Rosette or double blossom
is an extremely destructive disease of blackberries. The thornless varieties
which were developed at the University have typically been fairly resistant to
the diseases. That doesn’t mean you’ll never see it, but it is not as
life-threatening as it would be on other varieties. Rosette is usually more of a
problem in areas with a high concentration of wild blackberry plants. While
Benlate ( Benomyl is the active ingredient) can give you limited control for the
next season, if you spot the disease, your best method of control is sanitation.
Cut out the infected canes and destroy them. Sterilize your pruning shears after
each cut to prevent spreading the disease. Hopefully, this will be an isolated
problem.
Last year our Navajo
thornless blackberry plants developed what our County Agent decided was rosette.
He recommended spraying with Benlate. I was unable to find this in our area. We
have twenty plants, and a neighbor has 60 plants. Since the University of
Arkansas developed the Navajo plants, have they recommended a spray to control
rosette?