Effect of environment on plant response to DPX-PE350 [sodium 2-chloro-6-(4,5-dimethoxy-pyrimidin-2-ylthio)benzoate]

Environmental conditions at the time of spraying can affect the activity of foliar-applied herbicides. Evaluation of environmental effect on experimental herbicides is one important area of research. DPX-PE350 is a potential cotton herbicide for postemergence broadleaf weed control.

Greenhouse and growth chamber studies were conducted to determine the DPX-PE350 rate causing 50% growth reduction (GR₅₀) in cotton (Gossypium hirsutum L.), velvetleaf (Abutilon theophrasti) and sicklepod (Cassia obtusifolia), the effect of time until rainfall on DPX-PE350 activity on velvetleaf, and the effect of soil moisture on root uptake from foliar-applied DPX-PE350. Additional experiments were conducted with formulated and radiolabeled DPX-PE350 to determine the effect of soil moisture and ambient temperature on DPX-PE350 activity on cotton and velvetleaf.

In whole-plant studies, data were collected 2 to 4 wk after treatment (WAT). Foliar chlorosis and stunting were visually evaluated, and plant heights and/or fresh weights were recorded. In ¹⁴C experiments, absorption and translocation were measured 6, 24, and 72 h after treatment With ¹⁴C-DPX-PE350. ¹⁴C was detected with liquid scintillation spectroscopy.

Velvetleaf GR₅₀ at 2 WAT occurred with DPX-PE350 at 70 g ai ha^-1. A GR₅₀ for sicklepod and cotton was not observed at the examined rates because of high tolerance to DPX-PE350.

Velvetleaf injury was greatest when 5 h lapsed before a 5 mm simulated rainfall event. Injury was observed when 0.08 h lapsed before the rainfall event, possibly because DPX-PE350 moved from foliage into the soil where uptake by plant roots could occur.

DPX-PE350 applied to velvetleaf foliage accounted for most injury, although root uptake contributed to herbicide activity at -0.03 MPa soil moisture. Velvetleaf injury was greatest when DPX-PE350 was applied to plants growing at soil moistures of -0.03 MPa compared to -1 MPa, and when DPX-PE350 was applied simultaneously to foliage and soil.

DPX-PE350 injury to cotton was <20% 2 WAT on plants grown at 25/23, 30/28, or 35/33 C, at soil moistures of -0.03, -0.5, or -1 MPa. DPX-PE350 injured velvetleaf less at lower soil moistures.

Cotton and velvetleaf absorbed more ¹⁴C-DPX-PE350 at 30/28 or 35/33 C than at 25/23 C. Cotton absorbed more herbicide than velvetleaf at all temperatures and soil moistures but translocated <3% of absorbed material. At warmer temperatures, velvetleaf absorbed and translocated less ¹⁴C when soil was dry (-1.0 MPa) than when plants were watered to field capacity (-0.03 MPa). This decrease in absorption and translocation may partially explain reduced DPX-PE350 activity on velvetleaf growing in dry soil.