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Disease Concerns Necessitate Thorough Cleaning of Seed Wheat

In areas of the winter wheat belt, head scab has compromised seed quality.

The high incidence of Fusarium head blight (also known as head scab) in the central portion of the hard winter Wheat Belt can affect the quality of seed for the 2019-2020 growing season, Kansas State University reports in a news article published August 16. 

Head scab tends to decrease wheat test weight and can also decrease percent germination due to chalky, infected kernels symbolic of the disease. During the 2019 growing season, head scab was more pronounced due to the cool, damp conditions in the spring. 

While many of the severely diseased kernels are removed by the combine during harvest, certified seed producers in Kansas are reporting up to 40% cleanout this year to bring seed wheat to acceptable test weight standards, according to KSU. Seed wheat should have a test weight above 57 pounds per bushel for adequate germination under a wide variety of conditions. 

Authors Erick DeWolf, Eric Fabrizius, and Romulo Lollato – all KSU specialists – agree that producers who stored grain on-farm and are planning to simply plant seed straight out of the bin might be in trouble. Growers will need to pursue appropriate seed cleaning and also to consider a fungicide seed treatment. 

Seed with test weight slightly lower than 57 pounds per bushel may be acceptable to sow next year’s crop (if necessary), but when the low test weight is caused by Fusarium, the percent germination of the cleaned wheat seed might be well below acceptable levels despite acceptable test weights. In these cases, a fungicide seed treatment can help improve germination.

Take the Right Steps

Producers will want to take certain steps when sowing the next wheat crop to help increase the chances of getting a good stand. Low test weight seed usually germinates well, but seedlings tend to have lower vigor than seedlings from seed with higher test weights. Therefore, producers should take special care to try to get a good, uniform stand.

  • Drill speed. Using a drill speed of 5 mph or less will help ensure that the seed is placed down in the seed slot and that the seed slice is closed and firmed properly, making for good seed-to-soil contact. Getting good seed-to-soil contact will help the seedlings develop a good primary and secondary root system. Also, when drill speeds are too fast, the openers tend to ride up at times, resulting in a planting depth that is shallower than intended.
  • Seeding depth. All wheat should be planted at the proper depth for best stands. But it is especially important that low test weight seed is not planted too deeply, since this seed has low emergence vigor to start the growing season. It is equally important not to plant too shallowly. Shallow-planted wheat often has more difficulty establishing a good root system in the fall than wheat planted at the proper depth, and this can be an even greater problem when using low test weight seed. Plant low test weight seed 1 to no more than 1½ inches deep.
  • Seeding rates. Usually, the lower the test weight, the more seeds there are per pound. Producers who use a planting rate based on pounds per acre should not adjust their seeding rate when planting low test weight seed. They will end up planting more seeds per acre, but emergence is often somewhat lower with low test weight seed, so the stand should come out about normal. If the cause of low test weight includes fungal diseases such as Fusarium head scab, which decrease wheat germination rate, an increase in seeding rate may ensure a good and uniform stand.
  • Seed treatments. Fungicide seed treatments may improve germination or seedling vigor of low test weight seed and protect against certain diseases. 
  • Seed cleaning. Producers should make every effort to have their seed cleaned as thoroughly as possible to remove scabby kernels and shriveled seed. This may help increase the test weight and improve emergence and seedling vigor (Figure 2). Adjusting the settings during seed cleaning to blow lighter seed away can add 1 to 2 pounds to the seed lot's test weight by removing the small kernels. However, if the majority of the kernels are lighter and shriveled, the potential of gaining much test weight is limited, or the cleanout percentage is high.
  • Germination testing. This year, it would desirable to have the seed germination evaluated by a seed-testing lab to ensure a proper stand. The turnaround time for this type of testing is generally seven to 14 days once the seed-testing lab receives the sample. The variation in the turnaround time depends on the need for prechilling treatment prior to the germination test. The need for prechilling typically ends around Labor Day weekend. Contact your state crop improvement association for more details.

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