Doctoral Dissertations

Date of Award

8-1993

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plant, Soil and Environmental Sciences

Major Professor

Robert M. Hayes

Committee Members

Thomas C. Mueller, William Krueger, Otto Schwarz, Don Tyler

Abstract

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.

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