Comparison of some Vegetative and Reproductive Traits of Dominant Weeds in Cultivated Tomato as Influence by Metribuzin and Non-living Mulches

Introduction: Tomato production, similar to other important crops, is affected by weed competition in the early season. Weed infestation can affect tomato yield significantly. So weed control can be one of the most important factors in improving of crop production. Nowadays pre-plant, post-plant and post-emergence herbicides are widely used for controlling weeds in tomato fields, but it can lead to increasing environmental hazards, making weed resistant to herbicides and injuring tomato plants. Therefore, the use of non-living mulch (organic mulch and inorganic mulch) could be a suitable substitutional way to weed control. Material and method: In this study, in order to investigating the time of emergence, flowering, seed shattering, length of vegetative and reproductive growth period of weeds under six types of non-living mulches (black plastic mulch, clear plastic mulch, wheat straw, sawdust, coco peat and peat moss) and mtribuzin in tomato, research was conducted in a randomized complete block design with three replications at College of Agriculture, Shiraz University in 2012. The plots were fertilized with 20:20:20 (N, P2O5 and K2O) with concentration of 166 kg ha-1. In this study, the appearance of plumule (for narrow leaf weeds) and hypocotyl (for broad leaf weeds) from weed seeds in soil medium was considered as the time of emergence. The weeds were visited once a week since transplanting tomato seedlings to the farm and the related date was recorded. Flowering time recording for each weed species was carried out after flowering. Plots without mulch (weedy and weed free) were used as control. Statistical analysis of the collected data was performed by using SAS 9.1 software and comparing of the mean of characteristics was done by Tukey's test at 5 % significant level. Result and discussion: The longest and shortest time of weed emergence respectively belonged to the clear plastic mulch (28 days after transplanting) and organic mulches and metribuzin (21 days after transplanting). Meanwhile clear plastic mulch effect was significantly different from other treatments, but there was no significant difference among the organic mulches and metribuzin. Also, black plastic mulch and wheat straw respectively showed the highest (66.80 days after transplanting) and the lowest (52.69 days after transplanting) time of weed flowering and both treatments stimulated weed flowering compared to metribuzin (95.33 after transplanting). Weed seed shattering was another important characteristic that was affected by mulch treatment, so that wheat straw showed weed seed shattering at 87.33 days after transplanting while black plastic delayed weed seed shattering until 101.73 days after transplanting. Mulch treatment and metribuzin showed significant differences in their effects on weed seed shattering and metribuzin with seed shattering at 131.29 days after transplanting had the highest effect on it. Also according to the results of current study, there were statistically differences among applied treatments on the length of weed vegetative growth period and mulch treatments showed more efficiency in related to reducing the length of weed vegetative growth period than metribuzin. However wheat straw and clear plastic mulch respectively showed the longest (84.13 day) and the shortest (74.66 day) length of weed vegetative growth period among mulch treatments, but they respectively decreased the length of weed vegetative growth period by 9.20 % and 19.40 % compared to metribuzin. The Length of weed reproductive growth period under mulches, metribuzin and weedy treatments showed that there was no significant difference among all types of treatments. Finally, evaluating tomato yield showed that plots treated with black plastic mulch (20.93 kg/m2), clear plastic mulch (8.31 kg/m2) and metribuzin (6.06 kg/m2) significantly influenced tomato yield. Meanwhile black plastic mulch significantly improved the yield. This is probably due to more effects of black plastic mulch on reducing of evaporation from the soil surface and minimizing of soil temperature and moisture fluctuations that cause better plant growth and yield. Conclusion: According to the results, clear and black plastic mulches had more positive impacts on weed control and yield of tomato than the other treatment. Therefore, it seems that application of non-living mulch can lead to producing high production with higher quality in tomato