Differential Cucurbita spp. Tolerance to the Herbicide Trifluralin

Abstract

Abstract A germination test of seven Cucurbita entries in a dark growth chamber indicated no effects of trifluralin on germination. Increasing the plant population/pot of butternut type squash (C. moschata Poir, cv. Ponca) did not improve trifluralin tolerance. A factorial arrangement of three treatments (six Cucurbita entries × five trifluralin doses × three herbicide incorporation zone placements in pots) with a randomized complete block design was used in two greenhouse experiments. The incorporation zone treatments included surface layering (above seed), subsurface layering (below seed), and full-pot incorporation of the herbicide dose. The layering treatments increased concentration (ppm) of the herbicide due to the concentrated dose in a small volume of sand medium (200 vs. 500 g quartz sand). Total plant dry weight differences were detected between zoning treatments. After an initial stimulating effect, plant dry weight decreased over the dose range. The C. maxima Duch, PI 182202, and C. pepo L., PI 234252, showed the highest tolerance. Adventitious roots developed and senescence of the primary root occurred above the subsurface treated layer that had been treated at high trifluralin concentrations. The root zone was the primary site of herbicide action. C. moschata, C. pepo, and C. maxima spp. (21 entries) were screened in two tests for tolerance to trifluralin over a range of 0 to 0.4 ppm incorporated in quartz sand. Entry, herbicide dose, and entry × dose interaction effects were significant. C. maxima PI lines 368567 and 179264 exhibited the highest tolerance regardless of dose. Chemical name used: α,α,α-trifluoro-2,6-dinitro-N, N-dipropyl-p-toluidine (trifluralin).