ABSTRACT
This chapter stresses the beneficial as well as the harmful economic and ecological aspects, and emphasizing that a better understanding of the biology of weeds is key to managing both their adverse and advantageous potentials. It discusses the agricultural weeds barnyard grass, Bermuda grass, and weedy rice. In addition to being an extremely competitive agricultural weed, in some soils, barnyard grass accumulates high levels of nitrates which can poison livestock, and it is also a host for several insect pests and virus diseases of crops. Barnyard grass is considered to be a millet, but the following millet species are more important. Extremely extensive research has been conducted on the harmful aspects of the nutsedges and their control. Indeed, in North America where yellow nutsedge is probably indigenous, it is considered to be a valuable food source for wildlife, meriting maintenance. Because weedy rice is the most serious weed of rice, it is sometimes called the world's worst weed.
