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Strategies for Soilborne Disease Control in Winter Wheat
Management for control of soilborne diseases in winter wheat often seems confusing, contradictory and almost impossible with any single cropping system. Changing the seeding date, variety or tillage method to reduce the impact of some diseases can often increase damage from other diseases. To help Northwest producers improve control of their soilborne disease problems, R. James Cook, USDA-ARS plant pathologist and STEEP researcher at Pullman, WA, has outlined management strategies for several different precipitation areas and cropping programs.
Cook points out that some disease can be expected in virtually every wheat field every year. However practices and systems have been identified through STEEP and other research programs that can minimize all soilborne diseases likely to occur in any area. He stresses that the objective of any cropping system should be to produce crops sufficiently healthy so that they yield to the limit of the available water. As a general rule, the greater the amount of available water, the more critical disease management becomes.
In low precipitation, crop-fallow areas, water rather than disease is almost always the main yield-limiting factor. Consequently, practices that affect available water (tillage, residue management) have a major influence on yield. In the higher precipitation, annual-cropping areas, disease rather than water is commonly the major yield-limiting factor. Practices that affect diseases (seeding date, rotation, tillage) have a major effect on wheat yield.
Consideration in Annual-Cropping
Four major soilborne diseases occur on winter wheat in the annual-cropping areas of the Northwest. They are Cephalosporium stripe, take-all, Pythium root rot and Pseudocercosporella foot rot. The following two management strategies for control of these diseases are designed mainly for the higher precipitation (16 inches or more annually), annual-cropping region.
Management Strategies for Control Of Soilborne Diseases in 3-Year Rotations Under Annual Cropping
1. Use of a 3-year rotation, 2 years out of winter wheat,will control Cephalosporium stripe regardless of tillage practices. The two crops between winter wheat crops in this rotation can include spring crops or nonhost winter crops such as winter peas or winter rapeseed. Winter barley can perpetuate the disease even though barley yields are not significantly affected. Two years allows sufficient time to reduce the amount of disease inoculum below an economic level.
2. The crop preceding winter wheat should be a nonhost for take-all disease. Peas, lentils, rapeseed and garbanzos are examples of nonhost crops in the Inland Northwest. Potatoes, bean and alfalfa are examples of crops for take-all control under irrigation. Oats are commonly used for this purpose in the Willamette Valley. A single year of a nonhost crop is usually adequate to reduce inoculum of this pathogen to safe levels. Although effective against Cephalosporium stripe, two successive crops of spring barley or spring wheat can provide considerable inoculum for take-all in the following winter wheat crop.
3. Seed winter wheat early (e.g. September 15-20 in the Pullman area) to escape Pythium root rot. This allows the seedling to rapidly establish in warm, well-drained soil when Pythium is least active. If fall moisture is not adequate for early seeding, seed as soon as possible using the newest available seed treated with a fungicide for Pythium control. Recent research by Cook has shown that Pythium damage to germinating seeds and emerging seedings increases with seed age at later seeding dates. Early-seeded wheat may not need a seed protectant for Pythium and can probably be 1 or 2 years old since the warmer, dryer environment alone can usually control Pythium on seeds and seedlings. The availability of adequate mineral nutrition also increases resistance ardor tolerance to Pythium, take-all and other soilborne diseases, Fertilizer, especially phosphorus, should be readily available to the plant roots during early growing stages.
4. Consider treating the winter wheat with a fungicide the following spring to control Pseudocercosporella (strawbreaker) foot rot. Winter wheat seeded early in a 3-year rotation is likely to have vigorous, lush fall growth which is ideal for strawbreaker foot rot infection.
Management Strategies for Soilborne Diseases in 2-Year Rotations Under Annual Cropping
Growing wheat every other year (rather than every third) limits the effectiveness of some disease control options and requires special adjustments if the four major soilborne diseases can be controlled.
1. Rotate with peas, lentils or other crops which are non host for take-all (as under the 3-year rotation).
2. Seeding date should be delayed to reduce the risk of Cephalosporium stripe. Although tillage is not needed for control of Cephalosporium stripe in a 3-year rotation, some tillage for incorporation of the winter wheat residue should be considered in a 2-year rotation to speed residue decomposition and reduce inoculum carryover. No-till or minimum tillage methods can still be used for seeding winter wheat after the nonhost crop.
3. Use current-year seed and treat with a fungicide to protect against Pythium infection of seed embryos. This will help to reduce the chances of Pythium damage associated with delayed seeding.
4. Plant the most Cephalosporium stripe-tolerant variety available. Stephens is the most susceptible. Lewjain is the most tolerant. Check with the County Extension Agent in your area for disease resistant ratings of other area varieties.
5. Apply a fungicide (if necessary) early in the spring to control Pseudocercosporella foot rot.
Management Strategies for Control Of Soilborne Diseases in a Wheat-Fallow Rotation
Fusarium foot rot, Pseudocercosporella foot rot, Cephalosporium stripe and snow molds are the most important soilborne diseases of winter wheat on fallow in the Northwest.
1. To reduce the incidence of Fusarium foot rot, apply only the nitrogen fertilizer needed to achieve the yield potential for the available water. Over-fertilization resulting in early water stress is the most common factor associated with Fusarium foot rot in the fallow region.
2. Seed in late August-early September where snow mold is a problem. A larger, more vigorous plant generally has better survival of snow mold, Varieties such as Sprague and John have some snow mold tolerance.
3. Where necessary, a fungicide should be applied in early spring to control Pseudocercosporella foot rot associated with the early seeding date.
4. If Cephalosporium stripe is a problem, include a spring cereal or other nonhost crop in place of winter wheat (e.g. winter wheat-fallow-spring cereal-fallow), Cephalosporium stripe occurs in the wheat-fallow rotation in intermediate precipitation areas (14 to 18 inches), but rarely in low precipitation areas. This longer rotation also helps control winter-annual, grassy weeds such as downy brome and jointed goatgrass.
us: Hans Kok, (208)885-5971
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