Irrigation and weed infestation.
Problems with weed infestation of irrigation canals were encountered in parts of Uzbekistan, USSR, in areas recently brought under cultivation. Irrigation systems in these areas consist of a series of pipelines feeding raised troughs in which the water distributes less weed seeds and fruits than that in the more conventional irrigation design, a network of channels at ground level. This was attributed to the fact that the troughs are located above the level of the surrounding vegetation, making it very difficult for weed propagules to drop into the water. Instead, weed infestation occurred below the troughs, including such species as Phragmites spp., Echinochloa crus-galli, Chenopodium album, Amaranthus retroflexus and Sorghum halepense. Wind-dispersed seed appeared to be responsible. Appropriate control methods are suggested.