|
Causal organism - Blumeria graminis
 |
 |
 |
 |
Mildew overwinters primarily as mycelium on volunteers and autumn-sown crops. The cleistothecia produced during late summer are resistant to cold and drying out, and they allow the fungus to survive for a time in the absence of a host. In the UK green plant material is nearly always available and cleistothecia are thought to be of secondary importance. In humid weather, cleistothecia release the sexually produced ascospores which can initiate autumn infections. As temperatures rise in the spring, dormant mycelium starts to grow and spores are quickly produced. These germinate over a wide range of temperatures, from 5 to 30°C, although 15°C is optimal with relative humidity above 95%. Free water inhibits spore germination. Under dry conditions, fresh spores can be formed in about 7 days. At the end of the season, volunteers and early autumn-sown crops may become infected, providing inoculum for the next years crop.
Importance
Late-sown winter wheat crops are often particularly prone to attack, especially when growing rapidly in the spring. Excessive nitrogen fertilisers also encourages the disease and mildew can be particularly severe in dense crops. The visual appearance of the disease usually outweighs its damage potential especially during the autumn and winter. In susceptible varieties yield losses can be high (up to 20%) and early control can be very important. However, the disease generally causes much smaller yield losses and late attacks (after flowering) on the flag-leaf and ear rarely cause significant losses in most varieties.
