Effect of seed burial and vernalization on germination and growth of Bromus carinatus and its control with several herbicides

Graduation date: 1990California brome (Bromus carinatus Hook & Arn), is\ud considered an important weed infesting wheat and grass seed\ud fields in the Willamette Valley of Oregon. Field and\ud greenhouse experiments were conducted to study some\ud biological aspects to develop more efficient management\ud strategies.\ud A field experiment was conducted to determine the\ud effect of depth (0 to 30 cm) and duration (1 to 11 months)\ud of burial on germination, viability, and soil longevity of\ud seed. Seed depletion was directly related to depth and\ud duration of seed burial. Surface-sown seed germinated\ud gradually, reaching 81% after 7 months. Buried seed\ud germinated rapidly. Less than 3% of the initial population\ud remained ungerminated after 1 month at all depths. Seed\ud loss at depths of 10 to 30 cm was primarily due to in situ\ud germination, with little effect from induced or enforced\ud dormancy. Persistence of surface-sown seed was due to both\ud enforced and induced dormancy, with enforced dormancy being\ud the more important mechanism of seed persistence. Highest\ud degree of enforced dormancy (34%) was at 1 month, decreasing\ud after 3 months. Properly timed tillage can be important for\ud effective control since tillage increases germination,\ud reducing soil persistence.\ud Greenhouse experiments were conducted to determine if\ud imbibed seed vernalization promoted plant flowering. In the\ud first experiment, cold treatment (5 C) of 10, 15, and 20\ud days reduced the vegetative phase. Flowering was absent in\ud plants from seed receiving 5 days of cold and in\ud unvernalized plants after 96 days, when this experiment was\ud terminated. Plants from seeds vernalized for 20 days\ud flowered within 36 days after transfer from cold treatment\ud to the greenhouse. Number of culms per plant and shoot dry\ud weight were highest on unvernalized plants and plants\ud vernalized as imbibed seed for 5 days. Lengthening the\ud vernalization period from 10 to 20 days decreased the total\ud seed dry weight from 18.78 to 15.02 g. The ratio of total\ud seed dry weight to total shoot dry matter was highest for\ud plants vernalized as imbibed seed for 20 days. In the\ud second experiment, only plants from seed vernalized for 20\ud days flowered within 109 days after transfer to the\ud greenhouse, whereas plants from seed vernalized for 0, 5,\ud 10, and 15 days did not flower. There was not a statistical\ud difference for number of culms per plant. Plant height was\ud consistent in all treatments, with the exception of plants\ud vernalized for 20 days, which were taller than plants of the\ud other treatments. Highest total shoot dry weight was\ud observed on plants from seed vernalized for 15 or 20 days.\ud The effect of differential soil placement of\ud cinmethylin (exo-l-methyl -4-(methylethyl)-2-[(2-\ud methylphenyl)methoxy]-7oxabicyclo[2.2.1] heptane), diclofop\ud ((±)-2-[4-(2,4-dichlorophenoxy)phenoxy]-propanoic acid),\ud triallate (S-(2,3,3-trichloro-2-propenyl) bis(1-\ud methylethyl)carbamothioate), and trifluralin (2,6-dinitro-\ud N,N-diprony1-4(trifluoromethyl) benzenamine) on California\ud brome control was measured in the greenhouse, at a rate of\ud 0.93, 1.8, 1.34, and 1.07 ppm, respectively. Cinmethylin\ud had the greatest affect on plant height and plant weight,\ud reducing both significantly. California brome plant height\ud and dry weight were not affected by herbicide placement.\ud Seedlings treated with diclofop with shoot plus root\ud exposure differed in plant height from those treated only in\ud the shoot or root zone. Seedlings with shoot exposure to\ud triallate did not differ in height or dry weight from plants\ud treated in the root or shoot plus root zone. Root exposure\ud to trifluralin reduced height and dry weight less than did\ud shoot or shoot plus root exposure