ABSTRACT
Allelopathy could contribute toward the aggressiveness of weeds in weed: crop interference or in patterning of weeds in a field through influences of their exudates, leachates, volatiles, or litter products. Proof of competitive interference is as necessary as proof of allelopathy. Chemicals with allelopathic potential are present in virtually all plant tissues, including leaves, stems, roots, rhizomes, flowers, fruits, and seeds. Allelochemics may be released from plant tissues in a variety of ways, including volatilization, root exudation, leaching, and decomposition of the plant residues. Simple aliphatic acids are formed upon anaerobic decomposition of plant residues in soil. Acids are released from decaying quackgrass residues and the straw of cereal grains. Many plant residues contain gallic, ellagic, or digallic acids. Several of the more common hydrolyzable tannins are sugar esters of gallic acid, while others are complex mixtures of several phenolic acids.
