Pest Management for Roses - The Organic Way
Roses are susceptible to aphids, spider mites, and thrips. Organic pesticides and other organic measures can be effective in ridding roses of these pests, including natural predators, and preventing them in the garden in the first place. Only with particularly heavy infestations should chemical pesticides, be used, as many of them kill beneficial insects, as well, and upset the natural balance in the garden.
Aphids are tiny insects that can be found in various colors, including green, pink, red or black. They cluster on new growth and cause it to be distorted or deformed. A strong blast of water will usually control them, but insecticidal soaps that kill the aphids, but don’t linger to cause damage to other insects later, are also effective. (Sunset, p. 530)
Spider mites are tiny, little spider relatives that come in red, Spider mites can become a problem in warm weather, when they defoliate and generally weaken plants. To detect them, hold a piece of white paper below yellow stippled leaves and gently tap the stem of the rose to knock them off onto the paper, where they will appear as tiny, moving specks. A fine webbing across leaves and around stems is also a sign of their presence. A sulfur spray can also be effective, but can be toxic to plants if used in conjunction horticultural oils used in insecticidal soaps. (Sunset, p. 555)
Thrips are almost microscopic. They dine on soft flower and leaf tissue and drink the plant juices, causing flowers and leaves to fail to open normally, and appear wisted, stuck together and discolored. Visible signs are stippled puckering in leaf and flower tissue and small, black fecal pellets on leaf undersides. Thrips appear as early as May and breed rapidly. They are particularly fond of white and light pink rose blossoms. Natural predators are the most effective organic method of controlling thrips. (Sunset, p. 579)
Aphids are repeat offenders from season to season, so practicing good garden clean-up, removing yard debris that eggs may be hidden in, can be an effective preventative measure. Also, eliminating ants is useful, because they feed on the sticky sap that aphids produce and often fight off natural predators. (Sunset, p. 530) Spider mites affect weak plants more, so growing strong, healthy plants can build resistance. (Sunset, p.555)
Planting repellant plants as rose companions can also be effective pest prevention. Aphids are repelled by coriander, chervil, nasturtiums, petunias, dill and rue. Spider mites are repelled by dill and coriander, and thrips are deterred by basil. (“Companion Planting”)
Many natural predators prey on spider mites, including lacewing larvae and five different kinds of predatory mites, which can be purchased at biological control companies. (Sunset, p. 555) Predatory mites occasionally dine on thrips, as well. Other natural predators of thrips are ladybugs and their larvae, green lacewing larvae and predatory thrips. (Sunset, p. 579) Natural predators are also attracted by certain plants, which can be planted as companions: borage, dill, and nasturtiums, and yarrow attracts ladybugs. (“Companion Planting)
References
“Companion Planting”. Golden Harvest Organics. September 27, 2009. http://www.ghorganics.com/page2.html
Sunset Books and Sunset Magazine, eds. “Sunset Western Garden Book”. Menlo Park: Sunset Publishing Corporation, 1998.
