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Scab: The Ninth District's agricultural plague of the '90s

Everyone knows farmers are struggling with low prices and slowing markets due to the Asian economic crisis, but farmers in parts of the Ninth District face the greatest threat from crop disease

November 1, 1998


Edward Lotterman Agricultural Economist
Scab: The Ninth District's agricultural plague of the '90s

What does Ireland have in common with eastern North Dakota and northwestern Minnesota? If your answer is rugged seacoasts and a marine climate, you need to retake geography. A guess of peat bogs would be correct for Minnesota, but not for its neighbor to the west. The correct answer: Both Ireland and parts of the Ninth District have had their agricultural economies devastated by microscopic fungi.

Comparing Ninth District farmers' struggle with scab of wheat and barley to the great Irish potato famine may be overdoing it. The phytophtera blight that devastated successive Irish potato harvests during the 1840s caused the starvation of thousands of people and one of the greatest human migrations in history. Nevertheless, for Minnesota and North Dakota farmers who have seen their crops devastated by the Fusarium head blight (scab) from 1993 through 1998, the epidemic is a major problem. While it has not caused death for anyone, it is credited with forcing migration on hundreds of people. The scab epidemic is also a problem for businesses in rural areas that store or transport grain or that simply depend on spending by farmers.

While it is difficult to estimate the exact economic cost of scab damage, one plant scientist argues that it is the most costly plant disease outbreak in the history of the United States. One estimate suggests it has cost district producers at least $1 billion so far in the 1990s. This figure is on the same order of magnitude as the 1997 Red River Valley spring floods, which attracted the attention of news media across the nation; however, most people, even in the Ninth District, have heard little about scab or its effects on the region.

Head blight of wheat and barley is nothing new. The United States experienced severe epidemics in 1917 and 1919, and again during the 1930s. An outbreak in South Korea in 1963 threatened starvation in some areas. Canada, Japan and Argentina have all experienced severe losses at various times in this century, and China has lost over a million metric tons of output in a single year.

But while scab did occur in the Upper Midwest at various times, it historically was more common in eastern and southern winter wheat areas as well as in areas with more than 20 inches of rainfall and where corn is produced. This changed abruptly in the 1990s.

There were localized outbreaks of scab in west-central Minnesota and eastern North Dakota in 1991. Some areas were hit again in 1992, and the wet conditions that prevailed in the fall of that year were propitious for a virulent epidemic that broke out in 1993. Yield losses in three Ninth District states-South Dakota, Minnesota and North Dakota-and in the Canadian Province of Manitoba were extensive. One expert estimated lost production of more than $1 billion. Losses in terms of bushels were the greatest of any outbreak in U.S. history and about 10 million acres were affected to some extent. Since North Dakota only plants some 20 million acres to all crops in a year, and Minnesota somewhat over 30 million, the magnitude of the outbreak is apparent.

While 1993 was perhaps the worst, sizable acreages in North Dakota and Minnesota have experienced some degree of scab each year since. In many areas, 1997 was the worst since 1993, and renewed scab losses together with low wheat prices were the primary factors leading to very high levels of farm business liquidations in eastern North Dakota and northwestern Minnesota between the 1997 harvest and the 1998 planting season.

map showing areas of scab damage

Fortunately, losses in 1998 were less severe than in several preceding years. But scab micro-organisms are present in the soil of large acreages and extensive losses in 1999 and subsequent years cannot be ruled out. Ironically, lower world wheat prices lowers the dollar value of losses due to scab damage, so a given per-acre yield loss in 1993 caused a greater economic loss than the same level of damage in 1998. But for affected farmers, the combination of low prices and reduced yields is a double whammy. Net farm incomes in 1998 will be the lowest in a decade or more for many Ninth District crop farmers.

Kent Olson, an agricultural economist at the University of Minnesota, expects that members of extension service-affiliated farm business management associations may experience declines in net income over 140 percent, that is, from a positive $40,600 per year in 1997 to a negative $16,230 in 1998. This estimate is for farmers in corn-soybean areas affected only by low prices and unaffected by scab. Wheat producers in scab-affected regions are experiencing equity losses for the third to fifth year out of the last six.

While losses due to scab are large relative to wheat production in eastern North Dakota and northwestern Minnesota, they are not that large compared to overall U.S. and world wheat output. Thus, there is no increased price effect from the lower production to buffer the effects of lower yields. Ninth District producers get both barrels: poor yields in a low price year.

What are prospects for the future? Some observers are not optimistic. While fusarium spores depend on host plant material in the ground to survive over winter, relatively high levels of infestation cover large areas. If the right weather conditions occur in 1999 or following years, new outbreaks could occur. Although scab primarily hurts the yields of wheat, durum and barley, it can overwinter in residues of other small grains such as oats and in corn plant residues. Thus there are few alternative crops to which farmers can rotate to eliminate fusarium spores from their fields in only one crop cycle.

Some of the more pessimistic experts predict a long-term if not permanent change in cropping patterns in the northern Red River Valley, one that would lower the expected value of crop outputs and hence the price of crop land in the region. Others note that scab infestations have come and gone in other regions of the country. They argue that just as large and successive infestations grew as the result of an unusual multiyear weather pattern in the 1990s, a few years of weather that is hostile to the organism could nearly wipe it out in the region.

Government officials in Minnesota and the Dakotas have recognized the importance of the problem and appropriated substantial sums of money for controlling the disease. But there seems to be no simple solution after several years of work. "Breeding in resistance isn't easy," says University of Minnesota plant pathologist Ruth Dill-Macky, whose research program centers on scab. "There just are not many varieties of wheat that show appreciable resistance, and the structure and location of the resistance genes makes genetic engineering difficult. And the fungus can mutate and get around the resistance." Farmers can rotate to other crops that are not susceptible to scab and whose residues do not serve as a host to the spores. But alternative crops are limited, particularly in more northern areas with shorter growing seasons, and cash return per acre is generally lower than wheat or barley.

Cultural practices also play a part. In the past 20 years farmers have switched from so-called conventional tillage using moldboard plows to reduced or minimum tillage with chisel plows or springtooth cultivators. Moldboard plows turn crop residues under a deeper layer of soil, cover them completely, and leave little trash on the surface. This clean surface then becomes susceptible to wind and water erosion, which is one reason for the switch to alternatives that leave more cover. Indeed, soil and water conservation compliance provisions in farm price support legislation in 1985 and 1990 practically required reduced tillage in many areas. But moldboard plowing was much less favorable to the survival and new dissemination of scab spores. "They should have talked to some plant pathologists before everyone jumped on the minimum tillage bandwagon," says Dill-Macky.