Thesis (doctoral)--University of Belgrade, 1967. / At head of title: Institut za tutun--Prilep. Summary in English. Errata leaf inserted. Includes bibliographical references (p. 118-121).

Very high infestation levels of Thrips tabaci Lindeman were observed on onions at Ste-Clotilde (Quebec) with seasonal means of 149 and 161 thrips/plant for 1988 and 1989 respectively. No significant differences in thrips densities were detected among six yellow onion cultivars (Capable, Flame, Norstar, Progress, Rocket, Taurus) through weekly comparisons in 1988 and biweekly comparisons in 1989. / A new variable, the cumulative number of thrips-days/plant, was used to model the impact of T. tabaci on onion yields. This variable allowed for better-fitted models, especially in 1989 where greater variability of the onion yields was observed. A modified Gompertz equation gave the best fit for 1988. No yield reduction due to T. tabaci was observed up to the 1000 cumulative thrips-days/plant point, beyond which the thrips impact first increased with the feeding pressure and then gradually decreased to a minimal level corresponding to a yield loss of 43%. In 1989, thrips impact was immediate and best described by an exponential model with a maximal yield loss of 34,5%. / Economic thresholds of 964 and 251 cumulative thrips-days/plant were calculated for 1988 and 1989 respectively. Converted to thrips/leaf these correspond to 2,2 and 0,9 thrips/leaf. This conversion could facilitate their use in a field situation. / Spatial distribution of T. tabaci was analyzed in ten commercial onion fields. Within field, density was homogeneous in the majority of cases. In some fields, higher thrips densities were temporary (two consecutive weeks at most) in one or two field margins. / The Iwao method was used to calculate the acceptance boundaries of sequential sampling plans for the economic thresholds of 0,9 and 2,2 thrips/leaf and onion growth stages of 6, 7, 8, 9 and 10 green leaves. (Abstract shortened by UMI.)

No description available.

Onion thrips (Thrips tabaci) and Iris Yellow Spot Virus (IYSV) constitute a pest complex of global concern for allium growers. Yield losses due to onion thrips alone can be heavy, and in tandem with IYSV, these losses can be complete. This study was one phase of a multi-phase research project intent on exploring the potential drivers of thrips and virus infestation in onion. Preliminary observations in participating growers’ fields in northern Utah pointed towards a potential link between weedy field borders and thrips/IYSV infestation in onion. Field work was carried out at the Kaysville experiment station examining the possible relationships between thrips and IYSV incidence in onion and the presence of adjacent weed populations. This research was conducted with the intent of guiding growers’ decisions regarding field border management, and to provide additional insights into onion thrips behavior. While implications for growers remain unclear, thrips preferences regarding host plant utilization were identified, as well as preliminary evidence of additional plant species capable of hosting IYSV.