Saturday, May 8, 2010

Powdery Mildew Update

As noted in Shawn's previous posting, the wheat growth stage is mostly around Feekes 7. Karen Lackermann, graduate student in plant pathology, continues to collect disease data in the winter wheat variety trials and has been paying particular to the powdery mildew situation this year. The levels of powdery mildew have been variable across trial locations, with the highest disease incidence being observed at Chilton. Even within sites, there is high variation in disease incidence and severity. For example, at Chilton, some varieties have 0% incidence and severity, whereas other varieties have higher levels with severity ranging from 5 to 20% on the flag-3 (three leaves below the flag leaf). On the flag-2 leaf (two leaves below the flag leaf), severity has been moderate in these varieties, ranging from 1 to 5%. No symptoms of powdery mildew were observed on the flag-1 (one leaf below the flag leaf) leaf.

As we move into flag leaf emergence at Feekes 8, pay particular attention to symptom severity on the flag-2, flag-1, and flag leaf. If the average number of pustules on the flag-2 leaf and the leaves above it is 5 or greater, a foliar fungicide may be warranted for control of powdery mildew. If symptoms are only being observed in the lower canopy, below the flag-2 leaf, it may not be economic to apply a foliar fungicide.