicide application.…”

“…Rice hulls provided better control of Pennsylvania bittercress compared with both pine bark and the use of either herbicide alone on almost all evaluation dates for all parameters collected. Mulch provides weed control through several mechanisms, including light exclusion, providing a physical barrier, and reducing available moisture, which all depend on mulch type, weight to area ratio, application depth, seed placement, and particle size (Chalker-Scott, 2007;Ngouajio and Ernest, 2004;Saha et al, 2019b;Teasdale and Mohler, 2000). As rice hulls are hydrophobic, the primary mechanism of control they provide is reducing available moisture for weed seed germination, explaining why emergence is typically lower when seeds are placed on top of rice hulls compared with when seeds are placed below the rice hulls layer (Altland and Krause, 2014; Altland et al, 2016).…”

“…As rice hulls are hydrophobic, the primary mechanism of control they provide is reducing available moisture for weed seed germination, explaining why emergence is typically lower when seeds are placed on top of rice hulls compared with when seeds are placed below the rice hulls layer (Altland and Krause, 2014; Altland et al, 2016). In contrast, pine bark has been shown to provide better weed control when seeds are placed beneath the mulch as it serves as a strong physical barrier to emergence (Saha et al, 2019a(Saha et al, , 2019b. While in a landscape it would be more important for a mulch to suppress emergence of weed seeds below the mulch as there would likely be a seed bank in a field soil, in a nursery environment the potting soil would ideally be weed free, at least at potting; thus, it would be more important to have a mulch that is more efficacious on seeds introduced on top of the mulch layer over time, such as rice hulls.…”

“…with the addition of pine bark mini-nuggets at 3 inches led to 100% bittercress control, a higher control level compared with applying herbicide alone, which resulted in 92% control (Richardson et al, 2008). However, many of these studies have focused on mulch materials more suitable for a landscape planting bed as opposed to materials suited for container nurseries (Saha et al, 2019a(Saha et al, , 2019b.…”

Annual bluegrass control in bermudagrass using dimethenamid and pendimethalin

“…], large crabgrass [ Digitaria sanguinalis (L.) Scop. ], garden spurge ( Euphorbia hirta L.), and eclipta ( Eclipta prostrata L.) (Saha, Marble, Stewart, & Chandler, 2017; Saha et al., 2019). In turfgrass, FreeHand effectively controlled simazine (6‐chloro‐2‐ N ,4‐ N ‐diethyl‐1,3,5‐triazine‐2,4‐diamine)‐resistant ABG when applied preemergence in a zoysiagrass ( Zoysia spp.)…”