Treating diseased or discolored wheat seed
By D. Bruce Bosley
Wheat seed quality and disease prevention are a concern for many Colorado growers this year. Low-test weight grain as well as shriveled or off color or black-tipped grain is causing their concerns. Some of these potential problems can be addressed with fungicide seed treatments. The relative usefulness of fungicide seed treatments will depend on the situation.
If seed has a test weight of 55 pounds per bushel or less, but no evident disease problem (black point, loose smut, or common bunt), will a fungicide seed treatment be of any benefit? This is a hard question to answer, but it is possible that a fungicide seed treatment can improve or protect seedling vigor under stressful conditions.
Many Colorado producers have seen black point on kernels in their harvested grain. This disease can reduce germination rates and affect seedling vigor.
We also had a few reports and at least one confirmed case of fusarium head blight (scab) in Colorado this season. Head scab is much more common in higher moisture and especially higher humidity wheat growing regions. It can also affect germination and seedling vigor. Unless you have confirmed fusarium, head blight in your Colorado field it is unlikely that you have it in your grain even despite our record precipitation received in June and July.
Pink seed has been found in some wheat samples. This inconsequential bacterial infection should not be confused with fusarium head blight.
Kansas research shows that in many years, fungicide seed treatments result in small differences in germination and stand establishment. However, fungicides can have a greater impact in years when head scab and black point are affecting the seed quality.
Because Colorado climate is normally much drier than that experienced in other wheat belt states, it follows that fungicide treatments are even more unlikely to improve stand establishment. However, this year's weather in eastern Colorado may induce some producers to decide to treat their wheat before planting this fall.
If seed has a low-test weight or is infected with scab, the first step should be to have it cleaned hard to remove the lightest and poorest quality seeds. Once the seed lot has been cleaned, the seed should be tested for germination. If the germination is still lower than desired, you will probably want to adjust the seeding rate to make sure you hit your target plant population and may also consider fungicide seed treatment to help improve germination.
Producers need to be especially concerned that saved seed may be contaminated with diseases like loose smut or common (stinking) bunt. If loose smut or common bunt were present in the field the small grain was harvested from, the grain should not be used for seed. If the wheat Ô¨Åelds were not scouted for these diseases, any saved seed has the potential to be infected with them. Treating saved seed with a low-cost fungicidal seed treatment (e.g. Dividend, Raxil-Thiram, or RaxilXT) can reduce this risk. RTU Vitavax-Thiram is a combination fungicide that is effective for reducing seedling diseases and may also provide some protection for loose smut and common bunt.
For a seed treatment fungicide to be effective, clean the grain before treatment and ensure thorough coverage of the grain with fungicide. Colorado State Extension recommends that grain known or suspected to have loose smut or common bunt be treated by a commercial seed treater. The fungicides, which are effective for controlling loose smut and common bunt, are normally applied using a slurry treatment method.
The most effective long-term solution to loose smut and common bunt is to plant certified, fungicide-treated seed.
Finally, always eliminate volunteer wheat and other grassy weeds in harvested wheat fields at least two weeks prior to fall winter wheat planting to reduce the chances of wheat virus infections. Farmers can further reduce the virus potential by planting later in the normal winter wheat planting timeframe. Early planted wheat has a much higher potential for virus infections.
Aphid seed treatments (e.g. Gaucho or Cruiser) can reduce infection risks for barley or cereal yellow dwarf viruses. However, there are no insecticide treatments effective for controlling the wheat curl mite that serve as vectors for wheat streak mosaic virus, high plains disease, and triticum virus. Late planting and eliminating volunteer wheat are still the most effective measures that farmers can use to avoid wheat virus disease infections.
Please contact me, Bruce Bosley, about this or other cropping systems or natural resource topics at 970-522-3200 ext. 285 at Sterling or 970-542-3540 at Fort Morgan.
Colorado State University Extension provides unbiased, research-based information about family and consumer issues, gardening, natural resources, agriculture and 4-H youth development. As part of a nation-wide system, Extension brings the research and resources of the University to the community. For more information, visit www.ext.colostate.edu.