Biology and Management of Rattail Fescue in Direct-Seed Systems

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1 Biology and Management of Rattail Fescue in Direct-Seed Systems Dan Ball Oregon State University Pendleton, OR Introduction Rattail fescue (Vulpia myuros) has been a localized problem in certain areas of the PNW for many years, but more recently has emerged as a significant new problem for dryland wheat producers using direct-seeding practices. It is also an increasing problem for turfgrass seed producers throughout the region. Rattail fescue has long been a problem weed of crops and grasslands in many temperate regions of the world. It occurs extensively in southern Australia, and southwestern and central Europe, where it is referred to as silvergrass. It is reportedly more common in direct-seeded crops in these areas. Rattail fescue tends to prefer light to medium textured soils with a slightly acid ph. Plants are shallow rooted and sensitive to drought conditions, which appear to limit its spread in its native Mediterranean region. In the PNW, increased adoption of direct- seeding is contributing to increases in rattail fescue infestations. The shallow rooting plants do not tolerate tillage, and seeds will not germinate if buried deeper than one half inch in the soil. In addition, conventional rates of glyphosate have proven ineffective in controlling rattail fescue in direct-seed systems and in chemical fallow. Because concerns have been increasing among PNW dryland wheat producers about the incidence of rattail fescue in direct- seed cropping systems, a new STEEP III funded study is being undertaken in the PNW states to gain a better understanding of some basic biological characteristics of rattail fescue, and to develop control practices in direct-seed, dryland cropping systems. Little information exists on the biology of this grass weed. In addition, few options for effective control without tillage in fallow and in cereal crops exist, and need to be developed. Information is needed on optimum temperatures for seed germination, the characteristics of seed dormancy, vernalization requirements, and longevity of seed in the soil. This information will provide a better understanding of the life cycle of rattail fescue, and also facilitate the design of management strategies in cropping systems. Rattail Fescue Seed Biology Optimum temperatures for ratatil fescue seed germination. Seed from a collection of rattail fescue obtained near Hermiston, Oregon, was dry stored 3 years and used to determine optimum seed germination temperature. A two-way thermogradient plate was used to investigate germination requirements. Alternating temperatures of 16- hour day/8-hour night, were established. Initial conditions were 40/40 ºC (day/night temperature) on the high end of the plate and 5/5 ºC on the cool end. A total of 64 temperature regimes were monitored. The study was repeated three times. Germinated seed was counted every 3 days, and at the end of 18 days total germination recorded. Many germination temperatures resulted in similar levels of rattail germination. Maximum germination occurred at around 20/20 ºC day/night temperature, or about 68 ºF. Rattail fescue seed dormancy. An on-going study is being conducted to investigate the primary (after-ripening) dormancy in Rattail fescue (Vulpia myuros) seed. Germination was tested on freshly harvested seed, and on seed after dry storage for 1 month. Seed used in this study was obtained from an irrigated fine fescue research plot at Hermiston. The study evaluated germination promoting factors of temperature, and pre-chilling. Temperatures were set at a constant 20 o C in darkness or a constant 30 o C in darkness, and chill treatments were either no chilling prior to germination, or or chilling at 5 o C for 5 days prior to germinating. Rattail fescue germination was greater at 20 o C than at 30 o C, and pre-chilling of seed improved germination of fresh seed (Table 1). These results are consistent with that typically observed in weeds categorized as being true winter annuals. This study will continue for a 1-year period. 93

2 94 Table 1. Effect of dry storage time, germination temperature and pre-chilling on Vulpia myuros seed germination. Germination temperature Pre-chill Freshly harvested 1-month-old seed seed ( o C) % - 20 Chill No chill Chill No chill 0 0 LSD (0.05) Rattail fescue seed longevity in the soil. An on-going study is being conducted to evaluate the influence of burial time and burial depth on germination in rattail fescue at three sites in eastern Oregon. Three burial sites were located near LaGrande and Pendleton, Oregon. All sites were dryland with no irrigation. Nylon mesh packets, containing 100 seeds were buried at different depths. Packets were buried in September, and exhumed after burial for 6 months and 1 year. Collected seeds were air dried, pre-chilled for 5 days at 5 C in the dark, and placed in a continuous 20 C, dark germination chamber. Germination counts were taken after 21 days. Seed buried for a six month period appeared to be dormant when exhumed in March (6-month burial). After burial for 1 year, seed germination varied from 1% to 30% depending on location (Table 2). The LaGrande site was on a high ph soil (9.0 ph). The Summerville and Pendleton sites were on soils with ph typical for the region, and the Summerville sight tended to be a cooler, higher elevation site than Pendleton. The study will continue for an additional 2 years. Table 2. Rattail fescue seed germination response to burial at five depths for two time periods at three locations in Oregon. 6-Month burial 1-Year burial Depth Pendleton Summerville LaGrande Pendleton Summerville LaGrande (in) % germination

