Influence of reduced rates and split application of herbicides on weed control and on yield in carrots (Daucus carota L.)

摘要

Studies were conducted to evaluate the efficacy of different application methods using reduced rates of herbicides as well as to determine the possibility of decreasing total herbicide input. Trials were carried out from 1994 to 1996 at Skierniewice on a pseudo-podzolic soil (lesive) build up of sandy deposits on boulder loam, containing 1.2-1.5% of organic matter. Weed control programmes tested in the experiments were based on reduced rates of pre-emergence herbicides followed by low rates of linuron applied early post-emergent as a single or a split application. In the experiments conducted the complete rates of linuron and flurochloridone applied pre-emergently were 0.75 kg centre dot ha~(-1) and 0.6 kg centre dot ha~(-1), whereas the reduced rates - 0.375 kg centre dot ha~(-1) and 0.3-0.4 kg centre dot ha~(-1), respectively. Early post-emergence sprayings were executed exclusively with linuron, either in single applications at i to 2-leaf stage Of carrot (0.25 or 0.375 kg centre dot ha~(-1)) or split applications at cotyledone stage and 10-14 days later (0.19 + 0.19 kg centre dot ha~(-1) or 0.19 + 0.5 kg ha~(-1)). The effect of diquat (0.6 kg centre dot ha~(-1)) applied before carrot emergence, followed by an early post-emergence split application of linuron (0.25 + 0.25 kg centre dot ha~(-1) or 0.25 + 0.5 kg centre dot ha~(-1)) was investigated too. The effect of reduced dose rates of herbicides was compared to that of the standard doses of pre-emergence ones. The results of experiments revealed that even lowest herbicide rates have given acceptable weed destruction but higher ones were more effective and often resulted in complete control. Dose rates of linuron and flurochloridone applied pre-emergently can be diminished by up to 50%. The weed control programme based on pre-emergence application of flurochloridone at low rates, followed by an early post-emergence split application of linuron was the most effective one. No phytotoxicity symptoms were observed on carrots even after post-emergence applications at early growth stages. The yields from herbicide treated plots were significantly higher than that from untreated plots. In contrast, the differences between yields coming from plots treated with high and low herbicide rates were not significant.