The flag leaf application for autumn barley crops is predominantly
aimed at protecting the crop from attack by Ramularia leaf spot
(RLS) and leaf rust (pg 25). In wet years scald can also
remain a threat at this time.
RLS is a very aggressive disease, so applying fungicides at GS39,
when the flag leaf has just emerged, is very important to achieving
a good level of control. If the application is delayed, say to the
traditional “tooth brush” stage (GS49), control can be reduced.