3 95 Rattail Fescue Management in Chemical Fallow. Rattail fescue can be controlled with high levels of tillage, but control is poor with application rates of glyphosate typically used during chemical fallow periods in direct-seed systems. This leads to increasing infestation levels of rattail fescue in chemical fallow and subsequent direct-seeded cereal crops. Preliminary research in Oregon showed high rates of glyphosate applied in the spring are insufficient to eliminate seed head production (Table 3). Later application timing of glyphosate when plants have sufficient surface area to may be helpful at improving control with glyphosate (Table 3). In addition, higher glyphosate application rates than those typical of dryland wheat producers, and split applications of glyphosate helped improve control of rattail fescue (Table 4). More research is needed to determine optimum rates and timing(s) for herbicide application during fallow periods under a range of PNW agronomic zones. Table 3. Rattail fescue control in chemical fallow. Mission, OR, Treatment Product Rattal Fescue Rattail Fescue Rattail Fescue Rate control control Seed Production 14 DAT 60 DAT 50 DAT fl oz/a % % # seeds/m 2 Weedy check ,000 Roundup UltraMax 13.0 (16) ,600 Roundup UltraMax + AMS 13.0 (16) ,100 Roundup UltraMax 16.2 (20) ,500 Roundup UltraMax + AMS 16.2 (20) ,000 Roundup UltraMax 19.5 (24) ,700 Roundup UltraMax 25.9 (32) ,000 Roundup UltraMax 32.4 (40) ,200 Engame 48.8 (20) ,400 Engame 78.0 (32) ,900 Gramoxone Extra ,000 Gramoxone Extra + Sencor oz ,700 Gramoxone Extra + Sencor oz ,600 Surefire ,000 LSD (0.05) ,000 All treatments except Roundup UltraMax received R-11 at 0.25% v/v. All treatments applied on April 17, AMS added at 8.5 lb/100 gal. for indicated treatments. Product rate amounts in parentheses indicate equivalent rates of Roundup Original. Sencor rate expressed as oz/a dry weight of 75% DF.

4 96 Table 4. Rattail fescue control in chemical fallow. Walla Walla, WA, Treatment 1 Rate 2 Timing 3 Rattail Rattail Rattail fescue control contro seed production fl oz/a % seeds/m 2 Roundup UtraMax 25.9 EPOST ,200 Roundup UtraMax 32.4 EPOST ,400 Roundup UtraMax 38.9 EPOST ,800 Engame 78.0 EPOST ,600 Engame 97.5 EPOST ,500 Engame EPOST ,800 Roundup UtraMax/ Roundup UtraMax 19.5 / 19.5 EPOST/ LPOST ,200 Roundup UtraMax/ Roundup UtraMax 25.9 / 25.9 EPOST/ LPOST Engame / Engame 58.6 / 58.6 EPOST/ LPOST Imazamox 6 EPOST ,900 Roundup UtraMax 25.9 MPOST 74 17,800 Roundup UtraMax 32.4 MPOST 71 19,400 Roundup UtraMax 38.9 MPOST 86 10,300 Engame 78.0 MPOST Engame 97.5 MPOST 94 1,000 Engame MPOST Imazamox 6 MPOST 44 4,500 Untreated check 130,600 LSD (0.05) ,900 1 Nonionic surfactant (R-11) added at 0.25% v/v to Engame and Imazamox treatments. Urea ammonium nitrate (32%N) at 2.5% v/v was also added to the Imazamox treatments. 2 Rates for Imazamox are expressed as lb ai/a. 3 EPOST applications made April 10, 2003 to 5- to 7-leaf rattail fescue. LPOST applications made May 6, 2003 to rattail fescue in the two-node stage of growth (jointing). Rattail Fescue Management in Direct-Seeded Wheat. Herbicide effectiveness trials conducted in winter wheat under irrigated conditions indicate that potential treatments exist for control of rattail fescue in winter wheat (Table 5). However, no treatments are currently registered for rattail fescue control, and little work has specifically been conducted in dryland wheat cropping systems in the PNW. The effectiveness of potential herbicide treatments for control of rattail fescue in dryland, direct-seeded winter and spring wheat systems is needed to secure appropriate herbicide registrations in the PNW.

5 Table 5. Rattail fescue control in irrigated winter wheat. Hermiston, OR, Rate Timing Wheat Wheat Rattail Rattail Wheat injury injury control control yield 3/7/00 5/3/00 3/7/00 5/3/00 (product/a) % - bu/a Check Maverick 0.67 oz PREPLA Axiom 6 oz PREPLA Axiom 9 oz PREPLA Axiom 11 oz PREPLA Karmex 1.5 lb PREPLA Maverick + R oz EPOST Axiom + R-11 6 oz EPOST Axiom + R-11 9 oz EPOST Axiom + R oz EPOST Olympus + R oz EPOST Olympus + Sencor + R oz + 4 oz EPOST Maverick + R oz LPOST Olympus + R oz LPOST Olympus + Sencor + R oz + 4 oz LPOST LSD (0.05) Wheat var. WB 470 seeded 10/12/99; PREPLA preplant treatments applied 10/12/99; EPOST applied 11/15/ 99 to 2.5 leaf wheat and 3 leaf rattail; LPOST applied 3/4/00 to 7-leaf wheat and tillered rattail. Postemergence treatments received R-11 nonionic surfactant at 0.25 % v/v. Some treatments evaluated on 5/3/00 could not be evaluated due to heavy infestion of annual bluegrass. Note: None of the above treatments are registered for control of rattail fescue in wheat. These treatments are experimental, and are not to be considered as a product endorsement or recommendation for use.