Once again we have had an unusual growing season with cooler temperatures and in some areas more moisture during the wheat heading/flowering stage. Due to the moisture, we have seen some scab issues in the hard red spring wheat received so far. With over 170 samples of new crop spring wheat from SD and MN tested to date, over 37% has exhibited germination rates below 80%, and over 60% of the samples have below 90% germination. Germination ranges that we have seen to this point have been from 45% - 99%; many of these have been from “uncleaned seed lots”.
Scab: Disease profile
Scab, also known as Fusarium head blight, head scab, or pink mold, is a fungal disease caused by Fusarium spp. that can attack spring and winter wheat as well as other small grains, and it can even infect many other grass species. Visual symptoms of infected seeds are not always present on seeds or grain, but usually scab-infected wheat kernels are shriveled, discolored with a white, pink, or light brown scaly appearance. These kernels are often referred to as “Tombstones”. Infection of scab can also lead to production of mycotoxins in the seed. The most prevalent one, “Vomitoxin” (also known as DON) is often tested for as it can cause problems for grain utilization due to limits for human consumption, flour quality for bread making, and problems in the beer brewing industry.
Spring wheat seed producers will need to more rigorously condition seed with a gravity table to remove lightweight scab-infected kernels, and should use fungicide treatments on spring wheat seed. Planting seed lots that have scab damage does not, however, mean you will have scab next year. The development of the disease depends on environmental conditions at flowering, the crop residue the wheat is planted into (corn, sorghum, wheat and millet pose the most risk), and the level of scab resistance in the wheat variety grown. For these same reasons, fungicide seed treatments will not prevent scab next year. Foliar fungicides offer about 60% control of scab.
Effects on Germination
Scab-infected seed, if not dead, will have lower vigor and be more susceptible to other field fungi when they germinate in the soil, and will remain vulnerable to infections in the seedling stage. Infected seeds/seedlings can reduce germination percentages in germination testing because of secondary infections. To reduce these infections and obtain a more accurate test the lab spreads out seeds/seedlings by planting eight 50-seed replications. From past experience this practice can increase the rate of normal seedlings (have all essential structures for growth) by up to 10% versus the normal planting of 4 replications of the 100 seed method.
Treating Your Seed
Another option that growers should be using is a fungicide seed treatment. Using a seed treatment will not bring dead seeds to life, but will protect seeds and seedlings from early season fungal infections. It will also suppress surface-infected Fusarium from growing during the germination test and prevent infection of the seedling, thus allowing that seedling a chance to grow into a productive plant. A fungicide treatment will usually increase germination of infected lots on average at least 10% higher over a standard (4 reps of 100 seed) germination test. To compare potential germination benefits of seed treatment the SDSU Seed Testing Lab offers a treated germination test (using Raxil™ or Stamina/Charter F2™ or CruiserMaxxVibranceTM) along with the standard (untreated) germination test. There are several effective fungicide seed treatment products on the market and the lab does not endorse one over the other. For treatment products and options contact your SDSU Extension Field Specialist, your crop consultant, local Cooperative, or the Extension Plant Pathologist Emmanuel Byamukama).