JWSS - Journal of Water and Soil Science

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In order to find the critical period of weed control, the best time of weed control beginning (i.e. herbicide application time), and the length of weed control period (i.e. herbicide persistency) in corn, field experiments were conducted in Bajgah and Kooshkak in Fars Province in 1995 using a randomized complete block design with 14 treatments and four replications. Treatments consisted of different times of weed control beginnings (20, 30, 40, and 50 days after corn emergence), different duration of weed control periods (10, 20, and 30 days), a weedy check, and a weed-free check during the period of corn growth.

 In Kooshkak, a 10-day duration of weed control period had significantly lower corn yields than 20 and 30-day periods. In Bajgah, a 10-day weed control period had significantly lower corn yields than a 30-day period. Time of weed control beginning was not significant at both locations however, the interaction between beginning time and the duration period of weed control was significant. It appears in both locations that a minimum 20-day control period at the initial stages of corn and weed growth, and a minimum 30-day control period before corn pollination are necessary to prevent corn yield losses. In order to prevent corn leaf area decline at both locations, a 20-day weed control period until 40 days after crop emergence is necessary.

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The recent years' problems of herbicide use have led a growing number of researchers to seek alternative methods that are less reliant on herbicides. This research was conducted to determine the effect of long-term crop rotation, mineral fertilizer and herbicide on the weed infestation and grain yield of winter rye during 2004 and 2005 at the long-term experimental site of the University of Timiriazev, Moscow. Treatments were control (no weed control), herbicide, combined fertilizer (NPK) and NPK plus herbicide in field winter rye cultivated in continuous and crop rotation with other crops since 1912. Crop rotation significantly decreased weed density and dry mass. Long-term NPK application significantly decreased weed density, but had not any effect on weed dry mass. Crop rotation, NPK application and herbicide increased ground crop cover and decreased ground weed cover. In continuous crop, weed ground cover was 10 % in control plot and 3.33 % in plots where NPK was applied. Data showed that long-term crop rotation and NPK application can reduce weed infestation and increase grain yield of winter rye.