Efficacy, Phytotoxicity, and Cover Crop Response of Herbicide Combinations in Dark Fire Cured Tobacco
Field studies were established during the summer of 1999 at the Agricultural Research and Education Complex of Western Kentucky University to evaluate efficacy, phytotoxicity, and cover crop response of herbicide combinations in dark fire cured tobacco. A randomized complete block design was used with nine treatments replicated three times. Hydroponic tobacco transplants (c.v. 'TND950') were established on May 20,1999 in a conventionally tilled system on a Pembroke silt loam (Mollic Palleudalf) with a pH of 5.8 and an organic matter content of 1.2%. The transplants were established at a population of approximately 10,278 plants/ha. Herbicide treatments were applied on May 19, 1999 with a CO2 backpack sprayer. Sulfentrazone as Spartan 75DF was applied in all nine treatments at a rate of 0.47 kg pr/ha. Six of the nine treatments included various rates of clomazone as Command 3ME. Two of the nine treatments included napropamide as Devrinol 50DF. Visual evaluations of crop phytotoxicity due to herbicide application were recorded at 21 and 44 days after treatment (DAT). Weed control was evaluated at 21, 29, 44, and 58 DAT for the following species: Ipomoea hederacea L. (Ivyleaf morningglory), Amaranthus hybridus L. (smooth pigweed), and Eleusine indica L. (goosegrass). Crop injury and weed control evaluations were recorded on a 0-100% scale with 0 representing no injury and/or no control and 100 representing plant death. After crop removal, two types of tillage were performed to examine wheat injury effects due to tillage. One subplot was moldboard plowed and disked while the other subplot was disked. Following tillage operations, winter wheat (Triticum aestivum) was planted on October 30,1999 at a rate of 134.68 kg pr/ha. Visual wheat chlorosis evaluations of each subplot were recorded and based on a scale of 0-100%. Stand counts were taken in the subplots to examine stand loss due to treatment. Wheat aboveground biomass was harvested from each subplot to evaluate the relationship between wheat growth and herbicide rate. Sulfentrazone alone provided >66% control of Eleusine indica, >96% control of Ipomoea hederacea, and >88% of Amaranthus hybridus at all evaluation dates. When combined with 0.584 L pr/ha clomazone, sulfentrazone provided >82% control of all weed species 58 DAT. Sulfentrazone combined with > 1.17 L pr/ha clomazone provided > 86% Eleusine indica control, >60% Ipomoea hederacea control, and >84% Amaranthus hybridus control. Sulfentrazone combined with 1.12 kg pr/ha napropamide provided >71% control for all weed species at all evaluation dates. However, sulfentrazone plus 2.24 kg pr/ha napropamide provided only >55% control of species at all evaluation dates. Wheat chlorosis was affected by increased rates of clomazone combined with sulfentrazone at both 25 and 41 DAP (days after planting). Fresh weight also exhibited a trend of decreased mass as clomazone application rate increased. Addition of >1.75 L pr/ha clomazone decreased stand count at both evaluation dates, as compared to the sulfentrazone treatment. There were no differences in stand count between napropamide rates in either stand count evaluation. Wheat chlorosis 25 and 41 DAP was greater in plots that were not moldboard plowed. Areas moldboard plowed and disked exhibited less chlorosis, but tillage had no significant effect on wheat biomass or stand count.
Networked Digital Library of Theses and Dissertations