Managing Insects and Related Pests of Roses Bastiaan M
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B-6068 6-99 Managing insects and related pests of roses Bastiaan M. Drees, Brent Pemberton and Charles L. Cole* to outbreaks of spider mites. Thus, protecting exas is well known for roses. In the Tyler roses from insects and mites requires continual region, roses are grown commercially in care and substantial knowledge of pests and greenhouses and outdoor nurseries, where management alternatives, including pesticides Tfield-grown cut flowers, potted miniature roses, and their use. bare-root roses for use in landscapes, and potted roses for the garden-center trade are produced. Monitoring and identifying Although several species of roses are native to the state, the rose industry is based primarily on pests and their damage the many exotic rose hybrids available, including Detecting and identifying pests are the first antique and shrub roses, which have fewer pest steps in managing insects attacking roses. Inspect problems. One of the largest antique-rose pro- plants regularly for pests and the injury they ducers in the nation is produce. For example, located near Brenham, check the underside of a Texas. set number of leaves weekly for such pests as Because roses are grown spider mites or aphids. and appreciated primarily Regular inspections can for their aesthetic value, help growers detect the the plants—and particularly arrival of new pests or the blossoms—should be document the abundance relatively free from pest of pests over time. In addi- damage. Rose plants in the tion, monitoring helps landscape need not neces- growers time their sup- sarily be blemish-free, but pression methods and still should be healthy and evaluate their effectiveness add to the plantings’ overall better. In greenhouses, yel- beauty. low sticky cards can be Many species of insects Figure 1. Rose injury caused by thrips. hung over the plant and mites attack and injure canopy and inspected reg- roses. Under certain condi- ularly to indirectly monitor adult populations of tions, roses become particularly susceptible to many insect pests of roses, such as winged certain pests. For example, greenhouse-grown aphids, thrips and whiteflies. roses are more susceptible than field-grown roses Correct identification enables growers to choose the best methods to control pests while *Professor and Extension Entomologist; Associate Professor; helping preserve beneficial insects. Not all Emeritus Professor and Extension Entomologist; The Texas A&M insects that frequent roses are damaging. Many University System. are incidental; some are pollinators; and others are beneficial natural enemies that feed on harm- ful species. Insects that attack roses can be divid- ed into two groups according to the way they feed on plants and the damage they cause: ■ Sucking insects, which insert their mouth- parts into plant tissue and suck out the juices, sometimes transmitting diseases to roses in the process; and ■ Chewing insects, which chew on plant tis- sue and may damage all or parts of the plant, including roots, stems, leaves, buds and open flowers. Although spider mites are not insects, the symptoms they produce (stippling, bronzing of Figure 2. Aphids on a rose. leaves) are similar to those of sucking insects. Like spider mites, thrips rupture plant cells and that mature in 7 to 8 days. Because aphids breed suck out the cell contents. Thrips also often continuously, populations grow quickly, especial- injure expanding flower petals, producing discol- ly in cool weather. ored, malformed blooms. Aphids usually live together on buds, the Sucking pests, such as aphids, leafhoppers, underside of leaves or in the plants’ growing tips. scale insects and whiteflies, produce these symp- They suck out plant sap and excrete a sweet, toms: sticky substance called “honeydew” that collects on leaves and stems. A black fungus called sooty ■ Discoloration (yellow or brown) and necrot- mold grows on honeydew, making it look ugly ic (dead) spots on leaves or petals; and reducing photosynthesis. Plants heavily ■ Wilted appearance of plant or plant parts; infested with aphids appear wilted. Some aphid ■ Curled, malformed leaves and petals; and species cause leaves to yellow or drop from the plant; other species stunt and curl young leaves. ■ Shiny, sticky “honeydew” or black-colored Heavily infested buds may fail to open, be coating of sooty mold. deformed or produce small blossoms (also see Chewing pests, such as caterpillars, beetles, Extension publication B-6047, Aphids in Texas grasshoppers and leaf-cutter bees, produce these Landscapes). symptoms: Leafhoppers: Leafhopper species are about ■ Holes in foliage or stems; four times longer than wide. When full grown, ■ Discolored areas on the surface or margins they range from 1/4 to 1/2 inch long. Adults vary of leaves or petals; in color from gray to yellow and green; some species have patterned markings. The immature ■ Severed stems, leaves or buds or wilting of forms (nymphs) resemble adults but are