Field Control of the Fladiolus Thrips (Taeniothrips Giadioli M. & S.)

Abstract

Paris green-brown sugar spray, a lead arsenate combination spray, and nicotine tannate. as well as three other sprays, were tested, each on 15 small plots during the 1932 season (8 applications at weekly intervals). Each small plot contained two red varieties of gladiolus, Crimson Glow and Brilliant, which had been uniformly infested with the gladiolus thrips. Paris green-brown sugar spray was by far the most efficient, not only in controlling the thrips, but also in reducing thrips injury to the flowers. Data on the number and size of flowers, foliage development, and number and size of corms harvested indicated that the pine tar oil-nicotine spray, as well as the nicotine sulfate-soap spray, especially the latter, had a distinctly injurious effect on the plants. Of the five other insecticides that were tested on a smaller scale at this same field, the white oil-nicotine spray was most effective, but this did not approach the Paris green-brown sugar spray in efficiency. A total of 14 insecticides, including all the above, were tested at another field for their effect on uninfested gladiolus (variety Alice Tiplady). Only the nicotine sulfate-soap spray had any distinctly injurious effect (as evidenced by flower and corm production). Preliminary experiments indicated that one or two applications of naphthalene, paradichlorobenzene, tobacco dust, carbon disulphide emulsion, or ethylene dichloride emulsion, applied to the soil just after planting corms, would not be effective for controlling the thrips. Naphthalene and paradichlorobenzene (especially the latter) greatly retarded the growth of the plants and evidently caused some reduction in the corm and flower production. The gladiolus thrips does not appear to move about much during the growing and early blooming season, but considerable numbers do migrate, apparently close to the ground, after the flowers are cut. Muslin barriers 3 feet high erected between treated plots were apparently effective up through flowering time in reducing any slight movement of thrips from one plot to another. Observations of the predator Orius insidiosus (Say) indicated that it can kill as many as 30 thrips per day and that it might reduce thrips populations in small isolated plots.