Beware Of This “Sucker”
Roses grown in landscapes are susceptible to attack from a variety of aphid species; however, the predominant aphid that feeds on roses cultivated outdoors is the rose aphid, Macrosiphum rosae. The rose aphid has a wide distribution, feeding on roses throughout the U.S. Rose aphids are soft-bodied, pear-shaped insects, approximately ¼-inch or 0.63 cm in length. They can vary in color from green to pink to red. Rose aphids have two tubes (called cornicles) that protrude out from the end of abdomen, which is where alarm pheromones are emitted. Rose aphids overwinter as eggs on rose canes.
Rose aphids generally initiate feeding on roses in early spring as the new flush of growth emerges. They feed on plant fluids within the phloem sieve tubes (food-conducting tissues) with their piercing-sucking mouthparts. Like other aphid species, rose aphids tend to congregate or cluster in large numbers feeding on the terminal growth including leaves and stems, and developing flower buds, and on leaf undersides. Their feeding causes leaves to curl downward and deforms flower buds, which may result in flower buds aborting or falling off prematurely before opening. In addition, aphids secrete honeydew, which is a clear sticky liquid emitted during feeding. Honeydew attracts ants, wasps, hornets and serves as a growing medium for certain black sooty mold fungi. Rose aphids don’t usually cause direct harm to roses unless they are present in excessive numbers, in which case, they may kill buds or reduce flower size. Similar to other aphid species, rose aphids have a very high reproductive capacity, which enables populations to increase dramatically during the season. Furthermore, if rose aphid populations reach high levels and the quality of infested rose plants declines (as a food source), winged forms of adults will develop allowing them to move from plant-to-plant.
Rose aphids are susceptible to an array of natural enemies including parasitic wasps or parasitoids in the genus Aphidius and predators such as ladybird beetles, green lacewings and syrphid or hover flies. These may provide natural regulation depending on the number of rose aphids present. However, it is also important to control ants because they feed on the honeydew produced by rose aphids, and protect the aphids from natural enemies. If ants are present, then this may result in insufficient regulation by natural enemies. A forceful spray of water, applied routinely (twice per week), will quickly remove aphids (and mites) from rose plants without causing long-term harm to natural enemies. This technique is effective in controlling or regulating rose aphid populations contingent on not promoting diseases such as blackspot (Diplocarpon rosae) or rust. Contact or systemic insecticides may be effective in preventing or regulating rose aphid populations if used properly. For example, multiple applications and thorough coverage of all plant parts — especially the new growth — will be required in order to effectively regulate populations of rose aphids with contact insecticides. There are many products commercially available for control or regulation of rose aphid populations including ‘selective’ insecticides: insecticidal soap (potassium salts of fatty acids), horticultural oils (petroleum and/or neem-based) and pyrethrins. It is important to note that many contact insecticides may be directly harmful to natural enemies (beneficial insects) so these materials should be used judiciously in order to prevent outbreaks of rose aphids. Systemic insecticides applied to the soil/growing medium must be used early to ensure that the active ingredient is present in the new growth just as rose aphids start feeding. There are a number of products commercially available with the following active ingredients: imidacloprid, dinotefuran, thiamethoxam, clothianidin, acephate and disulfoton. Be sure to thoroughly read the label of all insecticides prior to making an application.
HAPPY ROSE GROWING
Raymond A. Cloyd
Professor and Extension Specialist in Horticultural Entomology/Integrated Pest Management
Kansas State University
Department of Entomology
123 Waters Hall
Manhattan, KS 66503-4004
Phone: (785) 532-4750
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