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Symptoms, Causes, and Cures
Scan this list of common flower diseases and pests for those symptoms that match damage, insects or other problems you see in your flower garden. Click on each problem’s tab to find symptoms, causes, and cures.
Before treating any problem, review the steps to controlling pests and diseases [see: Flower and Bulb Pests and Diseases].
If the cure requires application of sprays or other control treatments, read completely and follow exactly the application directions found on the control’s package and label.
Only apply controls with labels that list the specific pest or disease you’ve found on your flowers. If in doubt about control choices and treatment methods, seek expert advice from your local university agricultural extension or knowledgeable staff of a garden center.
Common Flower Pests and Diseases
- Aphids >
- Anthracnose >
- Aster Yellows >
- Black Spot >
- Botrytis >
- Caterpillars >
- Crown Rot >
- Cutworms >
- Deer/Rodents >
- Earwigs >
- Leaf Gall >
- Leaf Hoppers >
- Leaf Miners >
- Leaf Spot >
- Mealybugs >
- Mosaic Virus >
- Nematodes >
- Plant Bugs >
- Powdery Mildew >
- Rust >
- Scale >
- Slugs/Snails >
- Soft Rot >
- Spider Mites >
- Stem Borers >
- Thrips >
- Whiteflies >
Symptom: Curled, twisted, sticky leaves; stunted or deformed blooms; loss of vigor. Sometimes found within tunic covering of lifted bulbs.
Cause: Aphids. Look for clusters of soft-bodied, round, black, gray, green, or yellow insects, 1/16–1/4 inch (1.5–6 mm) long. Found on many plants. Frequently found in combination with ants that milk them for their honeydew secretions.
Cure: Wash off light infestations with a strong stream of water. Release ladybird beetles, lacewings. If ineffective, dust with diatomaceous earth. Spray with a solution of 2–3 T (30–44 ml) of dishwashing liquid per gallon (4 l) of water. Spray with insecticidal soap.
Symptom: Black, tan, or red spots on leaves; leaves yellow and drop. Black cankers on stems, with a general wilt of branch tips.
Cause: Anthracnose. A fungal disease sometimes called black spot or twig blight. Occurs in late spring and summer, typically after humid conditions.
Cure: Remove infected leaves and branch tips. Collect and destroy infected fallen leaves. Thin excessive growth to promote air circulation. Spray with a fungicide as a last resort.
Symptom: White, yellow splotches appear on surface of leaves; leaves yellow and drop. Plants appear stunted, turn green yellow. Some flower petals may be green.
Cause: Aster yellows. Incurable viral disease of asters and other plants spread by aphids, leafhoppers.
Cure: Remove and destroy infected plants. Spray remaining plants weekly for 3 cycles with insecticidal soap.
Symptom: Leaves are mottled with black spots, eventually yellow and die.
Cause: Black spot. A fungal disease, found on many plants. Spreads by spores blown onto moist plant leaves.
Cure: Space plantings to allow good air circulation. Apply water at base of plant. Strip and destroy infected leaves. Spray with a solution of 1 part household bleach mixed with 9 parts water. Apply black-spot specific fungicide as a last resort.
Symptom: Flowers and foliage collapse under heavy fuzz of brown or gray fungal spores.
Cause: Botrytis rot, also known as gray mold, a fungal disease.
Cure: Remove affected blossoms, foliage, or entire plant. Space plants for more air circulation. Reduce or eliminate use of nitrogen fertilizer. Remove mulch. Water early in the day so foliage dries completely before evening.
Symptom: Foliage is eaten and stems are scored or eaten. Black or brown droppings, 1/20 in. (1.2 mm) wide are left on foliage. Moths and butterflies are seen resting on plants.
Cause: Various larvae and caterpillars, wormlike larvae, and loopers. Look at undersides of leaves and along stems for pests during midday.
Cure: Hand pick caterpillars from center leaves of plant. Release parasitic wasps and flies. Spray with Bacillus thuringiensis (BT). Apply horticultural oil.
Symptom: Brown stains and softened tissue near base of stem or crown of plant; leaves may yellow or drop.
Cause: Crown or stem rot. Look for brown rot at the central growth point where roots become foliage or decaying stems. Usually associated with keeping soil overly moist.
