Fall is a good time to reduce the risk of pest and disease problems next year. Your first goal should be good garden sanitation practices. Cut down any diseased plant material and remove and destroy debris on the soil around infected plants.
When roses are grown in fertile soil and receive the requisite amount of water and sunlight, little else in the garden can compete with their beauty or long season of bloom. Chinook sunrise rose, a new introduction for 2019, is earning rave reviews from many local gardeners who planted it in late spring. "It is fabulous, bush-like and a prolific bloomer," says Sharon Brokop, a St. Vital gardener. Exceptional disease-resistance and reliable winter hardiness will make chinook sunrise a popular choice.
Rosa Oscar Peterson is also a prolific and disease-resistant rose. This summer, however, an infestation of thrips wreaked havoc on some of my roses. Although Oscar’s foliage stayed healthy and glossy green, an insect routinely damaged the creamy white buds from the inside. I inspected each bud but couldn’t find the culprit and removed and destroyed the infected buds before they opened into distorted blooms.
In early spring, I usually spray my roses with a combination of lime sulphur insecticide-fungicide and horticultural oil (sold as a dormant spray kit) as a control measure for overwintering disease spores. Thrips overwinter in the soil and in plant debris. Ken Land, co-owner of St. Mary’s Nursery and Garden Centre, says that a serious pest infestation may also warrant a fall application of horticultural oil.
Pick a nice, sunny October day, Land says, when the temperature is above freezing but close to zero degrees. Apply early in the day, according to package directions, to allow the spray sufficient time to dry. Horticultural oil sprays are considered safe for use without harm to wildlife and non-target insects. Nevertheless, there is potential for beneficial insects overwintering on your rose to be smothered by the oil as well.
Land recommends disturbing the soil around plants by turning it over just before a hard frost or before the ground freezes to bring overwintering pests to the surface. "You can also apply a thin layer of diatomaceous earth to the soil surface around the base of plants or along flower beds," Land says. Diatomaceous earth is made from the fossilized remains of tiny, aquatic organisms and is a mechanical insecticide that may help to control thrips when they drop to the soil to pupate. Eco-Way Bug Killer Dust is the name of one product that contains diatomaceous earth for garden use. The label says it can be used without fear of harming pets, fish, birds and wildlife.
Land says that in order for diatomaceous earth to be effective, it must not be wet. Diatomaceous earth is only 60 to 70 per cent effective, Land says. As well, diatomaceous earth does not distinguish between pests and beneficial bugs. Always read the fine print before using any organic or chemical-based product in your garden.
Ninebark is one of the most significant shrubs for the residential landscape but can be subject to some bad press because of the belief that it has a propensity for powdery mildew. The truth is, you can pretty much guarantee powdery mildew when a plant is stressed by overcrowding and a lack of air circulation. The best practice is to give ninebark some breathing room and to avoid overhead watering. Land says that in October when all the leaves have turned colour, any leaves severely affected by powdery mildew will still be clinging to the shrub. "Strip the affected leaves from the plant and rake up and destroy the dead leaves on the ground," Land says. This will help to reduce the chance of reinfection next spring.
What about the lily? We mustn’t forget the lily, a species that is so perfectly suited to Prairie gardens. Unfortunately, the unholy mess made by the lily leaf beetle, which lays waste to stems, leaves and buds, has been a considerable deterrent to many gardeners. A promising means of biological control comes in the form of Tetrastichus setifer, a tiny parasitic wasp that lays eggs in the lily leaf beetle larvae.
As part of a research effort under the direction of Naomi Cappuccino, associate professor at Carleton University, Ian Wise, a local entomologist, has introduced T. setifer to test sites in Winnipeg and near Stonewall. The biocontrol program has been a success. "Areas where T. setifer has been introduced now have little to no beetle populations," Wise says.
The beetle continues to expand its range as indicated by its newly found presence in Manitoba. Nevertheless, beetle populations overall, Wise says, have declined. This may be due to a combination of factors, he says, such as fewer lilies being planted or warmer summer temperatures. The best course moving forward, Wise says, is to continue monitoring beetle distribution and abundance and to introduce T. setifer wherever localized high populations of beetles arise.
Earlier this summer, a contingent of lily enthusiasts from Manitoba attended the North American Lily Society’s 72nd annual symposium in Boston. Among them was Hugh Skinner, author and plant breeder. The mood at this year’s show was upbeat. "We are getting the message that we have a handle on the lily beetle problem and that with good management, there is no reason why we can’t grow lilies," says Skinner, who grows numerous lilies in his Manitoba garden. "There might be some minimal damage compared to the devastating damage that we’ve seen in recent years."
Skinner was excited to see centuria lily win best in show at the annual symposium. Centuria is a pastel yellow Asiatic lily developed at the Honeywood Heritage Nursery in Parkside, Sask. by Diann Putland, lily hybridizer. Putland, who died a few years ago, gave centuria bulbs to Skinner, who propagated them. Skinner sold centuria bulbs to a mail-order lily specialist in Maine who sold them to the person who exhibited centuria at the awards show and won. It’s a real Canadian story, Skinner says.
Plan to attend the MRLS fall bulb sale on September 21. This year’s event is being held at T and T Seeds and Garden Centre, 7724 Roblin Blvd.
It’s time now to start thinking about strategies for winter protection of newly installed perennials and the more delicate treasures in your garden. Take a cue from Sandra Venton, whose garden in St. James boasts an enviable display of David Austin roses. By late August or early September, she ceases deadheading the spent blooms. As rose hips develop, growth slows and roses start to prepare for winter dormancy. Once the ground is frozen, Venton prunes the stems back to about 30 centimetres in length and strips the remaining leaves from the branches.
Next, she mounds a layer of peat moss around the rose to protect the graft and adds enough oak leaves to completely cover the rose and peat moss. That’s not all. Venton also adds a framework of snow fencing, secured with rocks, to act as a wind barrier.
Back to school: Classes for the Master Gardener program begin Oct. 19. Visit mgmanitoba.com for full details.