P2472 Insect Pests of Roses

Insect Pests of Roses Damage Aphids cause damage by sucking plant sap. Because they often concentrate on tender growing tissue, like terminals and flower buds, they can cause distorted or stunted growth. These insects excrete a sticky substance called honeydew that con- tains large amounts of undigested sugars. We have tens of thousands of different Honeydew collects on leaves and supports species of insects and mites in Mississippi. a black fungal growth called sooty mold. Only a tiny percentage of these are pests of Sooty mold fungi are not pathogenic, but ornamental plants, and even fewer attack accumulations of sooty mold are unsightly roses. Still, there are some insects and mites and can interfere with photosynthesis. that cause serious problems for rose growers. Being able to identify these pests and Management distinguish them from non-pest species is Fortunately, there are many naturally the first step in control. occurring predators, parasites, and diseases This publication discusses the identifi- that help keep aphid populations in check. cation and biology of some of the most Avoid unnecessary insecticide use, which common rose insects. It also discusses non- can trigger aphid outbreaks by destroying insecticidal methods for helping keep pests these natural control agents. For heavy below damaging levels and lists insecti- accumulations of aphids on terminals or cides that can be used to control these pests buds, use a forceful spray of water to wash when outbreaks occur. There is also a sec- them from the plant physically. Avoid tion on insecticides and miticides that overuse of nitrogen fertilizer, as this discusses common active ingredients, lists encourages aphids. Some rose varieties are the pests they are most useful against, and especially susceptible to aphids, while oth- gives some of the most commonly avail- ers are more tolerant. Chrysler Imperial, able brand names. Midas, Tournament of Roses, and Pascali are examples of more susceptible varieties. Aphids (about one-eighth inch) Aphids are small, slow-moving, soft- bodied insects with piercing-sucking mouthparts. Several species occur on roses, but the rose aphid is one of the most common. Female aphids give birth to live aphid nymphs that can become mothers themselves within a week to 10 days. In addition, most aphids are females, and most female aphids are able to reproduce without mating. Consequently, aphids can quickly reach high populations. Aphids Control Thrips (about one-sixteenth inch) [acephate, acetamiprid, dinotefuran, imidacloprid, Thrips are some of the most malathion, insecticidal soap, pyrethrins + canola oil] important insect pests of Soil-applied systemic insecticides like dinotefuran roses. There are several or imidacloprid help prevent aphids. When foliar species, but flower thrips treatments are needed, products like insecticidal soap, and western flower thrips neem oil, or canola oil are least disruptive to biological are two of the most com- control. For heavy infestations that require immediate mon. Thrips are tiny, control, use foliar sprays containing acephate, elongate insects that are no acetamiprid, imidacloprid, or malathion. more than one-sixteenth of an inch long when fully Thrips Whiteflies (one-sixteenth to one-eighth inch) mature. Most adults have fringed wings that they carry folded lengthwise over Whiteflies are related to aphids. Adult whiteflies the body, but these are only visible through magnifica- are small moth-like insects that are covered with a tion. Immature thrips are usually light yellow to white, waxy powder. There are several different lemon colored and are spindle-shaped. species, but all carry their white, powdery wings folded tent-like over the body. They most often occur on the undersides of leaves, but clouds of adults will fly Damage around infested plants when disturbed. Immature In roses, thrips cause damage mainly by feeding whiteflies are immobile, scale-like insects that feed on on flowers. Their injury reduces the beauty of the the undersides of leaves. They are flattened and oval- blooms, and heavy infestations can prevent buds from shaped. Depending on the species, they may have opening. Thrips feed by punching plant cells with waxy filaments protruding from their bodies. These their needle-like mandibles and sucking up the result- traits are difficult to see without a hand lens. ing plant juices. This results in silvery or bleached damaged areas on flower petals that eventually turn Damage brown. Because feeding is often concentrated on young, actively growing tissue, petals and leaves are Like aphids, whiteflies suck plant sap through often crinkled or distorted as they continue to expand piercing-sucking mouthparts. They are also similar to after being damaged. Low levels of thrips injury tend aphids in their tendency to build to high populations to be more obvious on white or light-colored blooms and their ability to produce large amounts of honey- than on darker blooms, but severe injury will distort dew, which eventually results in sooty mold. blooms regardless