Effect of Organic Mulch with Pre-emergence Herbicide Combinations on Weeds Control and Saffron Yield

Saffron is a vulnerable crop to weed competition because of its short canopy and narrow leaves. So weeds are the major problem in saffron production. Weeds are mainly controlled by hand or mechanically in saffron fields, these traditional methods are effective and environmental friendly but they are expensive and time consuming.These traditional methods are effective and environmental friendly, however they are expensive and time consuming. The number of suitable herbicide for weed control in saffron fields are limited. The importance of herbicide as alternatives method for weed control was recognized long ago. Herbicide treated mulch (HTM) is the combination of physical (mulch) and chemical (herbicide) weed control methods. This experiment was conducted to investigate the possibility of using mulch and herbicide treated mulch (HTM) to increase the efficiency of herbicides in saffron weeds management. The objectives of this study were to compare the effect of herbicides alone and in combination with mulch on weed control and also determine the influence of herbicide placement (on soil surface, under mulch or herbicide-treated mulch) on weed control and phytotoxicity of saffron.

 Field experiments were conducted during the growing seasons of 2016 and 2017 in Khorasan Razavi, Iran. Two field of 4-year-old saffron that had not received herbicide applications for at least two years in two different climates were chosen. The treatments consist of trifluralin (EC48%) at 1200 g i.a.ha-1, pendimethalin (EC33%) at 1485 g i.a.ha-1 and metribuzin (WP70%) at 525 g i.a.ha-1 were applied in three method 1) Directly to soil: herbicides were applied before crust crushing directly in soil. 2) Under the mulch: herbicides were sprayed with an electric knapsack sprayer after crust crushing directly in soil, then the soil surface was covered with a layer of wood chips mulch with a depth of 3 cm. 3) Herbicide treated mulch: mulch of wood chips were pretreated with herbicides by placing the mulch on a plastic sheet at the depth of 3 cm above and herbicide was sprayed on top of the mulch and evenly mixed and allowed to dry for 48 hours before applying them to field. The non-treated control with and without mulch and also treatment of hand weeding was included for comparison.

 There was no severe phytotoxicity to saffron after treatments application according to EWRC, slight injuries observed in all plots ranging from 1 (No damage) to 2 (Very little damage including slightly yellowing). Metribuzin herbicide induced more phytotoxicity symptoms on saffron compared to two other herbicides, but it was better to weeds control and increasing saffron yield. Treatment of metribuzin mixed with mulch in both fields after hand weeding were the best treatment to decreasing of weeds dry weight and improvement of yield components of saffron. Treatment of metribuzin mixed with mulch compared with control caused 85% and 87% reduction of weed dry weight in both fields, also this treatment compared with control increased dry weight stigma to 2.5 times and 2 times. It seems that after metribuzin, pendimethalin herbicide has better efficiency for use in saffron fields. Although, treatment of mulch without herbicide, is not prevented weed growth, but had more effective on increasing of saffron yield compared to weedy check, especially in field 1(region of Kashmar). Therefore, the use of mulch in warm and dry areas has better effect on saffron yield improvement. Considering that the cultivation of saffron is carried in semi-arid regions of Iran such as Khorasan, the correct application of plant residues in semi-arid regions can have a direct effect on the amount of organic matter in the soil, which leads to an increase in flower yield. Generally the pre-mixed mulch with herbicide, in addition to improving the herbicide efficiency, increased saffron yield. This results indicate that the proper combination of herbicides with mulch layer as thin as 3 cm can provide acceptable weed control. According to the result, one suggested way to weed management in saffron could be the combination of herbicide (Metribuzin) with mulch.