Evaluate winter wheat seed before planting
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. Bacterial streak (leaf symptom) and black chaff (head symptom) were also a problem in scattered fields throughout the state. The bacterium which causes this disease is seedborne. 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.
Bacterial streak and black chaff are names for the same bacterial disease which produces symptoms on both leaves and heads. Water-soaked lesions may develop on young leaves. These develop into reddish-brown to brownish black streaks on the leaves. Glumes and awns brown-black blotches or streaks. Black chaff may be confused with glume blotch. Symptoms may not be evident on individual kernels but the bacterial pathogen can be seedborne. Since seed treatment fungicides are not effective against this bacterial pathogen, seed from fields which had bacterial streak and black chaff should not be used for planting.
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 seedborne Fusarium or scab (see accompanying table of wheat seed treatment fungicides).
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% 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.
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