This study evaluated the effects of nine alternative substrates on herbicide efficacy in container-grown nursery crops: 1) VT (pine wood chips hammer-milled to pass a 0.4-cm screen); 2) USDA (pine wood chips hammer-milled to pass a 0.64-cm screen; 3) AUC (Pinus taeda chipped including needles); 4) AUHM (AUC hammer-milled to pass a 0.48-cm screen; 5) 1 VT: 1 commercial grade pinebark (v/v); 6) 1 USDA: 1 pinebark (v/v); 7) 1 AUC: 1 pinebark (v/v); 8) 1 AUHM: 1 pinebark (v/v); and 9) 6 pinebark: 1 sand (v/v). Each substrate was amended with 6.35 kg of 17–6–12 (17N–2.6P–10K) control-release fertilizer, 2.27 kg of lime, and 0.89 kg micromax per cubic meter. Containers (8.3 cm) were filled on 15 June and three herbicides applied the next day: Rout (oxyfluorfen + oryzalin at 2.24 + 1.12 kg·ha-1), Ronstar (oxadiazon at 4.48 kg·ha-1) and a nontreated control. The next day, containers were overseeded with 25 prostrate spurge seed. Data collected included weed counts 30 and 60 days after treatment (DAT) and weed fresh weights at 60 DAT. Spurge occurred less in the two treatments of 100% pine wood chips followed by the AUC treatment. With spurge, the least weed fresh weight occurred with the USDA and AUC treatments. For example, at 30 DAT, spurge count was reduced by 33%, 40%, and 70%, respectively, when comparing VT, USDA, and AUC to pinebark: sand. Spurge fresh weight at 60 DAT followed a similar trend. With all of the substrates except AUHM, the addition of commercially used pine bark resulted in less weed control. Rout provided superior control followed by Ronstar and the nontreated control. These data show that control of prostrate spurge with commonly used preemergent applied herbicides may actually be improved with some of the alternative substrates currently being tested.
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