Effect of Living and Straw Mulch in Integration with Reduced Doses of Trifluralin on Yield and Yield Components of Dill (Anethum graveolens L.)

Integrated weed control in medicinal plants is one of the most important components of sustainable production. The dill seed production could be affected mainly by weed interference because of low competitive ability of this medicinal plant against weeds. So, this study was conducted in order to evaluate the effect of different doses of trifluralin in integration with non-chemical weed control options including living mulch, straw mulch and one time hand weeding on weeds, yield components, grain and essential oil production of dill.

 The study was conducted in Research Field of Agriculture-Jahad in Khoda Afarin County in East Azarbaijan Iran in 2019 as factorial experiment based on randomized complete block design with three replications. The first factor was application of different rates of trifluralin at four levels including 0, 480, 720 and 960 g ai ha-1 of trifluralin herbicide and the second factor was different levels of non-chemical weed control consisted of planting the living mulch of fenugreek (Trigonella foenum-graecum L.), planting the living mulch of bitter vetch (Vicia ervilla L.), application of wheat straw mulch, one time hand weeding 50 days after emergence of dill and control (without non-chemical weed control). Also the weed-free treatment during whole growth season was considered in the experiment.

The results indicated that the interaction effect of herbicide dose × non-chemical weed control method was significant (p ≤ 0.01) on weed density and biomass. At all non-chemical control levels, increasing the trifluralin dose reduced the weed density and the lowest weed density (2.33 Plant m-2) was observed in one time hand weeding and straw mulch treatments. The weed density at all non-chemical control levels decreased compared with that in without non-chemical control. Increasing the trifluralin dose decreased the weed biomass at all non-chemical control levels, and the lowest weed biomass was observed in one time hand weeding treatment + 960 g ai ha-1 of trifluralin (78 g m-2) that caused 86% reduction in weed biomass compared with control treatment. At all non-chemical control levels, the weed biomass decreased compared with that in without non-chemical control. Comparison of weed biomass among the different mulch treatments indicated that except in control (0 g ai ha-1 of trifluralin), the weed biomasses were not significantly different under all herbicide doses. The effect of non-chemical control level was significant on plant height, number of umbels per plant and 1000-grain weight of dill. The means comparison indicated that among the non-chemical weed control treatments the greatest plant height (97 cm), number of umbels per plant (31.8) and 1000-grain weight (192.8 g) were obtained in wheat straw mulch application. Also increasing the herbicide dose, improved the number of umbels per plant and 1000-grain weight of dill as the highest values were observed in 960 g ai ha-1 of trifluralin. The interaction effect of herbicide dose × non-chemical weed control method was significant on grain number per plant and grain yield of dill. At all non-chemical control levels, the grain number per plant enhanced by increasing the trifluralin dose. Comparing the non-chemical control treatment showed that the highest grain number per plant was observed in straw mulch application treatment and other non-chemical weed control treatments were not significantly different. The all non-chemical weed control treatments increased the grain number per plant compared with that in control treatment. By increasing the trifluralin dose under all non-chemical control treatments the grain yield of dill enhanced. Also the grain yield increased significantly at all non-chemical control treatments compared with those in without non-chemical control and the greatest grain yield of dill was observed in straw mulch application treatment + 960 g ai ha-1 of trifluralin (9842 kg ha-1) that indicated 6% reduction compared with weed free treatment. Also the grain yield in this treatment increased by 89.7% compared with that in without control and 0 g ai ha-1 of trifluralin (weed-infested treatment). The grain yield of dill in one time hand weeding treatment was higher than those in fenugreek and bitter vetch living mulch treatments. Also in living mulch treatments there were no significant difference between dill grain yield of 480 and 720 g ai ha-1 of trifluralin. The effects of herbicide dose and non-chemical weed control treatment were significant on essential oil content and yield of dill. The essential oil content and yield increased by increasing the herbicide dose and the highest essential oil content (1.46%) and yield (110.34 kg ha-1) were observed in 960 g ai ha-1 of trifluralin. The essential oil content and yield incresead at all non-chemical control treatments compared with that in without control treatment. The highest essential oil content (1.38%) was obtained in straw mulch treatment that was not significantly different with that in one time hand weeding (1.35%) treatment. The highest essential oil yield (100.6 kg ha-1) was obtained in straw mulc treatment that was not significantly different with that in one time hand weeding (96.43 kg ha-1).

 The all non-chemical weed control treatments decreased the weed density and biomass but the hand weeding and straw mulch treatments showed higher efficacy in weed biomass reduction compared with living mulch treatments (fenugreek and bitter vetch). The grain and essential oil production of dill in straw mulch and one time hand weeding treatments were greater than those in fenugreek and bitter vetch living mulch treatments. Therefore, the straw mulch and one time hand weeding could be recommended in integration with reduced doses of trfluralin for sustainable weed management of dill.