DIFFERENT RESPONSES OF WINTER-WHEAT CULTI VARS TO CHLORTOLURON

Effects of three formulations of the chlortoluron active ingredient an d several combined products also containing this agent on the growth a nd development of winter wheat were studied in small-plot field experi ments. Effects on a number of tillers and dry matter production per un it area and grain yield in sets of eight and nine winter wheat varieti es were investigated in 1991/1992, 1992/1993 and 1993/1994. The result s obtained in 1991/1992 showed that pre-emergent and post-emergent app lication of herbicides which contained chlortoluron as one of effectiv e agents to the Hana variety caused reduction of plant weight in all c ases studied. Significant reduction was recorded after the pre-emergen t application of Syntop, Assert + chlortoluron and a combination of Di curan 80 WP + Aminex. In 1992/1993, the pre-emergent autumn applicatio n of Pendiron and post-emergent spring one of three formulations of ch lortoluron were investigated in a set of nine winter wheat varieties. Pendiron showed phytotoxicity expressed in considerable growth hinderi ng. A number of tilters was lower in all varieties when compared to a check variety, and significantly lower in Vega and Torysa varieties in which grain yield was also significantly reduced. Significant yield r eduction was determined in Livia too. Bt three chlortoluron formulatio ns in spring post-emergent application significant yield loss was asse ssed in Vega and Torysa. In 1993/1994, responses of nine winter wheat varieties to the post-emergent autumn application with chlortoluron co ntained in three commercial products were studied. The varieties Vega, Bruta and Sida showed significant reduction of a tiller number after all of the products applied. Dry matter yield per unit area was reduce d in all varieties studied, and significantly reduced in Vega, Bruta a nd Sida after all products. In the varieties Asta, Siria, Danita and S imona - after the products which are marked with asterisks (Fig. 4). G rain yield was significantly lower in Vega. Based on statistical evalu ation, the application of chlortoluron can be considered as a measure which could cause the reduction of production ability, including yield loss in sensitive varieties. That can be increased in fields which do not enable higher compensation of a lower tiller number and biomass d ry matter at early growth and developmental stages. Despite high yield potential, the varieties Vega, Bruta, Torysa and Sida were sensitive.