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Disease Management Under Wet Conditions

Heavy rains and snow melt, in many areas, have resulted in saturated or ponded soils. The condition of winter cereals in such soils will be variable, depending on stage of crop development, depth of water, and length of exposure to ponding. For spring-seeded small grains, seed treatments should provide some protection from seed rot and seedling blight fungi for two to three weeks after planting. However, seed treatments aren't going to provide much benefit if the crop is sitting under water for an extended time. Long exposure to ponded water results in a lack of available oxygen (anaerobic conditions) for germinated plants whose roots needs to 'breathe'.

Cereal plants can take some short-term ponding (1-2 days) or flooding, as long as temperatures remain cool, but at higher temperatures, their survival rate decreases. Decisions on replanting should not be made until the soil is dry enough to determine crop condition.

Early Season Leaf Disease Control In Wheat

Tan spot and Septoria leaf blotch are prevalent in some fields of winter wheat in Manitoba. Start scouting early for these leaf diseases in winter wheat and spring wheat. Bear in mind that these problems may not be as severe as they seem to be at first glance. The majority of yield loss occurs when severe disease development occurs on the flag leaf and not when wheat is in the seedling stage. The risk of leaf diseases developing is greatest in fields that were planted to wheat in the previous year. Both winter and spring wheat will support the pathogens. Tan spot and Septoria leaf blotch are caused by fungi that overwinter on crop residue. They produces spores during wet periods in the spring. As little as six hours of moisture on the wheat leaves is needed for tan spot infection.

No-till fields recropped to wheat or no-till fields with heavy stubble remaining from two years ago also pose a risk of tan spot and Septoria leaf blotch. Fungicide may be applied to the crop at about the 5-leaf stage. A fungicide application at this growth stage is intended to slow the progress of the disease and prevent new infections for a period of time. The crop should be monitored through the season and, if a second fungicide application is needed, it should be applied at the flag leaf stage. Be sure to confirm the disease before applying a fungicide for disease management. As the crop approaches the flag leaf and early heading stage it should be re-scouted and a decision made as to the advisability of applying a fungicide.

Recommendations for stage of application and rates for recommended fungicides are included in the Guide to Field Crop Protection.

Summary Of Risk Factors And Guidelines For Fungicide Use

Not all fields are at the same risk of disease. A foliar fungicide applied to a wheat crop at the seedling stage may be warranted if: yield potential is high (>50 bu./acre); wheat is seeded into wheat stubble (especially under reduced-tillage); and environment is favourable for disease. A second scouting is recommended at the time of flag leaf emergence.

Late seeding of some cereal crops, increases the risk of exposure of these later maturing crops to rust spores. Leaf rust can cause damage to certain spring wheat varieties A complete listing of variety reaction to leaf rust is included in the publication Seed Manitoba. You may also wish to keep close track of leaf rust development on the wheat crops to the south as the season unfolds.

Barley Yellow Dwarf Virus (BYDV)

Late planted spring cereals may be subject to high aphid populations while the plants are still in the early growth stages. This makes them more susceptible to BYDV, a disease that is carried by aphids.

For further information, contact your GO representative.


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