The winter wheat crop is entering a critical growth phase, the time period of 25 to 30 days before heading and ten days after. This is when the number of kernels are being determined. The are many factors that influence this growth phase . The top four are nitrogen supply and uptake soil moisture, temperature and plant health.
The major management focus is on plant health in particular protecting the flag leaf and the one below it called the penultimate leaf. These two leaves account for 70% to 75 % of the final yield. It is important to scout the field to check on the incidence and severity of foliar fungal pathogens moving up in the canopy.
The application of fungicides should be made to protect the flag and penultimate leaf. This is referred to as T2 timing and the next important growth stage is at flowering time referred to as T3 growth stage.
Recent moderate temperatures and rainfall can be supportive of fungal pathogen infection. The next 10 days will require a close watch on the wheat crop to check on any disease progression.
Perhaps the most critical growth stage is T3. The main purpose of a fungicide application at this stage is to reduce the incidence and severity of Fusarium Head Blight infection which contributes to Fusarium Damaged Kernels (FDK) which is a grade discount. Secondarily the risk of mycotoxin DON is greater with a higher infection level which further reduces marketability of the crop.
The critical growth stage for observing the best time for protecting the heads is Zadoks 59 to 60. This is when 75% of the heads on the main stem have completely cleared the leaf sheath, we also call this day “0”. A T3 application for targeting Fusarium should be applied shortly after this on “day + 2” which is the beginning of pollination when anthers (flowers) are showing on the middle of the wheat head Zadoks 62-65. This is when most of the florets are open and when infection is most likely to occur.
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