The effect of reduced growth retardant rates on weed infestation of a winter wheat (Triticum aestivum L.) crop.

In Poland, like in other countries of the world, cereals have a dominant position in the crop production structure, especially winter wheat. Cereals, in particular winter varieties, are prone to heavy weed infestation, both with dicotyledonous and monocotyledonous species. Therefore, weed management is one of important factors that affect yields of cereals and as a consequence the profitability of cereal growing. The present study investigated the effect of full and reduced rates of three growth retardants with different active ingredients (chlormequat chloride (CC), trinexapac-ethyl (TE), and chlormequat chloride (CC) + ethephon (E)), used in combination with an adjuvant or without adjuvant, on the quantitative parameters of weed infestation and weed biodiversity in a winter wheat crop. Plots where no growth retardants were used were the control treatment. The level of weed infestation of the winter wheat crop, as measured by the number and air-dry weight of weeds, was significantly differentiated by weather conditions, year and growth regulator rates. The study results show that growth retardant rates can be reduced in winter wheat growing without the risk of increased weed infestation. Chlormequat chloride + ethephon and trinexapac-ethyl showed the highest effectiveness in reducing weed infestation. The study found a positive trend towards reducing the number and weight of weeds under the influence of the adjuvant used (oil SN 76%). But this agent only slightly affected the species composition and constancy of the weed community. The dominant species in the winter wheat crop were Chenopodium album, Veronica persica and Viola arvensis, which were placed in constancy class IV. The lower the retardant rate applied, the more their numbers decreased, whereas the number of other weed species were generally reduced by standard rates of weed control agents.