Fungicide seed treatments for wheat
Fungicide seed treatments may help with wheat stand establishment in certain situations. For seed production fields, a systemic seed treatment is highly recommended to help keep seedborne pathogens such as bunt and loose smut out of seed stocks. 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 field, 2) seed saved from field with loose smut, bunt, or Fusarium head blight last year, 3) expensive seed, 4) low planting rates, 5) planting under poor germination conditions, especially very early or late planting, or 6) poor quality or old seed.
If planting that 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. While there may be a higher initial cost for using clean/certified, treated seed, the cost is almost always exceeded by the benefit in yield.
There are many different seed treatments available for wheat. Although most seed treatment ingredients are fungicides, some will also contain lindane and imidacloprid as insecticides. Each ingredient has certain strengths and weaknesses which may depend on the particular rates used. Many commercial formulations are complementary combinations of ingredients in order to provide a broader spectrum of protection.
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 carboxin, tebuconazole, or difenoconazole. Common bunt, sometimes called, “stinking smut”, can be controlled, very effectively, with most commercial treatments. Some elevators around the district have reported affected wheat with common bunt in recent years. If you are planning to keep your seed that has been confirmed with common bunt, seed treatment is critical.
Most treatments do at least a fair 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 improve stand establishment. Several insecticide products are available if wireworms are expected to be a problem in stand establishment.
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.
Triadimenol, tebuconazole, and imazalil can shorten the coleoptile, so avoid deep planting with these treatments.
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. If seed is treated on-farm, pay close attention to thorough coverage of the seed.
For more information, see K-State publication MF2955, Seed Treatment Fungicide Wheat Disease Management at: http://www.ksre.ksu.edu/bookstore/pubs/MF2955.pdf
Erick DeWolf, Extension Plant Pathology