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By the time you 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 (e.g., 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 but when they get really
out of control I reluctantly mix one tablespoon (half strength) of Sevin 50 Powder (that I have had for many years) in a gallon
jug of water and lightly dribble (in the late evening to reduce toxic effect on bees) on the buds and new foliage of just
those varieties that the beetles like the best. Soon we see the dead beetles lying on the ground.
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 an extra day for each 10 degree increase in temperatures
(i.e., temperatures in the 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 WEDNESDAY WORK DAYS at THORNDEN PARK; ask questions at your local society meetings;
and call your nearby helpful Consulting Rosarian.
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