Fertilizer Placement and Herbicide Rate Affect Weed Control and Crop Growth in Containers

Abstract

Abstract Three experiments were conducted in Oregon and Mississippi to evaluate the effect of fertilizer placement and rate of herbicide application on weed control and crop growth. In Expt. 1, Osmocote 18N–2.6P–10.0K (18–6–12) controlled release fertilizer (CRF) was applied at 12 g (0.4 oz) per container (#1) either topdressed, incorporated, or dibbled (placed under the liner prior to potting); and OH2 (pendimethalin + oxyfluorfen) was applied at 0, 28, 56, or 112 kg/ha (0, 25, 50, or 100 lbs/A). Containers were overseeded with common groundsel (Senecio vulgaris). In Expt. 2, Osmocote 17N–3.0P–10.1K (17–7–12) CRF was applied at 18 g (0.6 oz) per container using the same placement methods as Expt. 1; and Rout (oryzalin + oxyfluorfen) was applied at 0, 28, 56, or 112 kg/ha (0, 25, 50, or 100 lbs/A). A hand-weeded check was also included, and containers were overseeded with prostrate spurge (Chamaesyce prostrata). In Expt. 3, containers were fertilized with either 12 g (0.4 oz) of Apex 20N–4.3P–8.4K (20–10–10) CRF or 14 g (0.5 oz) of Apex 17N–2.2P–9.2K (17–5–11) CRF using similar fertilizer placement methods; and Snapshot 2.5TG (isoxaben + trifluralin) was applied at 0, 84, or 168 kg/ha (0, 75, or 150 lb/A). Containers were overseeded with creeping woodsorrel (Oxalis corniculata). Weed control improved with increasing herbicide rate. Across the three experiments, dibbling CRFs with no herbicide resulted in 85 to 97% weed control, while topdressing resulted in 19 to 85% and incorporating resulted in 55 to 88% control. With herbicides, dibbling fertilizer resulted in 89 to 99% weed control while topdressing resulted in 82 to 90% and incorporating 81 to 98%. Dibbling fertilizer resulted in greater shoot growth (growth index) of azalea (Rhododendron ‘Stewartsonian’), holly (Ilex crenata ‘Compacta’), lavender (Lavandula × intermedia ‘Grosso’), and wintercreeper euonymus (Euonymus fortunei ‘Emerald Gaiety’). In Expt. 3, incorporating CRFs resulted in higher root ratings than dibbling in lavender and euonymus. Though measurable differences in root and shoot growth were observed in all experiments, differences were economically unimportant.