Graduate Thesis Or Dissertation

Effects of tillage on emergence of mint root borer, Fumibotys fumalis Guenée, and on other agronomic factors in peppermint, Mentha piperita L.

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  • Studies were conducted in the Willamette Valley of western Oregon to evaluate the effects of plowing (7.5-15 cm deep) and disking (5-10 cm deep) in peppermint, Mentha piperita L., on the following factors: 1) emergence of adult "mint root borer", Fumibotys fumalis Guenée; 2) suppression of common groundsel, Senecio vulgaris L.; 3) spread of Verticillium wilt, Verticillium dahliae Kleb.; 4) soil chemical factors such as pH and nutrient elements; and 5) peppermint growth, yield, and oil quality and maturity. Plowing and disking significantly reduced emergence of adult f. fumalis. In all treatments adult emergence peaked from early July to early August. Female emergence peaked about one week later than for males in two test plots. Populations of immature F. fumalis were aggregated, and were not significantly correlated with populations of adults. In one test plot, plowing significantly reduced the density, dry weight biomass, and plant vigor of S. vulgaris. Even though plowing reduced the density of S. vulgaris in other test plots, neither the dry weight biomass nor plant vigor were reduced. Disking reduced stands of S. vulgaris to a limited extent. Plowing significantly reduced false dandelion, Hypochaeris radicata L., by about 65 percent in one test plot. Plowing or disking did not affect the number or percentage of plants showing typical symptoms of Verticillium wilt. However, Verticillium wilt was aggregated within test plots so the influence of tillage on the spread of VerticiIIium wilt is uncertain. Plowing resulted in a more uniform distribution of pH and nutrients throughout the 0-15 cm soil layer. Plowed plots had higher levels of pH and Ca in the surface 0-5 cm of soil, and higher levels of P and K in 5-15 cm of soil. In disked plots, levels of pH, P, and K in 0-5 cm and 5-15 cm sail samples were intermediate between plowed and until led plots. Tillage treatments did not significantly affect levels of Mg or B. Density of peppermint plants was lower in plowed and disked plots than in untilled plots. Peppermint plant viqor was higher in tilled than untilled treatments at one test location, resulting in higher peppermint hay and oil yields. Peppermint hay and oil yields at other test locations were generally not affected by tillage treatments. Analysis of selected terpene compounds from oil samples indicated that plowing or disking did not affect peppermint oil quality, but may have delayed the process of oil maturation. Plowed plots had a significantly greater percentage (ca. 14%) of total rhizome dry weight in 5-15 cm of soil than in disked or untilled plots.
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