Winter Wheat Disease Update

DR. LAURA SWEETS

COLUMBIA, MO.
   According to the July 6, 2015, Missouri Crop Progress and Condition report put out by the USDA, National Agricultural Statistics Service, Heartland Regional Field Office, winter wheat harvest was 68 percent complete, 20 percentage points behind the 5-year average. With the continued wet conditions through much of the state, the quality of the wheat still in the field is deteriorating. Fusarium head blight or scab was widespread in most regions of the state this season and its impact on yields and grain quality is being seen as fields are harvested and grain taken to elevators. The wet conditions and high humidity have also led to widespread occurrence of “black wheat.” Both of these diseases were covered in IPCM alerts earlier this season.
   Now there are questions related to saving seed from this year’s crop for seed for planting this coming fall. With the high levels of scabby kernels and the overall lower quality of grain, this is not a good year to consider saving seed for planting. But if this alternative is still being considered there are certain steps to take in making the decision of whether or not to use saved seed for planting. The remainder of this article focuses on evaluating winter wheat seed quality for possible planting use.
   Fusarium head blight or scab was widespread, and in some fields severe, this season. The fungus which causes this disease may infect kernels and can affect stands if infected seed is planted. If wheat is going to be saved for seed, this is certainly a year to pay careful attention to the quality of seed being saved. Initial reports from both the Missouri Seed Improvement Association and the Missouri Department of Agriculture indicate lower germination test results on wheat from this year's crop from some regions of the state. Visibly fungus infected seed are common.
   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.
   Because scab can decrease germination, a germination test may be especially useful in determining if a particular lot should be used for seed. The minimum germination rate for certified seed is 85 percent germination. It is possible that lower germination rates might be successfully used for seed if the seeding rate is adjusted to compensate for the low germination rate. But this can be risky, especially if weather conditions at and after planting are not favorable for germination and emergence. Fungicide seed treatments can provide some benefit but they cannot resurrect dead seed.
   If seed from a field that had Fusarium head blight or scab is being considered for use as seed this fall, it is important to get an accurate germination test and use this information in deciding whether or not to use the lot for seed, whether the seeding rate will need to be increased and whether or not to apply a seed treatment fungicide.
   Before submitting a sample for a germination test it is important to thoroughly clean the seed. The wheat seed should be cleaned to remove small and damaged seed and to eliminate weed seeds. With the amount of scab is some lots this year, thoroughly cleaning a lot may clean out 25-30 percent of the seed in the lot. But a thorough cleaning will give more reliable germination test results and removing small and damaged seed will not only aid in crop establishment it will also provide a more uniform wheat seedling stand. Removing small and damaged seed will also increase the thousand-kernel weight (TKW), which serves as a measure of seed quality. Wheat seed lots with TKW values greater than 30 grams tend to have increased fall tiller number and seedling vigor.
   The next step is to perform a germination test. Germination tests can either be completed at home or by sending a sample to the Missouri Seed Improvement Association or the Missouri Department of Agriculture.
   A home test can be performed by counting out 100 seeds and placing them in a damp paper towel. Place the paper towel into a plastic bag to conserve moisture and store in a warm location out of direct sunlight. After five days, count the number of germinated seeds that have both an intact root and shoot. This will give the grower an estimate of percent germination. It is important to choose random seeds throughout the entire seed lot and conduct at least five 100 seed counts.
   The Missouri Seed Improvement Association performs germination tests. The test requires one pound of seed and costs $14.25. For details email MOSEED@AOL.com or check the Missouri Seed Improvement Association web site at http://www.moseed.org/.
   The State Seed Control Laboratory at the Missouri Department of Agriculture also performs germination tests. The test requires one pint to one quart of seed. From June 1 through August 31 tests are free for Missouri farmers but between September 1 and November 1 there is a $12.00 fee per sample and a limit of four samples per farmer. Information and a submission form can be obtained on the Missouri Department of Agriculture web site, http://mda.mo.gov/plants/seed/ and then clicking on Submitting Seed Service Samples.
   If germination is below 85 percent it is important to increase the seeding rate to compensate; however seeding any wheat with a germination test below 80% would not be recommended.
   The next step is to decide whether a fungicide seed treatment is 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 seedborne and soilborne 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 2015 Pest Management Guide: Corn, Grain Sorghum, Soybean, Winter Wheat, Rice and Cotton, 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 online at www.extension.missouri.edu/p/M171 . ∆
   DR. LAURA SWEETS: Extension Associate Professor, Division of Plant Sciences, University of Missouri