By: Jim
Wagner, Consulting Rosarian
Late Summer Rose Care
By
the time you have read this article (early August), peak spring blooms are a
memory for another year; gardening enthusiasm may be on the wane; and we should
be thinking about the first phases of pre-winter care (making our roses as
healthy as possible to improve their winter survival). In going from a wet, cold
spring to a
dry, hot, and humid summer, it has been a real challenge trying to have nice
looking roses this year
Blackspot &
Powdery Mildew
Except
for the munching of Japanese Beetles on our more fragrant and/or lighter
colored roses and powdery mildew on a couple of varieties that are mildew
prone, our roses are still in good shape for mid-summer. However, the hot and
humid weather of
the past month has been ideal for blackspot and powdery mildew problems for
some people. Blackspot, as the
name implies, initially starts as small black spots on the surface of the lower
leaves of the bush. Then yellow
margins around these spots can extend to the whole leaf. In between sprayings,
we try to remove
any leaves that might show signs of this disease for disposal far away from our
roses.
It
seems that I have more questions on powdery mildew. This fungus likes the newer growth and buds near the top of
the bush and “innocently” starts out with slightly raised blister-like areas on
upper surfaces of the newer foliage.
Later, leaves become twisted and curled and then covered by white
spores. Some varieties (ie:
Heirloom and Touch of Class) are more prone to this problem. When I find a cane
or a group of canes
that are seriously disfigured, I sometimes sacrifice some of the future bloom
by cutting away the portion of the bush that is seriously disfigured and send
it onto the land of the unknown.
For
both blackspot and powdery mildew, regular 7 to 10 day applications of a
fungicide to both the top and undersides of the foliage will help control the
spread of these diseases. Some
people claim that they have used products that will totally eliminate these
problems after they have taken a foothold but I have not had this kind of
experience.
Japanese
Beetles.
Upon
our return from our NH trip we found that the buds, blooms and new foliage on
more fragrant roses like Fragrant Cloud and Olympiad and lighter
colored roses such as Chicago Peace and Sally Holmes were
badly chewed by the Japanese beetles.
Our preferred control for these beetles is hand picking them into a jar
of soapy water several times a day.
Nourishment
and Water
To
help the plants prepare for the upcoming winter, nourishment should be
slackened off this month. If you
use granular fertilizer (ie:10-10-10), I would make my last application no
later than early August. However,
one can still make use of
water soluble fertilizers but at about ½ to 2/3 strength during most of
August. And always, water
deeply (an inch or more at a time) several hours to a day before fertilizing or
spraying and increase the frequency of watering as the temperature rises.
An
unscientific approach that I like to
use is to increase the watering frequency by about 2 to 3 days for each 10
degree increase in temperatures (ie:
temperatures in their 60s and lower 70s – weekly watering should be OK;
mid- 70s to mid-80s - twice a week; and mid-80s and higher – three times a
week).
As
always, feel free to come to VOLUNTEER WORK DAYS at THORNDEN PARK; ask questions
at your local society meetings; and
call your nearby helpful Consulting Rosarian.
Rose Care,
Late-Summer - (07/19/02)
