Part 2, Section 5: Small Grains Pest Management
Small Grains Pest Management
DISEASES
Disease management is an important part of winter wheat production in Pennsylvania. The most common diseases in the Commonwealth are powdery mildew and stagonospora leaf blotch. Other diseases, such as Fusarium head blight (scab), barley yellow dwarf, and leaf rust can be severe, but fortunately disease epidemics occur only sporadically in our region. Many of these diseases can cause considerable yield losses if left uncontrolled. This ection describes some of the disease management strategies available for small grains in Pennsylvania.
Plant disease-resistant varieties
Planting disease-resistant varieties is the most effective and economical way to manage many diseases of wheat. Many wheat varieties that have a high level of resistance to powdery mildew, leaf rust, and wheat spindle streak virus are available. Varieties with a moderate level of resistance to Stagonospora leaf blotch and Fusarium head blight can also help to manage these diseases. Use the information provided by Penn State Cooperative Extension and seed companies to select varieties that have resistance to as many diseases as possible. However, be aware that disease reactions may change rapidly if new races of the pathogen develop. This type of “race shift” is most commonly reported for powdery mildew and leaf rust. Selection of disease-resistant varieties, when used in combination with crop rotation, appropriate planting date, and fungicide-treated seed, is an effective way to maintain consistently high wheat yields.
Scouting for disease
Monitoring wheat fields for disease is essential to identify fields that may need a fungicide application when growing susceptible and moderately susceptible varieties. Assess the average disease level on at least 40 tillers randomly selected from throughout the field. Fields should be checked for disease at flag leaf emergence (Growth Stage 8).
Fungicide applications
The upper leaves and glumes contribute the most to the wheat yield, and it is important to protect these leaves from disease damage. Fungicides should only be considered for susceptible varieties with a yield potential of 60 bushels per acre or more, and if weather forecasts indicate that conditions are likely to favor continued disease development. Disease thresholds and suitable fungicides for powdery mildew, Stagonospora, and leaf rust are provided in Table 2.5-9 and 2.5-10. Table 2.5-11 provides the estimated yield losses attributed to powdery mildew based on variety susceptibility and disease level.
Many varieties of wheat that are resistant to powdery mildew have been developed to have resistance to all races of the pathogen. This type resistance is not subject to dramatic failures when new races of the pathogen are introduced into a region. Varieties with this type of resistance will often develop low levels of disease, but that rate of development and severity of the disease is reduced.