1. Persian Darnel: Identification, Biology and Ecology
Persian darnel (Lolium persicum Boiss. & Hoh.) is an introduced annual or winter annual grass that reproduces by seed. Throughout Montana, North Dakota and the Canadian Prairies it is possible to find Persian darnel plants infesting several crops, including small grains.
Traditionally, Persian darnel has been a weed of limited importance. However, during the last decade Persian darnel has become an increasingly troublesome weed in Montana cropland where it can completely smother patches of wheat or barley and go unnoticed until harvest. This tendency is particularly true in reduced tillage or direct seeding systems that leave weed seeds close to the soil surface.
Persian darnel management presents three main challenges:
Unlike wild oat or kochia (Kochia scoparia L.), which grow above the crop canopy, Persian darnel is short in stature and difficult to see in maturing grain fields. Because of its short height, producers are usually unaware they have a Persian darnel infestation until harvest.
Persian darnel is often misidentified at the seedling stage. Because Achieve (tralkoxydim), Discover (clodinafop) and Hoelon (diclofop methyl) are the only selective post-emergence herbicides that effectively manage Persian darnel in small grains, incorrect identification often leads to improper herbicide selection and unsatisfactory results.
Persian darnel biotypes have developed resistance to several acetyl-CoA carboxylase (ACCase) herbicides including Achieve, Discover and Hoelon. The first case of Persian darnel resistant to ACCase herbicides was reported in 1993, infesting wheat fields.
Successful long-term management of Persian darnel requires a comprehensive plan that integrates several control practices to reduce its abundance and competitive ability.
2. Kentucky Bluegrass Production
The production of Kentucky bluegrass in northern Idaho began during the 1950’s with approximately 10,000 acres and has since grown to 70,000 acres. Idaho produces 50 percent, and the tri-state region (Idaho, Washington, and Oregon) produces 90 percent of the total U.S. Kentucky bluegrass seed (Canode, 1978; Census of Agriculture, 1997). Bluegrass is used in turf grass applications, erosion control practices, and pastures. Acreage in the region has increased due to greater demand, an environment ideally suited for bluegrass production, and the ability of established stands to reduce soil erosion and nutrient runoff, which helps protect the area’s soil and water quality.
Producers have historically burned bluegrass post-harvest residue to maintain stand productivity and profitability. Burning reduces thatch accumulation, viable weed seed, and disease, insect, and rodent incidence. In addition, burning returns nitrogen (N), potassium (K), phosphorus (P), and other nutrients to the soil. Unfortunately, burning has also been associated with significant air quality and public health impacts. Due to these concerns the state of Washington issued a moratorium on burning bluegrass residue in 1996, and restrictions on field burning were implemented in Idaho.
3. Kentucky Bluegrass: Growth, Development, and Seed Production
Burning plant residue is a historical practice that originated with Native Americans to increase plant productivity (Hardison 1976). Modern agricultural burning began in 1944 when the United States Forest Service discovered burning increased the seed production of native pasture grasses in Georgia (Hardison 1976). Burning grass seed fields in the Pacific Northwest began around 1950 to control diseases in perennial ryegrass and tall fescue. Burning has been used in the production of Kentucky bluegrass to maintain seed production and stand longevity. To compare effects of burning and non-burning on bluegrass production see BUL 842, Holman and Thill, 2005.
Unfortunately, emissions created by field burning are associated with negative air quality and public health impacts. Due to these impacts, a moratorium on grass field burning was implemented in Washington State, and restrictions on field burning were implemented in Idaho. Reduced burn and no-burn production systems are currently being researched. The beneficial effects of burning on bluegrass growth and development need to be maintained in reduced-burn and no-burn production systems if high seed production and stand longevity are to be maintained. This bulletin summarizes what is documented about bluegrass growth and development and the effects of burning on seed production.
4. An Industry Amidst Conflict and Change: Practices and Perceptions of Idaho’s Bluegrass Seed Producers
Despite being one of the more economically viable and environmentally adapted crops in northern Idaho, bluegrass seed production has come under increasing scrutiny due to the practice of burning bluegrass post-harvest residue1. Burning is critical to maintain stand longevity and productivity, and protects the environment by reducing soil erosion. Not-burning reduces stand life from an average of about ten years to three, and increases the potential for soil erosion and nutrient runoff. Some residents of northern Idaho counter that the smoke from field burning is a serious public health problem and it curtails tourism during the burn season. In this bulletin, we report the findings of a survey designed to examine the willingness and ability of bluegrass farmers in northern Idaho to adopt potential non-thermal production technologies currently being researched. In addition to the impacts on Kentucky bluegrass seed production, we also report here on the associated social and economic impacts a burning ban would have on the farmers’ ability to continue bluegrass seed production.
