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Cephalosporium Stripe Research - Considerations for Control
Winter wheat yields this year in portions of the Palouse region were reduced 25 to 50 percent or more because of a fungus disease called Cephalosporium stripe. Several factors are involved in the increase of this disease. The growing of highly susceptible wheat varieties in short winter wheat rotations appears to have built up high inoculum levels in some fields over the past few years. The disease is also quite dependent on winter weather conditions. Cold temperatures and lack of snow cover are conducive to soil frost heaving. This causes root injury allowing the fungus easy access into the plant.
STEEP researcher George (Bill) Bruehl, Washington State University plant pathologist, is one of the pioneers in Cephalosporiurn stripe research in the Palouse. His research on the disease began in the mid-1950's when the highly susceptible Brevor wheat variety became popular in the region. The disease was almost forgotten for two or three decades after Gaines and Nugaines became the dominant winter wheat varieties. Both varieties have moderate resistance to Cephalosporium stripe. The disease has recurred dramatically since the adoption of the higher yielding, but highly susceptible wheat varieties Hyslop, McDermid and, most recently, Stephens.
Bruehl emphasizes two important impacts of growing highly susceptible winter wheat varieties in short rotations where the disease is present. The obvious one is the yield loss that can be sustained in years that are conducive to the disease. Table 1 shows recent research results illustrating the yield loss of different varieties under several levels of added disease inoculum. The ''check" was also infected with Cephalosporium stripe so yields should be compared with variety trial results in your respective areas. The four varieties McDermid, Stephens, Hyslop and Brevor are the most susceptible and have the greatest yield losses with added disease inoculum. Test weight was also affected. For example, test weight of Stephens for the check, low, medium and high inoculum levels was 58, 47, 47 and 44 pounds per bushel, respectively.
Table 1. Yields of winter wheat in a Cephalosporium stripe nursery in the 1983-84 season at Pullman, WA.
1 Cephalosporium stripe was also present in the check so yield should be compared to disease-free variety trials. The plots were sprayed with Bayleton to control rust and Benlate to control foot rot.
The second impact of growing highly susceptible varieties when the disease is present is that the most susceptible varieties also generally produce the most disease inoculum for losses in future wheat crops. Bruehl contends this has been an important factor in the buildup of Cephalosporium stripe over the past few years. Table 2 shows the variety differences in weight of infected straw and percent of stems infected in the 1982-83 season. Three of the four highly susceptible varieties - McDerrnid, Hyslop and Stephens - also produce the highest weight of infected straw.
Bruehl recently completed a study to determine what influence the level of infected straw in the field had on the infection level of the following wheat crop. McDermid wheat was seeded on summer fallow Sept. 15, 1983. Table 3 illustrates the very small amount of inoculum (pounds per acre of infected straw) needed to produce large increases in plant infection if conditions are favorable for the disease and a highly susceptible variety is grown.
Table 2. Production of Cephalosporium stripe Inoculum by wheat variety in the 1982-83 season at Pullman, WA.
Table 3. Influence of the level of added Caphalosporium stripe infected straw on disease level of McDermid wheat in the 1983-84 season at Pullman, WA.
1Check was also infected with Cephalosporlum stripe.
The 1983-84 year was so conducive to Cephalosporium stripe that the check was also infested. With no added inoculum, 26 percent of total plant weight was infested. Possibly a small amount of diseased straw may have blown onto the check or a low level of inoculum remained from the winter wheat crop 2 years previous, With only 16 pounds per acre infected straw added, the disease level increased from 26 to 55 percent. An 81 percent disease level resulted when only 129 pounds per acre of straw was added.
Cephalosporium stripe survives on wheat straw until the
straw decomposes. Without the straw, the fungus spores survive only a few months in the soil. According to Bruehl, this is the reason rotations with spring grains, lentils, peas and other crops are so useful for control of the disease. At least 2 years of spring crops or spring crops and fallow appear necessary to allow sufficient time for straw decomposition and reduction of the fungus inoculum level.
The fungus enters the roots of wheat during late fall, winter and early spring. A major factor that accentuates infection appears to be frost heaving of soils that causes root injury where the fungus can enter the plant. Connie Love, working with Bruehl as a graduate student, found that in greenhouse studies where no wounding occurs, a few plants still became infected. This ability to enter a plant without wounding, though not causing a serious disease loss, may assist the fungus in surviving in years unfavorable for the disease. A few diseased plants can keep the fungus from dying out. Love's greenhouse studies also indicate that Cephdosporium stripe is favored by soil acidity. The increased use of ammonium forms of nitrogen fertilizer over the past couple decades may be creating more favorable conditions for the disease by lowering soil pH levels.
Cephalosporium stripe has alternate host plants that can increase or maintain the disease level in the rotation. One host is downy brome (cheatgrass). The widespread occurrence of this hard-to-control weed may also be a factor in the increasing Cephalosporium stripe problem, Winter barley is also a host of Cephalosporium stripe although yield losses from the disease are much lower than for winter wheat.
Delaying the seeding date helps to reduce the occurrence of Cephalosporium stripe. Fewer, shorter roots from later planting would result in fewer potential infection points. However, care must be taken in selecting a later seeding date. Seeding too late can reduce yields even though the disease infection was largely prevented.
In an effort to reduce the carryover of disease inoculum in infected wheat straw, some farmers have resorted to stubble burning. However, we have no assurance that this will reduce the disease level in the following wheat crop. The straw is never completely burned and, under conditions favorable for the disease, only a small amount of inoculum from infested straw is necessary for causing significant infections (see Table 3). For example, if a 95 percent bum is achieved on 4,000 pounds per acre infected wheat straw, 200 pounds per acre will remain. If a highly susceptible wheat is grown and the winter is favorable for the disease, this small amount could still be enough to cause significant yield losses. Effects of stubble burning on soil erosion, runoff and water storage must also be considered.
Tillage also helps to reduce the level of Cephalosporium stripe inoculum in the field by accelerating residue decomposition, consequently reducing the food supply of the disease. Tillage alone, however, is not likely to significantly reduce the infection level of the following wheat crop when conditions are favorable for the disease. Tim Murray, Washington State University plant pathologist, emphasizes that burning and tillage are only short term measures and will not totally control the disease. Primary importance is placed on:
Murray, who assumed much of Bruehl's research efforts after Bruehl retired in 1986, also has started a study of the influence of residue management practices on carryover of Cephalosporium stripe inoculum. The Cephalosporium stripe research has been partially funded by the O. A. Vogel Fund.
us: Hans Kok, (208)885-5971
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