Seed-borne diseases to consider before using saved seed
This season there were more phone calls than normal related to loose smut of wheat. Loose smut would have been quite easy to see in the field at heading and early grain fill stages of growth. The kernels on infected heads are replaced with masses of powdery black spores. So the heads have a very obvious, black, powdery appearance. These spores are eventually dislodged by wind and rain, so later in the season the smutted stems are less evident and only the bare rachis will be left. Spores produced on smutted heads are wind carried to adjacent plants in the field and infecting through the flowers. The fungus that causes loose smut survives within the embryo of wheat seeds. Infected seed does not show visible symptoms and will germinate normally. However, if infected seed is planted, the plants growing from those seeds will be infected and develop smutted heads the next season. If seed from a field that has a “small” amount of smut in one season is used for seed, the field planted with that seed may have a substantially higher level of smut. Loose smut is best controlled by planting either disease-free seed or using the proper rate of a systemic fungicide seed treatment labeled for the control of loose smut.
Fusarium head blight or scab infection may result in shriveled and shrunken kernels, lightweight bleached or tombstone kernels or kernels that have a pinkish cast or discoloration. Lots with high levels of scab may have lower germination rates. The fungus that causes scab can also cause a seedling blight of wheat. If scab infected seed is used for planting, seedling blights and stand establishment problems may occur. Management of Fusarium seedling blight is through the planting of disease-free seed or a combination of thoroughly cleaning the seed lot, having a germination test run, adjusting the seeding rate to compensate for germination rate and using a fungicide seed treatment effective against seed-borne Fusarium or scab.
If any of the diseases covered in this article were present in a field this past season, it would be prudent not to use seed from that field for planting this fall. If seed must be used for planting is should be thoroughly cleaned to remove all shriveled, shrunken and lightweight kernels. A germination test would be recommended. For Stagonospora, loose smut and Fusarium head blight a fungicide seed treatment may be necessary. A number of fungicides are labeled for use as seed treatment fungicides on winter wheat. These seed treatment fungicides protect germinating seed and young seedlings from seed-borne and soil-borne pathogens. Seed treatment fungicides will not improve germination of seed that has been injured by environmental factors and will not resurrect dead seed. A correct assessment of the cause of poor seed quality or poor germination rates is the first step in deciding if a seed treatment fungicide is necessary.
Fungicide seed treatments for winter wheat are included in the 2013 Pest Management Guide: Corn, Grain Sorghum, Soybean and Winter Wheat, Extension Publication M171. Printed copies of this bulletin are available from the Extension Publications Distribution Center, 2800 Maguire Blvd., Columbia, MO, 573-882-7216 or on-line at http://extension.missouri.edu/p/M171 through MU’s Extension Publications.