Fungus Diseases

Problem/Symptom	Cause	Solution
Circular black spots 1/4 inch in diameter appear on upper leaf surfaces. Each black spot is surrounded by a yellow halo. As the spots enlarge and coalesce, the entire leaf turns yellow and falls from the plant.	Black Spot. This fungus disease is most common in humid and rainy conditions; the fungus spores germinate in water. Once a plant is infected, the fungus will remain in the canes through the winter and reappear on the next season's growth. VERY common in the Pacific Northwest.	There is no chemical cure for infected plants. In the early spring, after an infection, prune the canes back lower than normal to eliminate fungus spores that remain on the canes over winter, and apply a commercial anti-fungal spray before the leaves open. To prevent black spot from infecting new plants, spray with a synthetic chemical fungicide once every 10 days, starting in midspring. If symptoms appear, remove and destroy all infected leaves, including those on the ground. Do not water plants from above; wet leaves are hospitable to germinating spores.
Leaves, especially new leaves, become twisted or curled and are covered with a white powder. Flower buds and canes may also be affected.	Powdery mildew, a fungus disease carried by wind. The problem is most severe when nights are cool and humid, and days are warm and dry.	Remove and destroy all infected leaves, including those on the ground. To prevent mildew or to arrest its spread, apply a fungicide once every 10 days, starting in midspring.
Small red, brown or purple spots develop on upper leaf surfaces. The center of each spot eventually dries out, turns white and may fall out of the leaf. Leaves eventually turn yellow and fall from the plant.	Spot anthracnose, a fungus disease. The fungus spreads in water.	When symptoms appear, begin spraying with a fungicide once every seven days until all signs of the disease are eliminated. Do not water plants from above, since the fungus spreads in splashing water.
Rosebuds fail to open and are covered with a grayish brown, fuzzy mold. Open flowers are flecked with yellow or brown and lower petals are wilted and brown. The stems below infected flowers become discolored.	Botrytis blight, also called gray mold, a fungus disease that spreads in moist air and cool temperatures.	There are no chemical cures for blight once it occurs. If symptoms appear, cut off and destroy all infected plant parts. Spray with a fungicide to keep the disease from spreading.
Red or brown sunken spots with dark margins develop on canes. Cracks may appear within the spots. The spots enlarge and eventually encircle the cane. Leaves and stems above the damaged area turn yellow, wilt and die.	Canker, a fungus disease. The fungus spreads in water and enters the plant through cuts or wounds in the canes. The problem is most severe in early to middle spring, when plants come out of dormancy.	There is no chemical preventive or cure for canker. When symptoms appear, prune infected canes below the canker. Use sharp pruning shears and make the cut just above a node at a 45 degree angle.
An orange, powdery substance appears on the undersides of the leaves. Eventually, yellow or brown spots appear on upper leaf surfaces. Infected leaves may wilt or curl.	Rust, a fungus disease that spreads in moist air and moderate temperatures. The problem is most severe in the Pacific Northwest, where the climate is cool and humid.	Remove and destroy all infected leaves, including those on the ground. Avoid overhead watering because the fungus spreads in water. To prevent the disease, spray with a fungicide every 7 to 10 days in cool, wet weather.

Unwelcome Guests

 

