Defatted seedmeals from 15 glucosinolate-containing plant species were analyzed for herbicidal activity by determining inhibition of seedling emergence when added to a sandy loam soil containing wheat and sicklepod seeds at concentrations of 0.1, 0.5, and 1% (w/w). In general, the seedmeals were more phytotoxic to wheat than sicklepod. For wheat, all of the seedmeals significantly inhibited seedling emergence at the 1.0% concentration. At the 0.1% concentration three of the seedmeals (Indian mustard, money plant, and field pennycress) completely inhibited wheat emergence. For sicklepod emergence, eight of the seedmeals were completely inhibitory at the 1% level (Indian mustard, field pennycress, garden rocket, Siberian wallflower, English wallflower, garden cress, sweet alyssum, and evening stock) and four were completely inhibitory at the 0.5% level (brown mustard, garden rocket, English wallflower, and sweet alyssum). Intact glucosinolates and their corresponding hydrolysis products varied among the seedmeals with the highest activity. Major hydrolysis products produced by the seedmeals with the most phytotoxicity, respectively, included 2-propenyl (allyl) isothiocyanate (AITC) by brown mustard seedmeal, allyl thiocyanate and AITC by field pennycress seedmeal, erucin (4-methylthiobutyl isothiocyanate) by arugula seedmeal, 3-butenyl isothiocyanate and lesquerellin (6-methylthiohexyl isothiocyanate) by sweet alyssum seedmeal, and isopropyl isothiocyanate by money plant seedmeal. From our data it appears that both the type and concentration of glucosinolates and their hydrolysis products present in the seedmeals affect seed-emergence inhibition.
Nomenclature: English wallflower, Erysimum cheiri (L.) Crantz; evening stock, Matthiola longipetala (Vent.) DC. MTLLB; Field pennycress, Thlaspi arvense L. THLAR; garden cress, Lepidium sativum L. ‘Cressida’ LEPSA; garden rocket, Eruca vesicaria (L.) Cav. subsp. sativa (Mill.) Thell. ‘Astro’ ERUVE; Indian mustard, Brassica juncea (L.) Czern. ‘Southern Giant Curled,’ BRSJU; money plant, Lunaria annua L.; Siberian wallflower, Erysimum × allionii; sicklepod, Senna obtusifolia (L.) H. S. Irwin & Barneby CASOB; sweet alyssum, Lobularia maritima (L.) Desv. LOUMA; wheat, Triticum aestivum L. ‘Cardinal’.