No. 6/May 2, 1997
Soybean Seed Treatments
With the relatively warm weather we have throughout the state, the chances of seedling blights on soybeans is somewhat reduced. These blights tend to be more severe when germination and emergence is delayed by cool or wet conditions and are minimized when plants rapidly emerge. Although Phytophthora and Pythium require almost saturated soils to produce their infectious spore stage, Rhizoctonia and Fusarium fungi can be active in moderately wet soils and are always more severe when conditions stress the seedlings.
To control seedling blights, fungicide seed treatments offer an inexpensive method of helping to assure a stand free of gaps and skips due to seedling blight fungi. The treatments are of no value when seeds have been damaged due to improper harvesting (combines not adjusted properly), excessive handling, or improper storage. Even microscopic seed coat cracks can cause damage to seeds that cannot be offset by fungicide seed treatments.
Selection of a seed treatment depends upon the diseases present and the application method. Apron is specific for Pythium and Phytophthora and has no activity against Rhizoctonia, Fusarium, or other soilborne fungi. Seed treatments containing carboxin (Vitavax), thiram, PCNB, or TBZ (Agrosol), and some other compounds are more broad spectrum and offer protection against Rhizoctonia and similar fungi. These materials are available as individual treatments or as combinations.
Application methods should also be considered. Many producers prefer to have a dealer treat seeds, which usually results in a more uniform covering of the materials. However, the disadvantage of this method is that once soybeans have been treated, they can only be planted. They cannot be used for any other purposes, and dealers commonly do not allow them to be returned if they are not planted. Because seed treatments are also available as planter-box materials, it may be to a grower's benefit to have only a portion of the seed treated by the dealer and treat the rest at planting.
Planter-box materials have greatly improved since the early days of dusts that blocked monitors, did not adhere, and typically ended up treating more of the planter than the seed. Many of the commonly used seed treatments can be applied as slurries or liquids with minimal application problems. The major concern is not to add all seed to a box and then try to apply the treatment. Planter boxes should be filled not more than half full, and one-half of the materials added and stirred into the seed. Then add the rest of the seed and the seed treatment and mix again. This helps ensure proper mixing and a more even treating than if the total material is applied before the box is filled.
Seed treatments are available in many forms and contain a variety of active ingredients. The list below provides some examples of materials and the fungi they will control.
H. Walker Kirby, Department of Crop Sciences, (217)333-4424