Q How can we prevent or at least control rust on our hollyhocks? We have used several fungicides but each year our plants
suffer.
A. & R. K.-H., Willowdale
A: Many species of the mallow family are subject to infection by rust parasites. Hollyhock rust (Puccinia malvacearum) has limited their use as ornamentals, but there is hope, in an ounce of prevention!
Monitor your plants from the beginning of the growing season onwards. First thing in the spring make sure to clean up all debris around your hollyhocks to get rid of the overwintering spores on the leaf litter and dead stems.
Cultivate the soil surface to a depth of one to two centimetres so that it dries out well: this helps to keep the humidity low around the young leaves. At this early stage, the foliage and surrounding soil can be sprayed with wettable sulphur or dusted with sulphur powder. (Both should be available at your local nursery, garden centre, or drug store.) Sulphur powder is easily dusted onto plants using an old nylon stocking with a cup of dry sulphur in the toe, and shaking it lightly over the plant.
As the temperature keeps climbing and your hollyhocks start into more active growth, remove and destroy any leaves that show signs of rust. Then, re-treat with sulphur. In the early season be sure to check the plants two or three times a week since the new leaves develop rapidly and it's essential to treat them as soon as possible. Reapply as needed after rains and avoid watering over the leaves.
As the season progresses, keep an eye on your hollyhocks. As soon as the flowering is finished cut the plants back to the base. All spent parts should be gathered up (including seed pods and dead leaves) and destroyed -- that is, burned, or sealed in a plastic bag.
Q: My African violets have seemed healthy for years and always have lots of flowers. Recently, however, I've been noticing tiny pale yellow spots on the leaves that seem to run together in some places making the leaves look a bit translucent. Can you tell me what to do?
K.M., Rosedale
A: If this is the first time you are noticing these problems, I suspect that you've added a new plant or two to your collection lately. The new plant doesn't have to be an African violet, either.
What you have sounds very much like a spider mite problem. The mites cause the tiny yellowish spots by piercing the leaf and sucking the juice out of the cells. The spots run together when the feeding gets heavier.
Cyclamen mites also attack African violets but the other telltale sign they leave is harder, contorted leaves that are much hairier than normal.
Both kinds of mites can be easily controlled by inverting the plant in a container of room temperature water with liquid soap added. The ratio is 40 parts water to one part soap. Swish the foliage and crown of the plant gently around in the water to ensure coating all surfaces. Set the plant aside for five to 10 minutes, then rinse it completely with clear room temperature water. Shake gently to remove as much moisture as possible from the foliage. Place your damp plants in a bright, well-ventilated area to ensure that the leaves dry completely before evening.
This treatment must be repeated three times over a 10-day period to break the rehatch cycle of eggs on the plant. Monitor your plants regularly and re-treat only as needed, and soon your African violets should be as healthy as ever.
Ed Lawrence is chief gardener for Ottawa's official residences and host of a CBC Radio phone-in show. Send your questions to elawrence@globeandmail.ca