Cure: Rarely curable. Isolate plant to avoid spread to healthy plants. Remove infected foliage, dipping pruning shears in rubbing alcohol solution between cuts. Reduce watering. Repot to soil-free, well-drained mix. Take root cuttings of healthy growth to propagate into new plants.
Symptom: Germinating seedlings appear to be cut off nearly flush with the soil’s surface.
Cause: Cutworms. Look for smooth, gray-brown, wormlike moth larvae under plant debris or just below the soil surface.
Cure: Install cardboard collars, i.e., toilet-paper rolls, around plant stems, set 2 in. (50 mm) deep into the soil.
Symptom: Uprooted plants; foliage eaten to ground level; bulbs and roots eaten, leaving dying stalks and leaves.
Cause: Deer and rodents. Look for hoof and paw prints, burrows, mounds, and tunnels.
Cure: Plant resistant plants. Install fence barriers or cages when planting, including beneath-soil barriers [see Protecting Bulbs from Animal Pests]. Trap and remove rodents. Avoid bonemeal and fish emulsion fertilizers that attract animals by their strong smells.
Symptom: Chewed blossoms and petals, especially those with soft, fleshy parts.
Cause: Earwigs. Look for brown to black, segmented pests with sharp pincers extending from the rear part of their bodies.
Cure: Set out crumpled or rolled newspaper—earwigs will hide inside. Remove daily and discard with household trash. Apply diatomaceous earth earth. Apply moist bait containing carbaryl or spinosad.
Symptom: Leaves turn light green, are puffy, swollen, and distorted.
Cause: Leaf gall. A fungal disease common to azaleas, camellias, and rhododendrons.
Cure: Pick off and destroy affected leaves as soon as galls are noticed.
Symptom: Discolored leaves and plants. Leaves are puckered, curled, or twisted.
Cause: Leaf hoppers. Look for small, green wedge-shaped insects.
Cure: Spray with soap solution. Trap with sticky traps. Dust with diatomaceous earth. Spray with insecticidal soap. If problem persists, spray insects with horticultural oil to smother them.
Symptom: White trails on or inside leaves; papery yellow or brown blotches on foliage.
Cause: Leaf miners. Look for small, pale larvae and 1/6-in. (3.2-mm) tiny green or black flying insects.
Cure: Remove infested leaves. Move plant to sheltered outdoor spot and spray foliage with a solution of the botanical extract neem oil.
Symptom: Powdery black or brown dusting on foliage and blossoms. Leaves may drop.
Cause: Leaf spot, a fungal disease. Common in shaded, crowded plantings.
Cure: Remove shading foliage. Increase air circulation. Spray with a fungicide containing sulfur.
Symptom: Stunted plants; white cottony clusters in leaf axils or where leaves meet at bases of plants.
Cause: Mealybugs. Look in the junctions between leaves and stems or at the base of leaf clusters for white or gray, waxy bugs, 1/8-in. (3-mm) long.
Cure: Dab or spray with rubbing alcohol solution diluted 3:1 with water; spray with insecticidal soap; spray with horticultural oil.
Symptom: Streaked and mottled foliage, deformed blooms; stunting; loss of vigor.
Cause: Mosaic virus, an incurable plant disease.
Cure: Remove bulbs and dispose of affected plants, do not compost. Promptly control aphid, spider mite, and thrip infestations, that can spread viral infection. Plant mosaic-virus resistant species and cultivars.
Symptom: Stunted, discolored, or spotted plants with deformed roots, sometimes bearing swollen galls; loss of vigor.
Cause: Soil nematodes, near-microscopic wormlike creatures that live in soil and feed on plant roots and bulbs.
Cure: Release beneficial nematodes. Remove and destroy infested plants. Solarize bed for 3–4 weeks prior to planting by covering soil with clear plastic and allowing sunlight to raise soil temperature to 140°F (60°C). Replant with unrelated species.
Symptom: Leaves with brown or black spots. Roots and shoots may be deformed.
Cause: Plant bugs, true bugs rather than insects. Look for greenish-yellow insects 1/4-in. (6-mm) long.
Cure: Hand pick. Spray insects with insecticidal soap. Apply pyrethrin or rotenone as a last resort.
