The critical period of chickpea weed control in dry-land conditions of Kurdistan province

Chickpea has the highest harvest area and production quantity among pulse crops in Iran. This crop is a poor competitor against weeds. So understanding the critical period of weed control (CPWC) is important for determining proper time of weed management and herbicide application. The objective of the experiment was to determine the CPWC of chickpea in dry-land conditions of Dehgolan plain in Kurdistan province.

The field experiment was carried out as randomized complete block design with four replications at agricultural research station of Kurdistan University in Dehgolan plain, Kurdistan province from April 18, to July 21, 2014. The chickpea cultivar ILC 482 was used for the study. The trial had 16 treatments, including seven non-weeding (Interference) periods and seven weeding (weed-free) periods as well as whole season weed free and weed interference as control. Weed interference and weed-free treatments were set up as 12, 22, 32, 42, 52, 62, and 72 day periods after planting. The beginning and the end of CPWC was determined by curve fitting to weed interference and weed free periods respectively. Relative seed yield of treatments was calculated as percent of weed-free control. A four parameter logistic equation was fitted to relative yields of weed interference and weed-free periods and then CPWC was determined based on 2.5, 5, and 10 percent acceptable yield loss (AYL).

Weed density of interference periods ranged 9.98-17.42 and the mean density was 14.82 plant m-2 during growing season. Mean density of Chenopodium album, Convolvulus arvensis, Carthamus oxyacantha, and Amaranthus retroflexus were 8, 4, 1.5, and 0.5 plant m-2 respectively and composed the major species of weed community. Weeds dry weight increased linearly as interference period increased and reached 62.13 gm-2 on harvest time. In contrast, weeds dry weight decreased exponentially with increasing weed-free periods and approximately approached zero at the end of growing season. Seed yield of weed-free and weed interference controls were 106.38, and 68.71gm-2 respectively. Therefore, weed interference reduced seed yield by 35.5% compared to weed-free control. The beginning of CPWC was estimated 208, 292, and 426 degree days (18, 24 and 36 days after planting) equal to 3, 5, and 8 chickpea leaf stage and the end of CPWC was also determined 1234, 969, and 720 degree days (79, 67 and 54 days after planting) equal to mead seed filling, the end of podding, and early flowering according to 2.5, 5, and 10 percent yield loss.

The CPWC was determined 24-67 days after planting (the 5 leaf stage to the end of chickpea podding) based on 5% yield loss.