The role of seed treatments in wheat disease management
This is the time of year that wheat producers are finishing their seed purchases and making decisions about whether or not to use a seed treatment. There are both fungicide and insecticide seed treatments available, which can be used alone or in combination.
Fungicide seed treatments
As the research results of fungicide seed treatment trials done in Kansas and throughout the U.S. are evaluated, a few questions emerge that are worth discussing. 1) What is purpose of these seed treatments? 2) What value do they have for wheat producers in Kansas?
Think about these questions for a minute before you continue reading. Is your answer something like this: “The primary purpose of seed treatments in wheat is to reduce the risk that diseases and insects pests will affect stand establishment and the early stages of plant development.”
Based on the research reviewed, this is a true statement. In fact, seed treatment fungicides do increase stand by an average of about 10% under heavy disease pressure. The problem; however, is that these increases in stand don't always translate into a yield increase. In fact, research results suggest that in most years the yield improvement from seed treatments is generally less than 1%. Wheat has a tremendous ability to compensate for moderate losses of stand through increased tiller production on the remaining plants.
A closer look at the data indicates that occasionally there is a large yield response -- more than 20%. There must be some additional value beyond stand establishment that explains these large yield responses.
Fungicide seed treatments are one of the primary tools for management of seed-borne diseases such as common bunt (stinking smut) or loose smut. The fungi that cause these diseases survive in association with wheat seed and can build up to damaging levels in just a few years. If you have ever had loads of wheat rejected for stinking smut you know what “damaging levels” means.
Seed treatments are an effective way to prevent these seed-borne diseases from becoming a problem on your farm. Seed for varieties you intended to save for seed on your farm in coming years is a top priority for these treatments, because seed production has higher value than general production fields. This is to say, the cost of replacing the seed you grow yourself with all new seed is much higher than the cost of the seed treatment now.
Insecticide seed treatments
Seed treatment insecticides have a role in the management of barley yellow dwarf (BYD). Greenbugs and bird cherry oat aphids spread BYD and the most damaging infections generally occur when the virus is introduced into the plants early in their growth and development. The seed treatment insecticides such as Imidacolprid (Gaucho) or Thiamethoxam (Cruiser) can provide protection against aphid feeding in the fall and lower the risk of severe BYD.
The research results on these products indicate some situations where a yield response may exceed 20%. Unfortunately, this yield response is inconsistent among years. Why is this? In some years, the peak aphid activity occurs in the fall and the insecticides do a great job of preventing the aphid populations and spread of the disease. But if the aphids remain active during a mild winter or arrive in the spring, the insecticide is no longer effective.
Seed treatments have important role in wheat production in Kansas, a role that goes beyond stand establishment. The primary role of these products may be to manage seed-borne diseases and to reduce the risk of BYD. When it comes to BYD management, it is important to have realistic expectations. In some situations there will be a yield response large enough to make the practice worthwhile, but you may have to weather some years where the aphid population is active beyond the limits of the insecticide.
More information about production options and priorities for wheat seed treatments can be found in the recent K-State publication: Seed Treatment Fungicides for Wheat Disease Management 2012, MF2955 at your local county Extension office or at www.ksre.ksu.edu/library/plant2/MF2955.pdf/