This Is AuburnElectronic Theses and Dissertations

Crop Efficacy and Weed Control Evaluation of a New Herbicide for Sensitive Herbaceous Ornamental Crops

Date

2018-11-16

Author

Penney, John R. III

Type of Degree

Master's Thesis

Department

Horticulture

Abstract

Preemergence herbicides are needed in the container nursery industry due to the high cost of hand weeding, but few preemergence herbicides are labeled for use on sensitive herbaceous ornamental crops. Currently, Snapshot® (isoxaben + trifluralin) is the only granular formulated preemergence herbicide labeled for many sensitive herbaceous ornamental crops. Fortress® (isoxaben + dithiopyr) is a new granular preemergence herbicide made by OHP, Inc. for use on sensitive herbaceous ornamental plants. In one experiment, four species of ornamental herbaceous crops in #1 containers were treated with Fortress at 150, 300, and 600 lbs/A, a spray combination of Gallery® (isoxaben) plus Dimension® (dithiopyr) at 0.75+0.38 lbs ai/A, and Snapshot (isoxaben + trifluralin) at 150 lbs/A. Also, #1 containers filled with amended 6 pine bark : 1 sand substrate were treated with Fortress at 100, 150, and 200 lbs/A, Gallery (isoxaben) plus Dimension (dithiopyr) at 0.75+0.38 lbs ai/A, and Snapshot (isoxaben + trifluralin) at 150 lbs/A and then overseeded with 25 seeds of either oxalis, bittercress, eclipta, phyllanthus, spurge, or crabgrass. Fortress had no effect on size index and caused no significant phytotoxicity of crops tested. Fortress had 100% control of bittercress and oxalis 30 and 60 days after treatment (DAT) and significantly better control than other treatments 90 DAT. Fortress controlled eclipta well 30 and 60 DAT. It provided 97.5% to 99.4% control of spurge 30 DAT but almost none 90 DAT. Fortress provided 75% to 76.9% phyllanthus control 60 DAT while Snapshot provided 91.4% control. All herbicide treatments provided at least 90.5% crabgrass control 90 DAT. Fortress had no effect on size index and caused no significant phytotoxicity of the crops tested. In another experiment, #1 containers filled with amended 6 pine bark : 1 sand substrate were treated with Fortress (isoxaben + dithiopyr) at 100, 150, and 200 lbs/A, Freehand® (dimethenamid-P + pendimethalin), Gemini® (prodiamine + isoxaben), and Snapshot (isoxaben + trifluralin) and then overseeded with 25 seeds of either oxalis, bittercress, eclipta, phyllanthus, spurge, or crabgrass. All herbicide treatments provided at least 95.5% control on oxalis 30, 60, and 90 DAT. Fortress at all rates provided better control than Freehand and Snapshot 120 DAT. Overall, Fortress provided similar bittercress control compared to Snapshot and Gemini, and better control than Freehand. While Fortress at 200 lbs/A provided similar spurge control compared to Snapshot up to 90 DAT, all Fortress provided better spurge control than Snapshot 120 DAT. Fortress at 150 lbs/A provided similar eclipta control compared to Snapshot, while Fortress at 200 lbs/A provided better eclipta control than most treatments. Overall, Fortress at 150 lbs/A provided similar phyllanthus control compared to Snapshot, while Fortress at 200 lbs/A provided better phyllanthus control than all other herbicide treatments.