This results in the cost of cleaning the ditch out so that you can get back to the original flow. In addition to the semiaquatic weeds, weeds that are only on land are a problem. These land seeds are usually transported into the irrigation water by leaching or runoff of water. The water-carried seeds are an especially serious problem in irrigated crops. The most sustainable agricultural practice is the use of weed screens, but one should still be concerned with the escapees before they produce seed.
Nurse crops continue to be the preferred method of weed control and seedling alfalfa.
However, nurse crops slow the development of alfalfa and in many situation can be replaced by the use of herbicides thus permitting more rapid establishment. Plots were 10 by 40 ft. Visual crop damage and weed control evaluations were made on April 16 and May 6 and plots were harvested on June 24 1996. Alfalfa injury was greater with glyphosate than paraquat regardless of formulation and tended to increase as rate increased. Alfalfa rapidly recovered from early season injury and by harvest, injury was not evident in any treatment.