防治草害是植物保护的一项重大任务。据国外试验报导:玉米、高粱在播种后3～6周内,受草害可分别减产20％或38％,Knake报导玉米行内,1公尺有“反枝苋”1株或“狗尾草”3株可减产7—10％。Oliver报导大豆行长1公尺内,有3株野牵牛花,可减产52％;有苍耳3株减产61％。孟山都公司报导: Plant protection is a major task of plant protection. According to foreign reports, maize and sorghum can be cut by 20% or 38% respectively within 3 to 6 weeks after sowing. Knake reported that there is 1 copy of “Amaranthus retroflexus” or “Setaria viridis” 1 meter in maize Strains can cut 7-10%. Oliver reports that within three meters of the governor of soybean, there are three wild morning glories, which can reduce the yield by 52%; the three cocks with three cocks reduce the yield by 61%. Monsanto Company reports: