Gravity-flow irrigation and the spread of aquatic weeds in Sudan.
The lower stages of the hierarchical distributive and supply canal system used for irrigation in the Sudan are conducive to the spread of aquatic weeds. Among the most prevalent species are Panicum repens, Cyperus rotundus and Ipomoea repens [I. reptans] on canal banks, and Potamogeton spp., Chara globularis, Najas pectinata and Ottelia alismoides anchored in the canal mud. Mechanical clearance using rakes and chains is becoming increasingly uneconomic, but the possible contamination of irrigation water discourages chemical control. See also WA 25, 1635.