Graduate Thesis Or Dissertation
 

Competitive effects and control of weeds in winter wheat on the Anatolian Plateau, Turkey

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/n009w542x

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  • Wheat is the major crop produced on the Anatolian Plateau of Turkey. Annual weeds cause large yields reductions in the wheat crop. Several formulations of 2, 4-D and mixtures of 2, 4-D and 2,4, 5-T are the only materials currently available for use in Turkey on wheat. The objective of this study was to determine the optimum time for application of herbicides in order to reduce competition between winter wheat (Triticum aestivum cv. 'Bolal') and annual weeds. Several herbicides and herbicide mixtures were compared for their effectiveness against two major weed species, yellowweed (Boreava orientalis L.) and cornflower (Centaurea cyanus L. ). Herbicides were applied at three different dates according to growth stages of wheat and weeds. Two series of handweeded plots were also included. One set allowed weed competition with the wheat for 4 and 8 weeks and was handweeded for the remainder of the season. The other set was kept free of weeds for 4 and 8 weeks and left weedy for the remainder of the season. Weed-free and weedy control plots were included. Wheat which was free from weed competition in the early part of the growing season produced the highest yields. Plots on which herbicides were applied at the earliest date produced higher yields than where herbicides were applied later. Optimum time for herbicide application was when wheat was in the two to three tiller stage and weeds were small, five to six leaf stage. Delaying the application of herbicides beyond the critical period of competition, which is determined by stage of growth of weeds and wheat, resulted in a continuing decrease in wheat yields. Chemicals which produced satisfactory weed control and increased wheat yields were, 2,4-D, 2,4-D + 2,4,5-T, bromoxynil + MCPA, and terbutryn + 2,4-D combinations. The terbutryn + 2,4-D combination needs further research because of possible phytotoxicity to wheat. It was concluded that using only herbicides now available in Turkey, wheat yield increases of 25 to 50% or more are possible by applying herbicides at the optimum time.
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