of color. Management Management Avoid unnecessary insecticide treatments, which Thrips are carried by prevailing winds. Well- can disrupt natural biological control. placed windbreaks, either artificial or natural, can help protect rose plantings from the heavy populations of Control migrating thrips that often occur in late spring. These [acetamiprid, imidacloprid, dinotefuran, acephate, won’t intercept all of the wind-blown thrips but can insecticidal soap, neem oil, horticultural oil] help reduce heavy thrips pressure. Consider bloom Dinotefuran and imidacloprid are useful for con- color when choosing varieties. Dark-colored blooms trol of whiteflies when applied as soil drenches. When are less attractive to thrips than are white or light-col- attempting to control whiteflies with foliar sprays, be ored blooms. sure to apply at least two successive treatments 5 to 7 days apart. Control [acephate, acetamiprid, dinotefuran, malathion, imidacloprid, cyfluthrin, cyhalothrin, permethrin, spinosad, insecticidal soap] Soil drench treatments such as dinotefuran or imidacloprid will help control foliage-feeding thrips. Thrips feeding in flowers are more difficult to control. During late spring to early summer, large numbers of thrips migrate from maturing weeds and other hosts. Weekly sprays may be necessary to minimize damage during such periods of heavy migration. Thrips also Whitefly breed directly on roses, and these “local” populations 2 can require control throughout the year. Spinosad is Spider Mites (about one-thirty-second of an inch) one of the more effective foliar treatments, especially Although they are not for western flower thrips. insects, spider mites belong to a closely related group. Chilli Thrips Adult spider mites are so Chilli thrips, Scirtothrips dorsalis, is a nonnative small that they are barely thrips species that is not yet widely established in visible to the naked eye, but Mississippi. Rose growers need to be aware of this you can see them easily new invasive species. Chilli thrips attack a wide range through a 10X hand lens. Spider Mite of host plants, including roses, even the Knock Out Adults of most species are roses. Unlike most species of thrips that occur on somewhat globular in shape and have eight legs. roses, chilli thrips feed mainly on foliage, but they will There are many different species. Color may vary from feed in blooms. Heavy infestations can cause discol- red to green or yellow. One of the more common oration and distortion of rose leaves, resulting in species, the two-spotted spider mite, has a dark spot severe damage and even complete defoliation. These on either side of the body. symptoms are sometimes mistaken for herbicide or disease injury. If you notice these types of symptoms Damage in your roses, use a hand lens to check for thrips on Spider mites are some of the most common arthro- the undersides of leaves. Report suspected infestations pod pests of roses and some of the most difficult to of chilli thrips to your local county Extension office control. They feed by sucking the fluid from plant and/or the Mississippi Department of Agriculture. cells. Adults and nymphs cause similar injury. Feeding Spinosad, applied as a foliar spray, is one of the most by low numbers of mites is inconsequential, but these effective treatments for chilli thrips. It will take several pests have a very high reproductive potential and can treatments to obtain control. complete a generation in as little as 7 days. Heavy infestations can cause severe injury or even kill plants. Leafhoppers (one-eighth to one-half inch) Feeding by individual mites causes localized cell Leafhoppers are active, elongate, somewhat death, resulting in light-colored “stippling.” When wedge-shaped insects. They have piercing-sucking mite populations are heavy, these individual feeding mouthparts and readily run, hop, or fly when dis- sites merge, giving leaves a “bleached” or bronzed turbed. There are many different species. Most are appearance. Severely injured leaves may curl and drop green to yellow, but some species are brightly marked from the plant. At first, mite infestations are only on with yellow, red, or blue. the undersides of leaves. Under heavy infestations, the mites produce webbing and occur on the tops of Damage leaves and other plant parts. Both adults and nymphs suck sap from the undersides of leaves and tender stems, causing leaves to Management become spotted or turn yellow. A white or yellow stip- Populations of plant-feeding mites are often kept pling of the leaves is one of the most common in check by naturally occurring predatory mites and symptoms in roses. The stippling caused by leafhop- other predators. Outbreaks of spider mites often occur pers is usually larger and more widely spaced than following insecticide treatments targeted against other that caused by spider mites. In most cases, leafhoppers pests because these treatments destroy the predatory are minor pests that seldom cause serious injury. mites. Avoid unnecessary insecticide treatments.

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