VENTENATA BIOLOGY AND DISTRIBUTION IN THE PACIFIC NORTHWEST. Pamela Pavek*1, John Wallace2, Timothy Prather2; 1NRCS Plant Materials Center, Pullman, WA, 2University of Idaho, Moscow, ID (124)
In the last two decades ventenata [Ventenata dubia (Leers) Coss.] has spread rapidly along transportation corridors, in pasture, hay land, range and Conservation Reserve Program (CRP) fields throughout the Pacific Northwest. Data collected in 2008 from a survey sent to Natural Resources Conservation Service (NRCS) field staff and an 800 km traverse through eastern and central Washington, northeastern Oregon and northern Idaho revealed ventenata grows in areas receiving 35 to 112 cm annual precipitation at elevations ranging from 10 to 1800 m. It is most commonly found on south-facing slopes and in shallow, rocky clay or clay-loam soils that are saturated or inundated in early spring. However, it can also be found on other aspects and soil types. In areas with disturbance such as grazing, ventenata appears to be displacing desirable vegetation. In undisturbed areas it may be replacing desirable vegetation as growth is hindered by old age, disease, or lack of nutrients, and may be preventing desirable vegetation from reproducing by occupying open niches. Ventenata is a winter annual grass in the Aveneae tribe that has a shallow root system, one to few tillers and produces 15 to 35 seeds per plant. Ventenata seed has a bent and twisted awn which, similar to wild oat (Avena fatua L.) “unwinds” when it becomes wet and drills the seed into the soil. Seed typically germinates in the fall about 2 weeks after downy brome (Bromus tectorum L.). Similarly, ventenata produces seed heads in the spring 2 to 4 weeks after downy brome. Greenhouse experiments indicate vernalization is necessary for seed head production. Ventenata seed has little or no innate dormancy, however dormancy may be induced if seeds are exposed to cold temperatures. Seed placed in a germinator at 18 C with 10 hours of light began germinating on Day 4 and achieved 85% germination by Day 26. Seed chilled for 5 days at 1 C prior to being placed in germinator began germinating on Day 9 and reached a maximum of 30% germination on Day 68. Seed chilled for 10 days at 1 C began germinating on Day 31 and reached a maximum of 35% germination on Day 64. In soil, seed may be viable for only 1 or 2 years. Seed in packets buried at 2 cm and 8 cm at two sites had an average germination of 82% and 80%, respectively, after 1 month and 0% germination after 6 months. After 1 year there was one germinating seed (at 2 cm depth) indicating there may be a small amount of variability in dormancy. Grazing and mowing ventenata are not effective management options. If the plant is grazed or cut when soil moisture is available it will regrow from within the same tiller and produce viable seed. Depletion of soil moisture is typically a trigger for seed head production, and during this phase the plant has high silica content (~2.7%) which causes it to become unpalatable to livestock and difficult to mow or swath. Fire is also not an effective management option; survey respondents reported in areas where fires have occurred, ventenata is more prevalent. Ventenata is of ecological concern because it may impair the functions and productivity of grassland systems.