Perfect roses are prized for gardens, bouquets and flower shows, but roses attract pests that blemish leaves and flowers.
A number of lethal insecticides are available to eliminate pests, but Environment Canada urges gardeners to rethink their use. Not all insects are pests; many are their predators. A garden wiped clean of insects by pesticides is vulnerable to infestation.
Grow healthy roses with a variety of insects. Soapy water eliminates aphids without harming other insects.
Learn to identify the insects on your rose bushes so you can target the pests. A variety of ladybug beetles have varying colors and spots, but all are beneficial in that they eat aphids, one of the more prevalent pests that attack roses. They also eat whiteflies that chew holes in foliage. Bees pollinate flowers. Praying mantises, wasps, dragonflies and damselflies prey on rose pests, as do spiders, lacewings and ground, blister and rove beetles. All these beneficial insects are killed by broad spectrum pesticides.
Aphids love roses. They appear in hot weather on rose bushes that lack nutrients or that are weakened after the first flower display. They are tiny and cluster on new growth, especially tender young flower buds. Green, white, red, brown or yellow, they can increase quickly and mass in the hundreds or thousands on tender new growth to suck out the vital juices. They produce a sap called honeydew that attracts ants and other pests, and it can develop a black sooty mold that turns rose foliage a dirty gray.
Aphids are easily contained by nonchemical methods. Rose growers should inspect their plants regularly. At the first sign of aphids, cut away all severely infested leaves, flowers and branches. Do not compost these--remove them and burn them to get rid of the aphids.
Mix a few drops of dishwasher or insecticidal soap in a bowl with warm water and wet the rose foliage and flowers. Coat the leaves and buds with suds. You may also load a spray bottle with soapy water and spray it on. Be careful to wet all sides of foliage and flowers. Do not wash off. Repeat this every other day for two weeks to kill the active aphids and the eggs and larvae. Reapply after a rain.
In the case of a severe infestation, use a strong spray from your garden hose to blast the aphids off the foliage. Follow up with a bath in soapy water. Thoroughly coat the leaves, flowers, buds and woody parts of the rose to be sure to eliminate eggs and larvae.
After two weeks, carefully watch the rose plant for any reinfestation. Some rosarians spray their roses daily with cold water as a preventative.
Companion planting is also effective. Roses love (and aphids hate) garlic, mint, coriander, anise, petunias and nasturtiums. Planted in your rose beds, they will guard against disease and pests.