بررسی تاثیر دز و زمان مصرف علف کش پاراکوات بر مهار علف هرز خربزه وحشی (Cucumis melo var.agrestis) در زراعت سویا (Glycine max L.)

To investigate the effect of dose and applying time of Paraquat on soybean weed control, especially wild melon, factorial experiment conducted as a randomized complete block design with four replications in 2009 in Dashte Naz Co. Sari-Iran. The treatments included different doses of Paraquat (0, 1, 1.5, 2 and 2.5 liters per hectare of commercial material) and different growing stages of wild melon (1, 2, 3 and 4 true leaves). The results showed that weeds as velvetleaf (Abutilon theophrasti) and black nightshade (Solanum nigrum) at uni-leaf stage have maximum density compared to other stages. In general weeds at uni-leaf stage of wild melon have more density than the other stages. On the other hand results in the control (dose of 0) treatment showed that weeds competition with crop reduced traits such as plant height and grain weight. Paraquat with 2.5 liters per hectare produced the most number of pods on main stem and lateral branches and produced the most pods per area unit that tends to produce more seeds in the main stems and lateral branches and finally more soybean yield resulted in area unit. Soybean at two and four-leaf stages of wild melon had maximum plant height and lowest pod height respectively. Paraquat, 3 days after spraying at two and three leaf stages of wild melon showed more damage. Also 15 days after spraying, this herbicide eradicates the wild melon at trifoliate stage completely. According to the experiment, application of Paraquat at dose 1 liter per hectare at two and three leaf stages of wild melon leads to satisfactory weed control and high soybean yield as well.