Pest control of roses

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Growing Roses (p.10)

ANR-157, Reprinted October 1996. Recommended for Extension use by Dave Williams, Extension Horticulturist, Associate Professor, Horticulture, Auburn University. Former authors and revisers include Bridget Behe, former Extension Horticulturist; Patricia Cobb, Extension Entomologist; Austin Hagan, Extension Plant Pathologist; Kim Sheffer, former Horticulturist; Ron Shumack, Extension Horticulturist; George Stritikus, Extension Agent, and Dave Williams, Extension Horticulturist; all at Auburn University.

Rose Pest Control

Even though rose growing is a rewarding hobby, controlling pests is one of the requirements. Insects, mites, and diseases can quickly make a beautiful plant unsightly. The number and quality of blooms will also be greatly reduced if pest control is not practiced. The following sections give general information on common rose pest problems. For more information and for specific treatment recommendations, check with your county Extension agent.

Rose Insects

Aphids--In early spring aphids appear on the first buds, stems, and leaves. Occasionally they may become a pest during the summer but usually appear in heavier numbers again in the fall. Smaller or deformed blooms may result from aphids sucking the plant juices and stunting the plants. Heavy infestations of aphids result in the secretion of honeydew from their bodies. Honeydew makes leaves sticky and shiny and provides a starting place for sooty mold. Begin treatment when aphids build up on plants early in the spring. Inspect plants regularly. Treat in the fall to reduce the number of aphids that may produce overwintering eggs.

Caterpillars--Corn earworms, armyworms, rose slugs, and other caterpillars may feed on blossoms, buds, and leaves. Roses that are not treated with insecticides on a regular basis are more subject to damage by caterpillars than those on a regular spray program. Treat when small caterpillars are present. Removal of caterpillars is an alternative to chemical control.

Bud-, Blossom-, and Leaf-Feeding Beetles--These may attack roses in various stages of development.

Spider Mites--These pests attack the undersides of leaves. Infested leaves develop a yellow flecking or stippling, turn brown, curl, and drop off. In severe infestations webbing is present. Spider mites are extremely small and can be examined closely only by the use of a microscope or hand lens.

Some spider mites are green with two spots; others are red. Spider mites increase in number as the temperature increases, and they often reach the most damaging levels during mid-summer. Excessive use of carbaryl (Sevin) destroys spider mite enemies, and mites become more numerous. To control spider mites keep the rose bed and surrounding areas free of weeds. Direct spray to the undersides of leaves.

Thrips--Thrips are tiny yellow or straw-colored insects that injure rose petals. Thrips rasp slits in petals and cause blooms to become brown-flecked in appearance. Blooms damaged by thrips often fail to open properly. Shake an infested flower over a sheet of paper or pull back petals of blooms to see these tiny insects. Be sure to destroy all old blossoms.

Nematodes--Several nematodes are common parasites on roots of roses. Symptoms of nematode injury vary with plant type and age, kind of nematode, and degree of infestation. They include lack of vigor, premature leaf fall, yellow foliage, stunting, and twig and branch die-back. Roots infected by the root-knot nematode (Meloidogyne sp.) have obvious galls (usually less than 1/4 inch in diameter). Other nematodes that may damage roses include lesion, spiral, and stunt nematodes. Roots attacked by these nematodes are usually rough, discolored, decayed, and without galls. Nematode damage is often mistaken for lack of fertilizer or poor soil conditions. Aboveground symptoms are similar to those caused by crown gall.

When purchasing roses, inspect roots for nematode damage. No matter how careful you are in carrying out all other precautions, your efforts are largely wasted if nematodes are brought into the home garden on infested plants. Avoid the movement of soil from known nematode-infested areas in your yard to uninfested areas.

Contact your county Extension office for information on nematode control. Additional information on nematodes on roses and their control can be found in ANR-689, "Nematode Pests of Flowers and Woody Plants."

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