lighter stem or cane (limb girdling); in color and lack wings. Both adults and nymphs ■ Wilting of plant (root damage by white can injure roses. Some species feed on tender grubs or other root feeders); and stems and leaf petioles; others, such as rose ■ Semicircular holes in leaf margins (leaf-cut- leafhoppers, feed on the underside of leaves, ting bees). causing whitish stippling. In Texas, leafhoppers attack roses from early spring until late fall. Scale insects: Several scale insects occasional- Common insect and mite ly attack roses, but the most damaging is rose pests of roses scale. Small and soft-bodied, scale insects secrete a material that forms a shell or “scale” over the Aphids: Many species of aphids or plant lice, insect itself. Female rose scales are round and including the rose aphid, attack roses. Aphids are dirty white. Males are elongate and snow white. small, soft-bodied winged or wingless insects 1 1 When mature, these insects insert their mouth- about /25 to /8 inch long with relatively long parts into the plant tissue and remain there, pro- legs and antennae. Species vary in color from tected under their scale covering, for their entire black, green, yellow to even pinkish. Some life span. Females deposit eggs beneath the old aphids lay eggs; others give birth to live young scale covering. When the eggs hatch, the young, six-legged Migrating adult popula- scale insect “crawlers” disperse throughout the tions, particularly in late new tissue and attach themselves to the plant. spring, damage roses most. Heavily infested canes may become encrusted in Thrips feed predominately the scales. Scales become most abundant under on pollen, but also attack high humidity and reduced sunlight. They not tender plant tissue, rasping only spoil the plant’s appearance, but also great- the surface tissue from ly reduce plant vigor (also see Extension publica- leaves, buds and petals. tion L-1827, Scale Insects on Ornamental Plants). Recently injured tissue Whiteflies: Adult whiteflies are small, white, looks silvery. Heavy infes- soft-bodied insects. Weak fliers, they resemble tations result in discolored, tiny snowflakes fluttering about a plant. Figure 4. A thrips. deformed growth and Immature whiteflies attach to the underside of blemished, deformed leaves and resemble scale insects. Both imma- flower petals. ture and adult forms feed on roses, leaving yel- Leaf-feeding beetles: Several species occa- low spots on the leaves. Heavy infestations can sionally feed on rose plants, chewing plant tissue cause defoliation. Much like aphids, whiteflies from leaves, buds and petals. Rose chafers and secrete honeydew, causing plants to be covered June beetles are brown; rose leaf beetles are with a black sooty mold (also see Extension pub- small and metallic green; and twelve-spotted lication L-1299, Whiteflies). cucumber beetles are 3/8 inch long and greenish- Spider mites: Although several species of spi- yellow with black spots. der mites attack roses, the most common is the Caterpillars: Many species of caterpillars, the two-spotted spider mite. Mites are tiny, scarcely immature stages of moths, can be incidental visible without magni- pests of roses. Although most feed on leaves fication. Their color voraciously, only a few damage or defoliate varies in shades of yel- plants extensively. Leafrollers are small, pale- low, red and green green black-headed caterpillars that produce leaf marked with two mines when small and later feed inside leaves darker spots on their they have rolled up and tied with silk. Leaf tiers backs. All develop- also draw several leaves or parts of leaves mental stages of spider together with silk. mites usually live on Figure 3. A spider mite. Grasshoppers: Several species of grasshop- the underside of the pers feed on rose leaves, buds, flowers and leaves, but may be found elsewhere on heavily stems. Winged adult grasshoppers are difficult to infested plants, which they may cover with a control in the times of year they migrate to rose fine web. Female mites lay clear, spherical eggs plantings from surrounding vegetation where on the underside of leaves. Eggs develop into they developed. adults in 5 to 20 days, so populations grow quickly, especially in hot, dry weather. Leaf-cutter bees: These solitary bees nest in burrows and hollowed twigs and stems. Adult Spider mites rupture plant cells with their females cut circular to elongate pieces of leaves mouthparts and suck the juices, producing feed- from roses to build walls and partitions of nest- ing punctures that look like tiny light-colored ing cells where their young develop. Cells are spots, giving leaves a stippled appearance. provided with nectar and pollen collected from Leaves of heavily infested plants turn yellow, flowers as food for the larvae. then brown and eventually fall from the plant (also see Extension publication L-1244, Indirect pests of roses: Many insects in and Destructive Mites in the Home Garden). around rose plantings should be controlled when they become numerous enough to be a nuisance.