Managing low-quality wheat seed following a season with severe Fusarium head blight (head scab) infection
The 2018-19 wheat harvest was affected by severe Fusarium head blight (head scab) in eastern and central Kansas, which can affect the quality of the seed for the next growing season. A direct consequence of head blight is a decrease in test weight (which is a measure of kernels’ volume weight or bulk density), as well as decrease in percent germination due to chalky, infected wheat kernels (Figure 1).
Figure 1. Chalky wheat kernels (thumbstones) resulting from severe infection of Fusarium head blight. Photo by Erick DeWolf, K-State Research and Extension.
While many of the severely diseased kernels are removed by the combine during harvest, seed producers in Kansas are reporting up to 40% cleanout this year to bring seed wheat to acceptable test weight standards (seed wheat should have a test weight above 57 pounds per bushel for adequate germination under a wide variety of conditions). This means that producers who stored grain on-farm and are planning to simply plant seed straight out of the bin might be in trouble. Especially this year, there is a need to pursue appropriate seed cleaning, and also to consider a fungicide seed treatment. K-State research conducted in seven locations during 2018-19 showed that improving seed quality through different seed cleaning methods leads to better stand establishment and grain yield even, in a season when Fusarium was minimal (Figure 2). Therefore, the benefits are potentially much larger this year when disease is severe.
Figure 2. Effects of seed cleaning method on wheat stand establishment (upper panel) and grain yield (lower panel). Data summarizes a study conducted in seven locations (Ashland Bottoms, Belleville, Colby, Hutchinson, Leoti, Manhattan, and Mitchell) during the 2018-19 growing season. Graphs by Romulo Lollato, K-State Research and Extension.
Seed with test weight slightly lower than 57 lbs/bu 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.
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-soil contact. Getting good seed-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 1.5 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. See the accompanying article in this issue of the eUpdate for more information.
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 7 to 14 days once the seed-testing lab receives the sample. The variation in the turnaround time depends on the need for pre-chilling treatment prior to the germination test. The need for pre-chilling typically ends around Labor Day weekend. The cost of testing at the Kansas Crop Improvement Association (KCIA) is $17.00 for the standard warm germination test. Growers or others can contact KCIA by phone at 785 532-6118, or by email at firstname.lastname@example.org.
On-farm germination tests may be an option for growers who do not have time to have seed evaluated by a seed-testing lab. This topic is addressed in an accompanying article in this eUpdate issue.
Romulo Lollato, Wheat and Forages Specialist
Erick De Wolf, Extension Plant Pathology
Eric Fabrizius, Seed Laboratory Manager, Kansas Crop Improvement Association