Water plants in the Gezira canals: A study of aquatic plants and their control in the canals of the Gezira cotton area (Anglo‐Egyptian Sudan)

Abstract

The geographical position and climatic conditions of the Gezira cotton area are briefly described. A description is given of the Blue Nile river, and Sennar Reservoir. The common water plants of die latter are listed. It is shown in the case of five of these plants that they tend to be divided in those that occur in shallow water and those that prefer deeper water. Details of the annual rise and fall of the water of the Reservoir are also given.The system of canalization in the Gezira is described and details given of the method of irrigation. A list is given of the common water plants in the Gezira canals, and their distribution over the canalized area is discussed. A comparison is made of the water flora of the canals of Egypt with those of the Gezira.A system of small experimental canals was used to study the life history of the more important water plants in the Gezira canals. Details are given of the extent of the spread of the plants in these canals during a period of 14 months. It was found that abundant growth and seed formation occurred when clear water was entering the canals, but that the bulk of the vegetative part of the plants tended to die when turbid flood water arrived. Abundant seed germination occurred during the turbid water period. Drying the canal bed for 3 1/2 months had little effect on the final quantity of weed developed in the canals when they were refilled. Seed remained viable after 3 1/2 months' dry exposure. Removal of the surface soil from the dry canal bed produced no significant control of the water plants when water again entered the canals. A short flush of water was allowed to flow down the dry canal bed. It was hoped that the seed would germinate and the seedlings be killed by exposure after the flush had ceased. The effect of this treatment on the subsequent plant growth was negligible.Laboratory experiments on the more important water plants showed that the vegetative part of the plants was killed after 8 days' dry exposure to the sun and that mercuric chloride, mercuric chloride‐iodide, and sodium arsenite in a concentration of 1/10,000 killed all plants after immersion in the poison solution for 5 days. At a concentration of 1/100,000 and immersion for 7 days none of these poisons was able to kill Potamogeton nodosus Poir. Work on poisons was discontinued for reasons stated in the text.A short account is given of plants that invade the canals from the banks.The problem of water plant control is discussed, and it is shown that the most hopeful method of control would be a system whereby all infested canals are cleared at regular intervals designed to prevent seeding during the clear‐water period and to remove seedlings during the flood‐water period. The application of this method in the Hag Abdulla Subdivision is described. The successful control that resulted reduced the weeding costs by half.