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Small Grains Disease Update

Weather conditions have been getting steadily warmer over the last week, routinely in the mid-80s° F. This trend is set to continue over the next week with temperatures reaching the low 90s° F. This unusually dry and warm weather is having a direct impact on the range and severity of diseases and plants reactions to other stresses such as herbicide drift and drought. With the majority of wheat in the end of milk and into the early dough stage, many plants are clearly showing evidence of heat stress. This heat stress is exacerbating other diseases that are not normally prevalent.

Stripe rust is still very evident across the state with high severity on spring and winter wheat in to the mid canopy. A number of fungicides will give good control of stripe rust provided they are applied before symptoms are evident on the flag leaf. Fungicide application will not cure already visible or latent infections. Although the warm temperatures will slow stripe rust development, cooler night time temperatures and the chance of stormy precipitation, will allow this disease to continue. If generic Folicur, Prosaro or Caramba were already applied at Feekes 10.51 to suppress scab, you can expect sufficient control for the remainder of the growing season for stripe rust.

Septoria species are also becoming prevalent in the west central portion of the state with low - mid severity on 20-50% in the fields scouted. Evidence of wheat stem maggot is now appearing in the south-west of the state. Typical symptoms of damage caused by this insect are white or blasted heads which will produce no grain, while the rest of the plants looks normal. The head can easily be pulled from the plant to reveal the feeding damage.

Because of the weather, the risk of scab is likely to be very low over the next week. These same conditions are more conducive to stem rust and leaf rust may become more evident, especially in the southern part of the state.

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  1. What else is causing white heads? It looks like it could be a type of late root rot. Any other reports?

  2. In the SE portion of the state, small grains harvest has begun. We finished our barley harvest late last week (7/7, about 3 weeks ahead of normal) and are now seeing some yields from the barley and oat crop.
    I can report that our barley yields were in the upper forty's to lower fifty bushels per acre. While this is somewhat below what we would consider an average yield for this variety (Royal), the grain quality is good, with a bright and unweathered appearance and very good test weight.
    As Dr. Wiersma had noted earlier in the season, Barley Yellow Dwarf Virus infection was severe and widespread throughout Southern Minnesota. With very early planting dates (3/19), warm weather and timely moisture, the crop was quick to establish. The early crop establishment provided excellent opportunity for tillering. However, with unseasonable early season warmth, it is believed that aphid infestation brought about the BYDV infection. Other factors have contributed to additional stress conditions throughout the growing season, with some frost injury in April, and the lack of adequate moisture being among them.
    The initial oat yields have been variable. Growers have reported yields ranging from 75 to 95 bushels per acre thus far, with test weights ranging from 35 - 41 pounds per bushel. Many acres were treated with fungicide, which has maintained plant health and averted a severe rust infestation, however, Red Leaf was prevalent and may have resulted in a yield reduction. Also, excessive heat during the heading period resulted in kernel abortion on the lower portion of the grain head. This so-called "blasting" effect varies among varieties, likely based on heading timing, rather than the variety itself, and may have negatively affected potential yields, varying from 10 to 30 percent in kernel loss from field to field.


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