Yield, Essential Oil and Some Morphological Characteristics of Peppermint (Mentha piperita L.) influenced by Hand Weeding and Plant Density

The effects of hand weeding and plant density on yield, rate of essential oil and some morphological characters of peppermint (Mentha piperita L.), investigated by factorial experiment based of randomized complete block design with three replication over two cuts in Hamedan in 2012-13. Experimental factors were weed controls in two levels (hand weeding and without weed control (weed infested)) and plant density in three levels (6,10,14 and 18 plants.m-2). Johnsongrass (Sorghum halepense L.), Field bindweed (Convolvulus arvensis L.), Wild oat (Avena fatua L.), Black night shade (Solanum nigrum L.), Common mallow (Malva neglecta Walr), Hoary plantain (Plantago media L.) and Common lamb’s quarters (Chenopodium album L.) are included as identified weeds in the field. The results in both cuts showed that weeds caused a decrease in qualitative and quantitative characters in peppermint. Peppermint plants had grown better in the first cutting than the second cutting. Plant harvested in the first cutting had higher dry and fresh yield and essential oil yield. Hand weeding caused increase in fresh and dry weight, essential oil yield, leaf area and percentage green cover. Increase in density had dramatic effects on increase of dry and fresh weight, yield of essential oil and percentage green cover, highest efficiency in above mentioned, was obtained in 18 plants.m-2 plant density. Results indicated that to increase peppermint’s quality and quantity it’s required to observe optimal density.