WSU CAHNRS and WSU Extension


Search plant problems by plant name

? Help on search

A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  R  S  T  V  W  Y 

Plant NameTypeDescription 
Black moldRoseDiseaseBlack mold primarily affects material used for propagation. The fungus grows on cut surfaces, such as at the contact points between rootstocks and scions and rootstocks and bud shields. This causes graft failures. A gray-white fungus growth is the first symptom of infection. This growth soon turns black as spores are produced. Certain rose varieties are extremely susceptible, such as R. chinensis var. manetti, while others rose varieties are resistant or immune.
Black spotRoseDiseaseBlack spot is a very common fungal infection of the leaves and canes of roses. Round black leaf spots (sometimes with fringed or feathery edges) may be accompanied by leaf yellowing and leaf drop in susceptible varieties. Canes often display small reddish-purple to black spots. High humidity, rain, and overhead watering contribute to the development of this disease. Black spot is spread by splashing water.
Botrytis bud and twig blightRoseDiseaseBotrytis can infect stems and flowers, including stubs left from pruning or flower removal. Infected tissues are usually covered with a fuzzy, gray-brown growth. Infected flower buds may not open, and can show sunken, smooth, grayish spots on the bud and flower stem. Sunken, dead areas may develop on the canes. Infection is worst during cool, wet weather.
Brand cankerRoseDiseaseBrand canker is a fungal disease that often infects plants in the winter, especially when winter protection of roses keeps the canes moist. Initial symptoms of infection are small dark red spots on the canes. These get larger and develop distinct dark red or purplish margins. Later the spots turn light brown in the center. Insect wounds and pruning wounds are common sites of infection. Brand canker may resemble common canker.
Bullheading (cold damage)RoseDiseaseBullheads are the most prevalent when temperatures dip to 53-59 degrees Fahrenheit during early flower development. Low temperatures appear to alter metabolic activity, which results in the abnormal appearance of buds and resulting flowers. Flower buds exhibit a flat-topped appearance and weigh more than normal buds with a pointed tip. The number of short petals and petaloids increases, as well as the amount of secondary florets near the bases of flowers. Baccara, Talisman, and cultivars belonging to the Columbia family are especially susceptible.
Common cankerRoseDiseaseCommon canker is a fungal disease that infects plants through long stubs left by improper pruning or through other wound sites. Small yellow or reddish spots appear on canes and gradually enlarge. Later, the centers of the spots turn light brown and develop lengthwise slits in the bark. Common cankers have dark brown edges and often occur at the cut ends of canes. Common canker may resemble brand canker.
Crown gallRoseDiseaseCrown gall on roses usually occurs at or just beneath the soil surface. It may also be found on stems and roots. Young galls appear as a soft thickening in stems or roots and are green to white in color. Older galls are woody, dark and corky-looking on the outside, and light-colored on the inside. The bacterium that causes crown gall is present in the soil and infects through wounds on the roots or stem. It can be spread from infected soil by water movement. Damage to plants varies with location and size of galls.
Downy mildewRoseDiseaseDowny mildew can affect leaves, stems, flower stems, and flower parts. The infection is usually found only on young growth. On leaves, symptoms include purplish or brown spots, usually between veins, and yellow leaves with green spots. Infected leaves may drop off the plant. Grayish fungal masses may be found on the underside of some infected leaves (unlike powdery mildew, which is white and found on both sides of leaves). Symptoms on stems and flower parts can include small or large purple to black spots. Small infected twigs can be killed.
Powdery mildewRoseDiseasePowdery mildew is a fungus attacking leaves, stems, and flower parts. Usually young growth is most severely affected. Reddish, blister-like areas on the upper side of leaves are followed by powdery white growth, which can appear on either side of the leaf. Infected young leaves are often distorted. Flowers and stems also display the white growth. Some varieties of roses may drop infected leaves, while others are more resistant to powdery mildew. The disease is most active during cool, dry, cloudy weather.
RustRoseDiseaseRust usually is first noticed as clumps or pustules of red to orange powder on the lower surfaces of leaves. The upper surface may also show yellow, orange, or brown spots, corresponding to the location of the pustules on the underside. Symptoms may also appear on young stems and green flower parts. Some rose varieties are tolerant of infection, while others drop infected leaves. This fungal disease can be spread by wind or splashing water and is most serious during cool, humid weather.
VirusesRoseDiseaseThe most common virus disease of roses is rose mosaic, which may cause leaves to show yellow lines, rings, mottles, or netted patterns. These symptoms usually are seen in the spring on part or all of the plant and may not be present at other times. Some infected plants show no symptoms. Rose mosaic viruses are not spread by insects or pruning tools, but can be transmitted between plants by grafting or budding. Infected plants may be less vigorous and more sensitive to winter injury. The agent which causes rose spring dwarf is also probably a virus. Symptoms of this disease are mainly seen on new growth in the spring. Emerging leaves are short, curved, and clustered in a ball or clump on very short shoots. The new leaves are also distinguished by a yellow net-like pattern along the leaf veins. This chlorosis may also be seen on new leaves in the fall. Branches sometimes grow in a zigzag pattern. Infected plants appear to be less vigorous than healthy plants.
