NCERA184: Management of Small Grain Diseases
Statement of Issues and Justification
Small grains, particularly wheat, barley, and oats are significant crops in many states east of the Rocky Mountains (source: USDA-NASS). Of these, wheat is the most economically important and multiple classes are grown in this region, including: hard red winter (southern and central Great Plains), hard red spring and durum (northern Great Plains), soft red winter (central and southeastern U.S.), and soft white winter (northeast and north central U.S.). Also, the acreage of hard white wheat planted in the Great Plains has continued to increase in recent years with the release of improved varieties. Barley, oats, and to a lesser extent rye and triticale are also regionally important in the eastern U.S. and represent significant crops in certain states (e.g. barley in North Dakota, oats in South Dakota and Oklahoma).The combined value (farm gate) in 2005 for the grain from these crops was nearly $5.4 trillion (source: USDA-NASS). The primary uses of the grain are: for human consumption (flour, bran, etc.), as livestock feed, and malting and brewing (barley). These crops may also be used for hay, straw, and silage production or even directly grazed (e.g. dual-purpose, graze-grain wheat). Additionally, the small grains are being investigated for potential use in biofuel production as both grain-starch and cellulosic sources because they can often be grown in areas where corn and soybeans cannot (e.g. winter wheat in the western Great Plains).
The production of small grains has declined substantially over the last 20 years in the United States for several reasons. First, the price paid for grain has changed little during that time and thus the value for several of these crops has actually declined when adjusted for inflation. To add to the financial issues, government subsidies for many of the small grains are less competitive than those for other crops (e.g. corn and soybeans). Second, diseases continue to have a profound affect on both grain yield and quality and shifts in agronomic practices have complicated disease management strategies further (see below), making it difficult to maintain profitability. Third, the massive expansion of genetically modified (GM) crops (i.e. corn and soybeans) has made small grains much less attractive to producers because of the relatively more complicated and expensive weed and pest management strategies sometimes required for small grains. Finally, small grains are currently less efficient than corn for biofuel (ethanol) production. When all of the above factors are considered, small grains are simply less competitive economically than corn and soybean for much of the eastern U.S. and thus their acreage has gradually declined.
Interestingly, several of these same factors may result in a future increase in the acreage planted with small grains. First, the dominance of glyphosate (e.g. Round-Up) resistance in corn and soybean is causing a shift in the sensitivity of some weeds to this herbicide and a loss of sensitivity in others. This will complicate future weed management strategies in these crops. Second, the lack of crop diversity has resulted in very short rotations that allow pest and pathogen populations to remain high and regularly impact yield. Thus, the management of weeds and diseases in crops presently used as alternatives to small grains is becoming more difficult and expensive. Third, these crops are essentially in a monoculture with limited genetic variability making them susceptible to disease epidemics (e.g. Asian soybean rust) or insect pests. Finally, the increasing costs of fertilizer and fuel, and scarcity of irrigation water in some regions is making it difficult for producers to maintain profitability, especially for corn. A recent development that may also impact production of small grains is that the rapid expansion of biofuel generation using corn and soybean is diverting the grain from these crops away from human and livestock consumption. Small grains may be used to fill the niche left from the biofuel-associated changes in crop utilization as well as for biofuel production directly. Overall, the addition of small grains to current rotations would add diversity to the dominant cropping systems and potentially reduce the impact and severity of the pathogens and pests of all crops.
The agronomic practices utilized for growing small grains have changed dramatically in the last two decades as a large percentage of producers are; using reduced tillage practices, planting earlier, and using shorter rotations (limited fallow periods) to reduce soil erosion. Many are also more intensively managing their crops by applying higher amounts of fertilizer to maximize economic returns. All of these factors have had profound effects on the incidence and severity of the diseases of small grains. The residue-borne diseases, such as Fusarium head blight (FHB), tan spot and Septoria diseases of wheat, occur annually in much of the region and have increased following the adoption of reduced tillage practices with a significant impact on both crop yield and quality. Epidemics of FHB in particular have devastated the wheat and barley crops in entire regions (e.g. the northern Great Plains), resulting in millions of bushels in lost production, numerous farm and equipment sales, and disruption of entire rural communities. By gaining a better understanding of the epidemiology of the diseases of small grains in both current and emerging production systems, we can develop economically sound management strategies for producers.
In order for producers of small grains to remain profitable while addressing the future needs of consumers, the impact of diseases on crop yield and quality must be mitigated. Unfortunately, this is difficult not only because of changes in agricultural practices but also because many of the pathogens attacking these crops are dynamic in both their geographic distribution and ability to infect cultivars. For example, stripe rust of wheat was more of a curiosity than a concern in the Great Plains prior to 2001. Since then, it has caused regular losses in several states that reach into the millions of bushels and dollars (e.g. Texas and Kansas in 2005). Thus stripe rust has quickly become one of the most economically important diseases of wheat in the entire United States. Other rust diseases of small grains, specifically leaf rust of wheat and crown rust of oats, continue to cause significant losses, even after many years of breeding efforts to improve the resistance in commercial varieties.
In contrast to the aforementioned rust diseases, stem rust (caused by Puccinia graminis) has received very little attention from plant pathologists and breeders lately because it has been effectively controlled through stable host resistance and the barberry eradication program (which targeted the alternate host). As a result, a minimal effort has been put into the introgression of novel resistance genes for stem rust into small grains, particularly wheat. Thus a limited number of genes are deployed in the wheat varieties grown over large regions of the United States (e.g. the southern Great Plains) and throughout of the world. A strain of P. graminis has been identified in Africa that is virulent on the majority of the wheat and probably barley cultivars grown in the eastern United States. A concern shared by both small grains researchers and stakeholders is that this strain will follow a similar migration pathway as that of Asian soybean rust or wheat stripe rust and enter the U.S. before wheat and barley breeders have had time to introgress effective resistance genes into commercially acceptable varieties. To complicate the issue further, the introduction of resistance to one disease rarely provides protection to other diseases and may even disrupt established resistance. For example, wheat breeders in much of the eastern U.S. have focused on developing resistance to FHB, an effort which has resulted in the release of several moderately resistant varieties in the past several years. Unfortunately this work has caused the erosion in the level of resistance to stem rust, putting wheat at an increased risk to this potentially devastating disease. In summary, the combination of a susceptible crop and little probability of the release of resistant varieties in the next decade places wheat production in much of the U.S. at risk to the potentially devastating impact of a major stem rust epidemic.
Increased emphasis on disease prevention and management will be needed to help small grain producers remain competitive in international markets, to assure an ample supply of high-quality grain for domestic consumption, and to minimize the impact of adverse environmental conditions on small grain production. Given the decline in overall support for research and extension activities related to diseases of small grains, individual states have fewer resources for either research on the diseases of small grains or to provide pertinent information for all diseases attacking these crops through the state supported extension programs.
The exchange of information and coordination of research and extension activities among small grain pathologists and individuals in related research programs in the region east of the Rocky Mountains will facilitate better management of small grain diseases. In addition to increased communication and collaboration among small grains pathologists of the eastern U.S., it is anticipated that this group will interact closely with members of the WERA97 (Diseases of Cereals) on common diseases of concern. The groups have recently held joint meetings (e.g. 2006) and have planned joint meetings for the next several years (2007 and 2008).
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