Problem/Symptom	Cause	Solution
Leaves curl, rosebuds and foliage wither or become distorted in shape. A clear, sticky substance that attracts ants appears on foliage.	Aphids, semitransparent insects 1/8 inch long that cluster on new growth and flower buds. They suck the juice from the plant and secrete the sticky substance. Aphids can carry and spread diseases.	Aphids may be knocked off plants with a stream of water. In severe infestations, spray with an insecticide or an insecticidal soap.
Small, rounded holes appear in leaves. Eventually, the entire leaf surface between the veins disappears.	Rose slugs, the larvae of sawfly wasps. The slug is light green with a dark brown head and up to 1/2 inch long. Some species have shiny bodies; others are covered with hair. Rose slugs generally feed on the undersides of leaves; they do not eat buds and flowers.	Spray with an insecticidd and make sure the insecticide covers the undersides of leaves.
Buds do not open, or flowers are deformed. Petals have brownish yellow streaks and small dark spots or bumps. White and pastel roses are particularly susceptible.	Thrips, tiny orange insects with elongated bodies. Thrips feed at the bases of rosebuds and on the petals of open flowers. They seem to be attracted to light-colored blossoms.	To discourage thrips from attacking, spray plants with a systemic insecticide just before the buds open. If signs of thrip damage appear, remove and destroy infected flowers and buds. Spray infected plants with an insecticide. If the infestation is severe, repeat applications may be necessary.
Roses fail to blossom or existing buds suddenly turn black and die. The foliage and the stem surrounding affected buds may also blacken and die.	Rose midge, a fly larva that is white and 1/12 inch long. The larvae feed in clusters at the bases of rosebuds.	Prune off and destroy all infested plant parts. Spray plants with an secticide and apply a systemic insecticide to the ground around the plants where the larvae pupate.
Holes appear in flowers and then in leaves. Light-colored flowers are especially susceptible.	Japanese beetles, shiny copper-and-green, hard-shelled insects up to 1/2 inch long. Beetles move from flower to flower, consuming the petals before they eat the leaves. They seem to be attracted to light-colored blooms.	Pick beetles off plants by hand and destroy them. Spray the plants with an insecticide. In late summer and in spring, treat the ground around affected roses with a grub-controlling insecticide or with milky spore. In the fall, rake up fallen leaves; adult beetles spend the winter in plant debris.
Leaves become dry and have a full bronze sheen. Tiny specks may be visible on the undersides of the leaves. Eventually, thin webbing appears on the foliage.	Spider mites, nearly microscopic pests that may be red, black, yellow or green. To confirm their presence, shake a leaf over a piece of white paper; the mites will be visible moving against the white background. Mites proliferate in hot, dry weather.	Knock adults off plants with a strong stream of water. Spray with a miticide three times, three days apart. Use different miticides; mites may build up resistance to a single miticide. Mites produce new generations in a few days, so repeat treatments will be necessary.
Small circles or ovals appear in leaf margins.	Leafcutter bees, which are shiny black, blue or purple bees. The bees do not eat the foliage; they use leaf material to build their nests.	Prune out canes that have damaged foliage. Since leafcutter bees are pollinators of several crops, the use of chemicals to destroy the bees is not recommended.
Round or oval masses appear on stems and canes. Foliage wilts, turns yellow and drops from the plant. Growth is stunted and flowers are not produced.	Rose scales, 1/8-inch, white, gray or brown insects with crusty shells. Scales usually appear in clusters.	Prune out and destroy heavily infested canes. Spray plants with an insecticide. To prevent scale infestation, spray plants with horticultural oil in early spring.
Holes appear in unopened rosebuds. Leaves and stems may also have holes or may be chewed off.	Caterpillars, the larvae of moths and butterflies. Most are yellow or green and up to 1 inch long. Some, such as budworms, attack only the flowers; others eat the leaves and stems.	Spray with Bacillus thuringiensis, called Bt, a bacterium fatal to caterpillars but harmless to plants and other animals. If caterpillars return to your garden every spring, Bt can be sprayed in anticipation of the problem.
Upper surfaces of leaves are covered with small yellow specks. Leaves may curl.	Leafhoppers, which are triangular, white or light yellow insects 1/8 to 5/8 inch long. They feed on the undersides of leaves and suck the sap from the foliage. Leafhoppers can carry and spread diseases.	Spray with an insecticide or insecticidal soap. In the fall, rake up leaves and remove weeds that can harbor leafhopper eggs through the winter.
Growing tips, foliage and canes wilt. Swollen areas up to 1 inch long appear on canes.	Borers, moth larvae that are white or yellow worms up to 1 inch long. Borers enter the canes through wounds and through pruned stem tips.	Cut off the affected area. Make the cut below the swelling on the cane to be sure you remove the borer. To prevent borers from entering canes, apply shellac or white glue to the exposed tips after pruning.
Overnight roses are chewed and trampled.  Buds and blooms are damaged the most.	Deer	See "Deer Control Methods" Word Doc for help.

Other Problems

Problem/Symptom	Cause	Solution
Round growths about 2 inches in diameter appear at the base of the plant. The growths are light green when young and turn brown and woody as they age. Plant growth is stunted, foliage is abnormally small and few buds are produced.	Crown gall, a disease caused by bacteria that live in the soil. The bacteria enter a plant through the roots or through wounds at the root area. The bacteria cause abnormal cell growth, which produces the galls.	There are no chemical controls for crown gall. Small galls may be pruned out with a sharp knife or pruning shears. Disinfect tools with alcohol or household bleach after each cut. In severe cases, remove the plant and the soil surrounding the roots to prevent the bacteria from spreading.
Leaves or mottled or streaked with yellow or the develop a pattern of yellow netting. Plant growth slows.	Mosaic, a virus disease that is often transmitted by aphics and other insects. Although the virus does not affect flowers, it detracts from the overall appearance of the plant.	There are no chemical controls or cures. In mild cases, symptoms often disappear by themselves. In severe cases, infected plants should be removed to prevent the virus from spreading.