Integrated weed management of cumin (Cuminum cyminum L.) using reduced rates of herbicides and straw mulch

Cumin (Cuminum cymium L.) is an annual plant with delicate stems and a height between 15 and 50 cm. For high yield and increased product quality, consuming the appropriate amount of dinitroaniline herbicides and using mulches to control weeds is important. Therefore, the use of trifluralin, pendimethalin herbicides, and wheat mulch was investigated in this experiment to investigate the population and growth of weeds, physiological and vegetative characteristics, yield, and percentage of cumin essential oil.

This experiment was conducted as a randomized complete block design with three replications. In this study, the experimental treatments included 100% and 50% recommended amounts of trifluralin and pendimethalin herbicides alone and in combination with wheat stubble mulch, which was considered together with wheat stubble mulch alone and no weed control (control). Wheat stubble mulch, 5 cm long and equal to 5 tons per hectare, was applied. The herbicide was spread using a 20-liter book-back sprayer with a rain nozzle. Weed species were identified by Zarghan Agricultural Research Station, Fars Province weed experts. After that, quadrats with dimensions of 50 x 50 cm were used to determine weeds' density and dry weight. Three fully opened and fresh young leaves were selected to measure the relative water content of leaves and the chlorophyll content of each treatment. Sampling was done in the morning and before sunrise. Before the end of the growth period, the height and number of branches were measured. After harvesting, yield and yield components (including the number of umbels per plant, the number of seeds per umbel, and the weight of 1000 seeds) were determined. From the harvested seeds in each plot, 50 grams of samples were randomly taken and analyzed to determine the percentage of essential oil. To extract essential oil from the prepared samples, the steam distillation method was used by a Clevenger machine. The percentage of essential oil in each sample was determined. The mean comparison of the studied traits was compared using Duncan's multiple range test at 0.05.

The dominant weed species identified in the field included 6 genera and 6 species. The mean comparison results showed that using trifluralin herbicide with the recommended dose + mulch reduced weeds' density and dry weight by 88% and 87%, respectively, compared to no weed control (control). Mulch treatment alone reduced weed density and dry weight compared to control plants by 29.6% and 37.5%, respectively. 85% mulch + trifluralin herbicide at the recommended dose resulted in the highest relative leaf water content. Also, the highest chlorophyll b and total leaf chlorophyll content were obtained for both trifluralin and pendimethalin herbicides in combination with mulch, which showed a significant increase compared to mulch alone and no weed control. The lowest cumin plant height was observed in the weed-infested treatment (control). Among the management treatments, the number of lateral branches in the treatment of 100% of the recommended herbicide dose was more than in the treatment of 50%. Also, adding mulch to the treatments showed a significant increase in lateral branches. Cumin aerial parts dry weight increased by 4% with the 50% dose and 10% with the full dose. With trifluralin herbicides, cumin seed yield increased by 47% and pendimethalin by 45%. By applying mulch management treatments, cumin seed yield increased by 48%.

The application of wheat mulch, by increasing leaf water and chlorophyll's relative content, improves growth indicators. In addition to the application of 100% of the recommended dose of trifluralin and pendimethalin herbicides in combination with wheat mulch, which increased the dry weight of shoot and seed yield in cumin, the treatment of 50% of the recommended dose in combination with wheat mulch at a lower level improved these traits. Therefore, due to reduced herbicide consumption, 50% of the recommended dose of trifluralin herbicides in combination with wheat mulch is recommended to control weeds in cumin.