UTILIZATION OF ALLELOPATHY FOR WEED MANAGEMENT IN AGROECOSYSTEMS

Biorational alternatives are gaining increased attention for weed cont rol because of concerns related to pesticide usage and dwindling numbe rs of labeled products, particularly for minor-use crops. Allelopathy offers potential for biorational weed control through the production a nd release of allelochemics from leaves, flowers, seeds, stems, and ro ots of living or decomposing plant materials. Under appropriate condit ions, allelochemics may be released in quantities suppressive to devel oping weed seedlings. Allelochemics often exhibit selectivity, similar to synthetic herbicides. Two main approaches have been investigated f or allelopathic weed suppression. One is use of living rotational crop s or mulches that interfere with the growth of surrounding weeds [e.g. , tall red fescue, Festuca arundinacea Schreb.; creeping red fescue, F . rubra L. subsp. commutata; asparagus, Asparagus officinalis L. var. altilis); sorghum, Sorghum bicolor (L.) Moench; alfalfa, Medicago sati va L.; black mustard, Brassica nigra (L.) Koch; and oat, Avena sativa L.]. Attempts to select germplasm with enhanced suppressive ability ha ve been limited. The second is use of cover crop residues or living mu lches to suppress weed growth for variable lengths of time (e.g., wint er rye, Secale cereale L.; winter wheat, Triticum aestivum L.; and sor ghum). Cover crop residues may selectively provide weed suppression th rough their physical presence on the soil surface and by release of al lelochemics or microbially altered allelochemics. The ability to under stand the physiological basis for allelopathy in a crop plant may allo w the weed scientist or ecologist to work closely with molecular biolo gists or traditional plant breeders to selectively enhance the traits responsible for weed suppression.