The objective was to develop natural herbicides for downy brome. 5% extracts were obtained from 47 plant species, meadowfoam seed meal (MSM), and pine oil and screened for allelopathy. 10 ml of extracts were then added to petri dishes containing 45 g of sand and 10 downy brome seeds each or wheat seed. The seeds were placed on a filter paper that was placed on top of the sand. Three filter papers were wetted with the extract and placed over the seeds. The Petri dishes were then closed and placed in a germination incubator set at 25ºC for 72 hrs. MSM, Yard-long bean leaves, Blue spruce and Austrian pine needles, Austrian pine bark, and pine oil completely inhibited the germination of downy brome. Leaf extracts of radishes, grain amaranth, mustard, marigolds, brown flax, sugar pea, and pegion pea, inhibited the germination of downy brome roots and shoots by 92 to 99% compared to the control. Root extracts of Lab Lab Rongai, radishes, sugar pea, Tepary bean, grain sorghum, grain amaranth, and hairy vetch inhibited the germination of roots and shoots of downy brome by 82 to 99%. In contrast, root extracts of annual rye grass, marigold petite mix, safflower, robust barley, and white Dutch clover enhanced the germination of downy brome roots by 0.01, 2.8, 4.5, 6.6, and 21.8% above the control. Leaf extracts of barley, white Dutch clover, Tepary bean Tohono, marigold cracker jack mix, marigold sparky mix enhanced the growth of downy brome shoot by 0.4, 0.9, 41, 52, 60, 90%, respectively, above the control. Of the selected extracts evaluated on wheat seed, meadowfoam inhibited wheat germination by 96%. The effect of radishes was variable and inhibited wheat germination by 45 to 81%.