Graduate Thesis Or Dissertation
 

Population dynamics, distribution, and control of nematodes in highbush blueberries

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  • Fluctuations in population density of Pratylenchus sp., Trichodorus sp., and Xiphinema americanum s. 1. in three blueberry fields were determined monthly for one year. Pratylenchus densities were greatest in August and least in October. Three distinct periods of population growth occurred; during January, April, and between June and August. Trichodorus populations were highest between February and April, and lowest in June. Xiphinema occurred in only one of three fields sampled, with densities highest in May and lowest in August. Root samples from blueberry plants, and soil samples from the rooting zone were taken in June of 1986 to determine horizontal and vertical distribution of Pratylenchus and Trichodorus populations. Samples were taken at depths of 0-3, 3-9, and 9-15 inches at 6-18 and 18-30 inches from the base of the plant and within and between rows. Pratylenchus densities at certain orientations depended on the distance from the base of the plant that the soil was sampled. Samples taken within the row were similar at one and two feet from the base of the plant, whereas samples from between rows taken at one foot from the base of the plant were significantly less (22%, p< .10) than those taken from two feet away. The presence of a living mulch between the rows may account for this difference. Pratylenchus populations differed significantly with depth. There was little difference in density between 3-9 inches and 9-15 inches, but both differed significantly (p<0.01) from 0-3 inches. Densities were greatest below 3 inches. Trichodorus densities depended on the distance the sample was taken from the base of the plant. At one foot from the base of the plant, the population was significantly greater (p< .01) than at two feet. The horizontal distribution of Pratylenchus and Trichodorus in a blueberry field was determined by sampling five rows of ten plants each, at a depth of 3-9 inches. Pratylenchus populations tended to be distributed in a clumped pattern. The mean population density of 50 samples was 270 Pratylenchus/ qt. soil and 42% of the 50 plants sampled were infested. In contrast, Trichodorus distribution was fairly uniform, with 74% of the 50 plants infested. The mean population was 253 Trichodorus /qt. soil. Efficacy trials with fenamiphos (Nemacur 3E) indicated that the most effective rate for Pratylenchus control was 12 lbs. ai/A, which reduced populations by 95%. Fenamiphos was not an effective control for Trichodorus in this study. Analysis of fenamiphos treated fruit from two Oregon and one Washington blueberry fields showed no detectable chemical residues for 6 or 12 ai/A rates at the spiking level of 0.1 ppm.
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Déclaration de droits
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