The Study Efficiency of Reduced Rate of Pendimethalin Integrated with Mulch and Hand-Weeding in Fennel (Foeniculum vulgare Mill.).

Introduction: Fennel has been cultivated as a medicinal and spice plant for a long time in different areas of Iran. However, its characterizes such as slow-growing, weak establishment, owning low LAI index and long seasonal plant, make it a poor competitor against weed, therefore, protection from weed is essential for successful cropping. The combination of management practices, such as mulching with herbicide could improve weed control efficacy of reduced rates. Limited information is available on control of weeds in fennel as important medicinal plant. Using a combination of physical control and herbicides at reduced rate may increase the efficacy of both treatments while reducing the cost of the weed control program and environmental impact of over reliance on herbicide applications. Therefore, the objective of this study was to evaluate the effects of reduced rates of the pendimethalin alone and in combination with wheat straw mulch and one hand-weeding on the growth of weed and grain yield of cultivated fennel. Materials and Methods: this experiment was carried out at the Research Farm of Faculty of Agriculture, University of Zanjan in the spring 2012 to introduce an integrated weed control method in fennel. In this experiment the efficacy of different rates of pendimethalin alone and with combination with one hand weeding and straw mulch for selective control of grass and broadleaf weed species were evaluated. Field experiment was laid out as factorial based on randomized complete block design with three replications. Factors were application dose (0, 660, 990 and 1320 g a.i. ha-1) and supplemental weed control (none, one hand-weeding, mulching). A plot with whole season hand weeding was also included as control. The recommended doses of pendimethalin were 1320 g ai ha-1. Fennel was planted at 10 seeds m-2, at 0.5 m row spacing, on May 6, 2012. Pendimethalin was applied pre-emergence soon after planting. In the mulch treatments, wheat straw were spread evenly after fennel planting at the rate of 2 kg m-2. In the weed control treatments which one hand weeding used as supplemental physical control, a hand-weeding was performed at 50 days after planting. At fennel maturity, weeds were harvested from a 0.5 m2 area and dried in an oven for 48 h at 75 oC and biomass was recorded. For assessing the effect of the treatments on fennel seed yield a 2 m2 centre area of the plots was harvested manually. Data were subjected to an analysis of variance using PROC GLM in SAS Software. The means were compared using a Fisher's Protected Least Significance Difference test (P< 0.05). Results and Discussion: Biomass of broad leaf weeds was significantly affected by herbicide doses and supplemental control. However, application dose and supplemental control interaction were not significant on broad leaf weeds biomass. Maximum broadleaf weed biomass control (85.9%) was recorded by recommended dose of pendimethalin. For a given dose of herbicide, weed control efficiency was higher when the physical methods were used as supplemental control and generally one hand-weeding was effective than mulching. All weed management treatments reduced biomass of grass weeds compared to weedy control. No differences were observed between the grass weed biomass in plots which received 75% and 100% of the labeled recommended rate of pendimethalin. Significant differences (p < 0.05) among herbicide rates and 50% of the labeled recommended rate (660 g a.i. ha-1) was observed for grass weed biomass. Biomass of grass weeds was also significantly affected by physical control. Maximum grass weed control (86%) was observed with one hand-weeding than the mulch. Same to broadleaf, the interaction effect of application dose × supplemental control treatments was not significant for grass weeds biomass. Total weeds biomass was significantly affected by herbicide. The interaction effect of application dose × supplemental control treatments were significant for total weeds biomass. Maximum weed biomass (1837.5 g.m-2) was recorded in weedy control. When herbicide combined with one hand-weeding, the rate of 660 g a.i. ha-1 of pendimethalin was sufficient to provide 81% total weed control, which was statistically similar to the best control achieved for all dose and physical combination treatments. Fennel seed yield and yield component was significantly affected by application dose and physical control. The greatest seed yield loss (97.6%) was recorded in no weed control plots. and the lowest seed yield loss (13%) was seen in the recommended dose of pendimethalin + one hand-weeding plot. When one hand-weeding was used as a supplemental control, increased herbicide application rates from 990 to 1320 g a.i. ha-1 did not significantly influence the level of fennel seed yield. Conclusions Overall, results of this study showed that pendimethalin in labeled recommended rate and applied alone was not sufficient to provide season long weed control. The recommended dose in combination with one hand weeding could not prevent of economic yield loss. As a result, it is recommended to test efficient herbicide or other methods of weed management of this plant. To improve the level of weed control with mulch, application of herbicides at the same time as the mulch or supplemental hand-weeding could be suggested as a part of integrated weed management in fennel.