Roughly 25 percent of the survey respondents depend upon bluegrass seed production for over 50 percent of their net income. Bluegrass production accounts for seed accounts for 20 percent or less of the net income for 28 percent of producers. Most respondents expressed the sentiment that burning bluegrass residue was one of the most stressful production practices they undertake, but felt it was a practice essential to the economic viability of bluegrass seed production in northern Idaho.
If a ban on bluegrass residue burning were implemented, 92 percent of respondents stated they would decrease the amount of acreage planted to bluegrass. Thirty-six percent stated they would curtail production by over 90 percent. Several factors are identified in the survey that may contribute to the respondents’ apathy towards growing bluegrass seed under a no-burn production system, including:
• A reduction in the economic life of the bluegrass stand from a current ten years to three years.
• An estimated reduction in yield from a current average of 591 (dryland) and 765 lbs/ac (irrigated) to 263 (dryland) and 273 lbs/ac (irrigated).
• An expected increase in labor costs and investment in new equipment, andincreased expense of residue management (i.e. fuel, equipment repair, depreciation, etc.) to adopt a no-burn production system.
• The sentiment by 84 percent of the respondents that an increase in windblown dust and soil erosion, and nutrient runoff would likely occur with a shorter crop rotation and more frequent stand establishment in a non-burn bluegrass production system.
In all, 74 percent of respondents estimated that their per acre net income from bluegrass seed production would decrease by at least 50 percent if they implemented a non-burn production system. Most producers felt strongly about their right to burn bluegrass residue, with just over half stating they would not be willing to sell their rights to burn. If forced to discontinue burning their bluegrass residue, most producers would grow other crops (most likely wheat) on their bluegrass acreage using at least some conventional tillage methods. However, some ground is poorly suited to raising annual crops, and would require either placing the land into CRP or trying to find another perennial crop to produce. Few respondents anticipate selling their agricultural acreage, but almost 40 percent would at least consider selling some land for residential development to ease the adjustment out of a burn production system. Seventy percent of respondents indicated they had a good working knowledge of no-burn production techniques and most indicated they did not think a competitive noburn production method would be developed within the next five to ten years. However, assuming economically viable non-burn methods were developed, 70 percent of respondents indicated confidence they could make the required farming adjustments to continue growing bluegrass seed.
5. Spring Wheat, Canola, and Sunflower Response to Persian Darnel (Lolium persicum) Interference
Integrated weed management practices, such as crop rotation and increased seeding rates, potentially improve weed management. Yet, few studies compare competitive interactions of weeds with different crops. This research quantified the impact of Persian darnel on spring wheat, canola, and sunflower yield across different seeding rates. Increasing crop density increased yield when Persian darnel affected crop yield early in physiological development. Crop yield loss was estimated to reach 83, 70, and 57% for spring wheat, canola, and sunflower, respectively, at high Persian darnel densities. Persian darnel reduced spring wheat yield by limiting the number of tillers per plant and seed per tiller; reduced canola yield by limiting the number of branches per plant, pods per branch, and seed per pod; and reduced sunflower yield by limiting the number of seed per plant. Persian darnel affected crop growth early in physiological development, indicating that interspecific interference occurred early in the growing season. Cultural and resource management aimed at reducing Persian darnel impact on resource availability and crop yield components will reduce Persian darnel impact on crop yield.
6. Persian Darnel (Lolium persicum) Fecundity Response to Spring Wheat, Canola, and Sunflower Interference
Persian darnel control options are limited and unmanaged populations can cause substantial crop yield loss. Integrating crop diversification and higher crop seeding rates into a cropping system might improve Persian darnel management. Field experiments were conducted to determine the effect of different crops and increased crop seeding rates on Persian darnel fecundity. Persian darnel produced up to 2,800 seeds per plant and 3,000 seeds/m2 when grown without competition. Increasing crop density reduced Persian darnel tillers per plant, seed weight, and fecundity. Increasing crop density reduced Persian darnel fecundity 0.4 to 0.2% per spring wheat plant, 0.6 to 0.1% per canola plant, and 16 to 8% per sunflower plant. Persian darnel fecundity was impacted the greatest by reduced weed seedling establishment, which was caused by crop competition and seeding sunflower late in the spring preceded by a nonselective herbicide application. Results indicated delaying the seeding of spring crops or including a late-seeded warm season crop, like sunflower or safflower, in the cropping system is an effective weed management tool for reducing Persian darnel fecundity.