Fungicide seed treatments for wheat
Fungicide seed treatments are becoming an important part of wheat production in Kansas. Seed treatments may help with wheat stand establishment in certain situations, and greatly reduce the risk of problems with seed borne diseases such as common bunt, loose smut or flag smut.
Seed production fields are a top priority for fungicide seed treatments. These fields have a high value and investments in seed treatments here help prevent the introduction and development of seed borne diseases on your farm Due to the high value of the seed produced, even small yield increases can justify the use of seed treatments.
For grain production fields, seed treatment economics are less certain. Conditions favoring use of standard seed treatments in grain production fields include: 1) high yield potential fields, 2) seed saved from fields with even low levels of loose smut, common bunt, or Fusarium head blight last year, 3) field sown at low planting rates, or 5) planting under poor germination conditions, especially very early or late planting.
If planting late or into heavy residue, it’s probably a good idea to use a fungicide seed treatment, even on seed that has high test weight and good germination. Planting wheat late into cool wet soils often delays emergence, and reduces the tillering capacity of wheat seedlings. Plants with reduced tillering capacity may not be able to compensate for stand loss and maintain yield potential like earlier planted wheat.
There are many different seed treatments available for wheat. Although most seed treatment ingredients are fungicides, some will also contain insecticides. Each ingredient targets slightly different disease causing fungi or insect pests. Many commercial formulations are complementary combinations of ingredients that provide a broader spectrum of protection.
As mentioned earlier, the most important use of seed treatments is for the control of seed-borne diseases such as smuts and bunts. Loose smut control requires a systemic fungicide like tebuconazole or difenoconazole. Common bunt, sometimes called, “stinking smut”, can be controlled, very effectively, with most commercial treatments. Some regions of the state have struggled with these diseases in recent years. If you are planning to keep seed that is known to have or been exposed to common bunt, it is critical to use a fungicide seed treatment to avoid problems in the future. Loads of grain contaminated with common bunt or often rejected at the point of delivery.
Figure 1. Loose smut on wheat. Photo by Erick DeWolf, K-State Research and Extension
Figure 2. The brown colored head is mature wheat with symptoms of common bunt. Photo by Erick DeWolf, K-State Research and Extension
Most seed treatments do at least a good job of controlling seed rots and seedling blights. Scab and black point are two seed-borne diseases that can reduce seed germination. If a seed lot has either of these, it should be cleaned to remove all light test weight seeds and then tested for germination rate. If the germination rate is low (less than 90%), a seed treatment could help increase the germination rate.
Some seed treatments also offer limited control of fall-season foliar diseases. Tebuconazole and difenoconazole provide some protection against fall infections of powdery mildew, leaf rust, and Stagonospora nodorum leaf blotch. A seed treatment will not prevent the disease from becoming reestablished in the spring, and foliar fungicide applications may still be required. Producers must balance the possible benefits against the cost and the possibility of having leftover treated seed. Leftover treated seed can be avoided by using hopper box treatments or other on-farm application equipment. If seed is treated on-farm, pay close attention to thorough coverage of the seed. Incomplete coverage can reduce the efficacy for the seed treatment.
For more information, see K-State publication MF2955, Seed Treatment Fungicide Wheat Disease Management 2017 at: http://www.ksre.ksu.edu/bookstore/pubs/MF2955.pdf
Erick DeWolf, Extension Plant Pathology