Feasibility of Chemical Control of Weeds in Cumin (Cuminum cyminum L.)

Cumin (Cuminum cyminum L.) is one of the most important domestic medicinal plants in the country. Currently Iran is one of the most important producers of cumin. Features such as short growing season, low water requirement, lack of interference with other crops, high economic justification for other crops and exportability, make this plant a special place in the pattern of cultivated area This plant has a special place in the cultivation pattern of arid and semi-arid regions, including Khorasan. Given that cumin is a delicate plant with low weed competitiveness and on the other hand because it leaves cover the ground as much as possible, it provides a suitable environment for weed growth and development. Although cumin growers are currently struggling with weeding the fields mechanically, this method is costly and damages to the cushion bushes, identifying the herbicide of choice for combating weeds. The weeds of this plant will be a great step towards reducing the cost of its production. Therefore, the purpose of this study was to evaluate the chemical control of weeds and to evaluate the cumin tolerance to herbicides and to select herbicides for this important medicinal plant.

In order to evaluate the efficacy of herbicides from cell division inhibitor and photosystem II inhibitor groups, an experiment was conducted as a randomized complete block design with 6 treatments and 3 replications in Agricultural Research Farm at University of Birjand 2017. In this research herbicides from cell division inhibitors group including trifluralin pre-plant incorporated (2 L.ha-1), pendimethalin pre-plant incorporated (3 L.ha-1), pendimethalin preemergence (3 L.ha-1) as well as herbicides from photosystem II inhibitors group including prometryn preemergence (2 Kg.h-1), metribuzin preemergence (1 Kg.h-1) and a weeding treatment was also added. The measured traits for weeds included: height, density, dry weight, leaf area and for cumin included: seed yield and biological yield.

According to the results of analysis of variance, herbicide treatments had a significant effect on density, height, dry weight and leaf area at different stages of weed sampling. Comparison of mean data on total weed density showed that after weeding treatment, application of pendimethalin preemergence caused an almost 100% reduction in total weed density, which was not statistically significantly different from pre-plant incorporated trifluralin. Concerning weed height, the results showed a significant decrease in the effect of herbicides on weed height. Comparison of means showed that preemergence and pre-plant pendimethalin had a great impact on weed leaf area reduction. Experimental treatments had a significant effect on weed dry weight. Results showed that pendimethalin herbicide had the greatest percentage of reduction in total weed dry weight after weeding treatment. The results of visual assessment also indicated the greater impact of cell division inhibitor herbicides on weed control at all three sampling stages. Preemergence pendimethalin had the greatest efficiency in weed control, whereas metribuzin and prometryn had the least efficiency in this regard. Moreover, the results of visual assessment of herbicide effects on cumin showed that pendimaline had no significant effects on cumin either in pre-plant or pre-emergence applications, probably due to the rapid metabolism of this herbicide in the plant and its low mobility in the soil. The greatest damage to cumin was related to metribuzin. The results showed that the greatest seed yield was related to full-season weeding treatment, followed by pendimethalin herbicide application which caused a 204% increase in the crop seed yield and the lowest seed yield was related to metribuzin with 63% reduction in crop seed yield. It seems that due to relatively long survival of metribuzin in the soil (30-60 days) and the high susceptibility of cumin to this herbicide, it caused severe damage to the crop.

All herbicides applied in this study showed an acceptable level of control over weeds in terms of percentage of density reduction, dry weight, height, and leaf area of ​​weeds. Pendimethalin herbicide after weeding all season had the highest percentage of grain yield and biological yield enhancement, while the least performance was related to metribuzin. According to the results of the visual assessment, the greatest and least impacts of herbicides on weeds was occurred with pendimethalin and metribuzin, respectively. In general, according to the results of this study, pendimethalin herbicide can be effective in controlling weeds and enhancing the yield of cumin because of its greater inhibitory effect on weeds as well as its safety for cumin.