To Spray Or Not To Spray?

Head Scab Forecasting System Click here to enlarge

Most of our wheat is nearing a time when a decision must be made –

To spray or not to spray?!  

Fungicide costs can range from $12 to $18 per acre plus application cost.  Today’s new crop wheat is hovering around $6.20 per bushel.

All of the wheat fields that I have looked at are showing no signs of disease pressure.  The head scab forecast system is showing a very low chance of scab and the 6 – 10 day precipitation outlook is for below normal rainfall and mild temperatures.  These factors are not conducive to disease development.

Below are additional thoughts from Dr. Pierce Paul and Dr. Kelley Tillman from this week’s C.O.R.N. Newsletter.

Fungicide and Insecticide at Flowering: Is This Really Warranted?

The wheat crop is flowering or will soon begin to flower in southern and central Ohio. Flowering will continue in the northern half of the state over the next two weeks. This is the growth stage as which the crop is most susceptible to infection by Fusarium graminearum, the fungus that causes head scab. Consequently, questions are being asked about applying a fungicide at flowering to control head scab, and at the same time, mixing in an insecticide to control cereal leaf beetle. According to the scab forecasting system (, the risk for head scab development has been low across the state over the past week. This is likely due, at least in part, to the cool, relatively dry conditions we have experienced across most of the state. The extended forecast suggests that dry (rain-free) conditions will persist over the next week or so.

Warm and consistently wet or humid conditions are required for head scab to develop. In fact, humid/wet conditions are also necessary for the development of most of the other economically important diseases of wheat such as SeptoriaStagonospora, and rust. When conditions are as consistently dry as they have been over the last few weeks, fungicides are not warranted. However, do continue to monitor the weather, and if it begins to rain, use the scab forecasting system to determine if the risk for scab is increasing as the crop continues to flower in the northern half of the state.

We specifically do not recommend tank-mixing an insecticide with a fungicide application if the insect populations do not legitimately warrant it.  Not only will it kill pollinators, but it also can eliminate the beneficial parasitic insects that attack cereal leaf beetle.  Insecticide is warranted for cereal leaf beetle control if there are 3 larvae per stem up to the boot stage, followed by a threshold of 1 larva per stem or flag leaf at boot stage and thereafter.  As the wheat begins to mature and grain fill has progressed, the need for spraying diminishes as it will not provide a return on investment.

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