Allelopathic potential of various plant species on downy brome: implications for weed control in wheat production

Allelopathy, the ability of plants to inhibit germination of other plants, is an untapped resource for weed control in crops that could revolutionize organic crop production. The main objective of the study was to evaluate allelopathic potential of various plant species on downy brome (Bromus tectorum L.), a major pest of wheat (Triticum aestivum L.). To screen for potential allelopathy, plants were grown to flowering stage in a greenhouse, separated into shoots and roots, dried, and ground. Five percent aqueous extracts (w/v) were prepared by extracting 5 g of dried, ground plant samples with 100 mL of deionized water. Downy brome seeds were germinated on extract-amended sand. Extracts from most plant species tested inhibited downy brome and wheat seed germination. Extracts from broadleaf plants were more inhibitory than extracts from cereal plants. In most plant species, shoot extracts were more inhibitory to growth of the root and shoot of downy brome than root extracts. Meadowfoam seed meal (Limnanthes alba Hartw.), yard-long bean [Vigna sesquipedalis (L.) Fruw.], blue spruce (Picea pungens pungens Engelm), and pine (Pinus spp.) extracts, which completely inhibited the germination of downy brome seed, have the potential for use in the control of downy brome in wheat-based cropping systems. Meadowfoam seed meal extract inhibited wheat germination by 77 % and root and shoot growth by 97 and 96%, respectively. Radishes reduced wheat germination by 75 to 100%, root growth by 54 to 80 % and shoot growth by 45 to 81%. Plants evaluated in this study have the potential to be used for bio-logically based weed control methods in organic cropping systems. ALLELOPATHY, the ability of plants to inhibit germi-nation of other plants, is so far, an untapped resource for weed control in crops. Yet, it shows con-siderable promise in both conventional and organic agriculture. The U.S. Pacific Northwest (PNW) agricul-ture has traditionally focused on conventional farming systems using synthesized pesticides. In conventional agriculture, weeds can and do develop resistance to pesticides being used to control them, making pesticides less and less effective (Putwain, 1982; Alizadeh et al.