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Although bulbs tend to be somewhat resistant to pests and diseases, infestations still occur. Before treating any plant problem, take the time to properly assess the situation and positively identify the pest or disease attacking your specific bulbs. Use the following chart to help identify plant symptoms, causes and remedies for your blooming bulbs.
 Before treating any fungal disease, identify the kind that’s affecting your bulbs (or any plant). If necessary, consult experienced staff at your local garden center, nursery or Cooperative Extension. Choose a control that’s approved for use on your bulb plants. Photo Credit: ©2002 Dolezal Publishing/John M. Rickard  On a wind-free day, fill your spray applicator with correctly diluted solution. Spray only the affected plants, wetting the tops and undersides of all foliage. Avoid overspraying. (“More” does not mean “better.”) Photo Credit: ©2002 Dolezal Publishing/John M. Rickard
Symptoms: 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 1⁄16-inch, black, green, yellow or gray, round insects. Frequently found in association with ants, which milk them for their honeydew secretions
Remedies: Release ladybird beetles, lacewings. Spray with water from a hose; spray with solution of 2-3 tablespoon dishwashing liquid per gallon of water; try insecticidal soap.
Symptoms: Spotted, sometimes semi-translucent leaves, frequently accompanied by fungal disease.
Cause: Stem borers. Look on foliage and roots for segmented larvae and caterpillars, ½-1 inch long. In corn-farming regions, corn borer may infest dahlia and gladiolus.
Remedies: Hand-pick; apply Bacillus thuringensis (bt) to affected foliage. Remove and destroy infested foliage.
Symptoms: Stunted plants; white, cottony clusters in leaf axils.
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 an inch long.
Remedies: Dab or spray with rubbing alcohol diluted 3:1; spray with insecticidal soap or horticultural oil.
Symptoms: Stunted, discolored, spotted plants with deformed roots, sometimes bearing swollen galls; loss of vigor.
Cause: Nematodes. Microscopic, wormlike creatures that live in soil and feed on plant roots.
Remedies: Release beneficial nematodes. Remove and destroy affected plants. Replant with unrelated species. Solarize planting bed for 3-4 weeks prior to planting by covering soil with clear plastic and allowing sunlight to raise soil temperature to 140 degrees F.
Symptoms: Leaves speckle, wrinkle, turn yellow, drop; minute white webs are seen on undersides and at 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.
Remedies: Release ladybird beetles. Spray repeatedly with water to rinse off dustlike pests; spray with insecticidal soap. Avoid using any spray that also kills natural predators.
Symptoms: Brown-, silver- or white-speckled leaves; may be gummy or 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.
Remedies: Remove and destroy infested foliage. Release ladybird beetles. Spray with water; spray with insecticidal soap. Avoid using any spray that also kills natural predators.
Symptoms: Chewed leaves and blossoms; silvery mucus trails.
Cause: Slugs and snails. Look after dark for shelled and unshelled mollusks on foliage or soil.
Remedies: Remove leaf litter, which the pests use as hiding places. Hand-pick after dark; use copper foil barriers around beds or containers; dust with diatomaceous earth; use nontoxic baits containing iron phosphate; try bait gel.
Symptoms: Uprooted plants; foliage eaten to ground level; bulbs and roots eaten, leaving dying foliage stalks and leaves.
Cause: Deer and rodents. Look for hoof and paw prints, burrows, mounds, tunnels.
Remedies: Plant deer-resistant bulb types. Install fence barriers or cages when planting, including beneath-soil barriers. Trap and remove small animals. Avoid bonemeal use.
Symptoms: Browning flowers and foliage collapse under heavy fuzz of gray or brown fungal spores.
Cause: Botrytis – also known as gray mold, a fungal disease. Common in warm, humid weather.
Remedies: Remove affected blossoms, foliage or the entire plant; space plants for more air circulation; reduce nitrogen fertilizer; remove mulch; water early in the day to allow complete drying before nightfall.
Symptoms: Powdery black or brown dusting on foliage and blossoms; leaves may drop.
Cause: Leafspot – fungal disease. Common in shady, massed plantings.
Remedies: Remove shading foliage, increase air circulation; carefully spray with sulfur fungicide.
Symptoms: Light powdery dusting of gray or white on leaves and/or flowers; deformed new growth; stunting; loss of vigor.
Cause: Powdery mildew – a fungal disease. Common if humid, warm days and cool nights alternate.
Remedies: Remove shading foliage, increase air circulation; spray affected plants with solution of 1 tablespoon baking soda and 3 tablespoons horticultural oil to 1 gallon of water; dust with sulfur.
Symptoms: Streaked and mottled foliage; deformed blooms; stunting; loss of vigor.
Cause: Mosaic virus – an incurable plant disease.
Remedies: Remove and destroy affected plants. Promptly control aphid, spider mite and thrip infestations, which can spread viral infection. Plant resistant bulb types.
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