Symptom: Light powdery dusting of gray or white on leaves, flowers; deformed new growth; stunting; loss of vigor.
Cause: Powdery mildew, a fungal disease often found when days are hot and humid days and cool nights alternate. Mostly attacks new leaves.
Cure: Remove shading foliage. Improve air circulation. Dust with sulfur. Spray with a solution of baking soda (sodium bicarbonate) and horticultural oil: 1 tablespoon (15 ml) baking soda and 3 tablespoons (44 ml) horticultural oil per gallon [4 l] of water.
Symptom: Tops of leaves are marked with pale spots, undersides have brown, red, round spots. Leaves may brown and drop.
Cause: Test leaf by wiping underside on white cloth. Orange or pink stains signify rust, a fungal disease that produces raised pustules that ripen, rupture, and release powdery, orange to red-colored spores that spread the infection.
Cure: Plant resistant cultivars. Eliminate overhead watering. Fertilize with nitrogen monthly until symptoms subside.
Symptom: Stunted, yellow plants lacking vigor; leaves may drop.
Cause: Scale. Look for 1/20-in. (1.2-mm) flylike insects accompanying soft or hard 1/50-in. (0.5-mm) mounded bumps on stems and leaves.
Cure: Remove infested foliage. Swab scales with soapy water or dilute denatured alcohol solution; rinse well after solution dries. Apply horticultural oil. Spray with pyrethrin or rotenone as a last resort.
Symptom:Chewed leaves and blossoms; silvery mucus trails.
Cause: Slugs and snails. After dark, look for shelled and unshelled mollusks on foliage or soil.
Cure: Remove leaf litter, a common hiding place. Hand pick after dark; use copper foil barriers around beds or containers; dust with diatomaceous earth; use beer-filled traps; use non-toxic baits containing iron phosphate; use bait gel.
Symptom: Center of plant becomes soft and turns brown. Strong, unpleasant odor is present from diseased plant tissue.
Cause: Soft rot. A bacterial disease, usually begun on bruised plant tissue. Usually incurable.
Cure: Remove, bag, and destroy infected plants by burning or in household waste. Avoid replanting the same species in infected soil for 2–3 years.
Symptom: Leaves develop speckles, wrinkle, turn yellow, and drop. Tiny white webs coat leaf undersides, basal junctions.
Cause: Spider mites. Shake foliage and blossoms over white paper and look for moving red or yellow, spiderlike specks. Thrive in hot, dry conditions.
Cure: Release lady bird beetles. Spray repeatedly with a strong stream of water to rinse off dustlike pests; spray only infested plants with insecticidal soap. Avoid use of sprays that kill natural spider-mite predators or widespread spraying beyond immediately infested plants.
Symptom: Spotted, sometimes semi-translucent leaves. Frequently found with fungal disease.
Cause: Stem borers. Look on foliage, roots for segmented larvae and caterpillars, 1/2–1-in. (12–25-mm) long. In gardens near corn-farming production, corn borer may infest dahlia and gladiolus.
Cure: Hand pick. apply Bacillus thuringensis (BT) to affected foliage. Remove and destroy infested foliage.
Symptom: Brown-, silver-, or white-speckled leaves. Foliage may feel gummy or be deformed. Blooms are deformed and fail to open.
Cause: Thrips. Shake foliage and blossoms over white paper and look for moving, winged specks. Thrive in hot, dry conditions.
Cure: Release lady bird beetles. Remove and destroy infested foliage. Wash foliage with a strong stream of water. Spray pests on infested plants with insecticidal soap.
Symptom: Yellow leaves and stunted, sticky plants. When foliage is disturbed, white insects may fly out in a cloud surrounding the plant.
Cause: Whiteflies. Shake foliage and look for 1/20-in. (1.2-mm) mothlike flying insects. Inspect leaf undersides for scalelike, gray or yellow eggs.
Cure: Catch with sticky panel traps. Spray with soap solution. Spray infested foliage with insecticidal soap. Move plant to sheltered outdoor spot and spray foliage with horticultural oil or neem oil extract solution. Spray with pyrethrin as a last resort.
> Next: Bulb Pest and Disease Solutions