Leafcutting beesRoseInsectLeafcutting bees remove smooth circular or semi-circular notches from the edges of leaves of roses and other plants. The leaf pieces are used by the bees to create protective cells for raising their young. Leafcutting bees are important pollinators and seldom do major harm to plants.
LeafrollersRoseInsectSeveral different caterpillars roll leaves on roses. Among these are the obliquebanded leafroller, which is green with a dark head, and the orange tortrix, which is tan to greenish with a tan head. Leafrollers are often found near the tips of shoots. They feed inside the rolled leaves, which are held in place with webbing.
Redhumped caterpillarRoseInsectThe redhumped caterpillar is the larvae of a 1" gray-brown moth. The mature larvae are yellow with a red head and hump, and have orange, black, and white lengthwise stripes. The body of the caterpillar also has dark "spikes" on it. Young redhumped caterpillars are found in clustered colonies which disperse as caterpillars mature. They eat entire leaves (except the major veins).
Root weevilsRoseInsectSeveral species of weevils feed on roses. Adult weevils feed on the leaves, leaving small ragged notches along the edges. They may also feed on the flowers. They are wingless gray, brownish, or black beetles that feed at night. The larvae live in the soil and feed on the roots.
Rose aphidsRoseInsectRose aphids are small, soft, pinkish or green insects found on the succulent new growth, including buds and stems. White cast skins can also be present. Heavy aphid feeding can reduce the quantity and quality of the flowers produced.
Rose gallsRoseInsectInsects can cause two types of rose galls: spiny rose gall and mossy rose gall. The spiny rose gall is caused by tiny cynipid wasps. They produce small hard internal caverns armed with stout, sharp spines on the exterior. The galls usually occur on the surface of leaves, but they sometimes occur on stems. These rose galls do not appear to harm the plant. Spiny rose gall develops exclusively on wild roses. Some people consider them to be rather attractive nuances. The mossy rose gall is also caused by cynipid wasps. This gall resembles a highly filamentous and spongy twig gall that can exceed the size of a golf ball. It contains numerous caverns with resident wasp larvae. It also appears harmless to the plant, and occurs on domestic roses only.
Rose leafhopperRoseInsectRose leafhoppers are small, active, whitish-green insects which hop when disturbed. The nymphs (immature) are white with red eyes. Rose leafhoppers feed on the leaves, causing white or pale blotches that resemble, but are larger than, spider mite stippling. Cast skins can be found on the underside of leaves. The adults lay eggs in the bark, causing small dark spots on the canes. The emerging nymphs cause wounds to the bark which may provide a site for fungal infections. Leafhoppers are rarely a serious concern.
Rose midgeRoseInsectThe rose midge is a tiny yellow-brown or reddish fly that lays its eggs in newly developing bud and shoot tips. The hatching maggots feed on the growing tips. New buds and shoots are deformed and killed and the dead tissues turn brown or black. Abnormal flower development from damaged buds may also be seen.
RoseslugRoseInsectRose slugs are small yellow-green larvae (about 1/4" long) that skeletonize the upper leaf surface. Signs of feeding include dry brown blotches, where all of the leaf except the veins and the lowest layer of leaf tissue are removed. Rose slugs are not true slugs, but are actually the larvae of a sawfly. They rarely occur in large numbers but can do considerable aesthetic damage.
Spider mitesRoseInsectSpider mites are tiny, eight-legged, and yellowish to brown in color. They cause mild to severe stippling (little specks or dots) on leaves. Usually yellowish to bronze in color, stippling can, in severe cases, cause leaves to drop. Fine webbing is often present, especially on the underside of leaves. Mites may be found on either leaf surface, but normally on the underside of leaves.
ThripsRoseInsectThrips are tiny yellowish to dark insects that feed in flower and leaf buds. Damaged leaves may be distorted, while infested flower buds may be distorted if they open. Heavily infested flower buds may fail to open. Infested flowers have brown spots on the petals. Thrips on roses are mainly an aesthetic concern.
Tobacco budwormRoseInsectTobacco budworm larvae attack several ornamental flowers including petunia, rose, geranium, and nicotiana. They feed primarily on buds, petals, and developing seed pods, but will feed on shoot tips and foliage if flower buds are not available. On most hosts, larvae prefer to tunnel into buds, but they will also feed on the petals of opened flowers (especially on petunia). Damaged buds fail to open, resulting in loss of color in floral plantings. If buds open, flowers and leaves appear ragged or tattered. The adult is a greenish-brown moth with cream-colored bands on the wings. It is about 3/4 inch long with a wingspan of about 1 1/2 inches. Eggs are laid on blossoms, fruit, or shoot tips of plants. Very young larvae are yellowish or light yellow-green, but the color of older larvae is variable. Mature larvae may be light to dark green, brown, tan, or reddish. These older larvae usually have stripes along the sides and a brown head. Mature larvae drop to the ground and pupate in the soil around host plants. There are typically two or more generations per year. Tobacco budworm overwinters as pupae in the soil.
Western spotted cucumber beetleRoseInsectThe western spotted cucumber beetle is a pest of many ornamentals and vegetables. About 1/4" long, the adult beetles have yellow wing covers with black spots. The rest of the body is black. Adults feed on leaves of plants, while the larvae feed on the roots of some plants.