Bulb Pests and Diseases: Symptoms, Causes and Cures

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Robert J. Dolezal

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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.

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.

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.

Warnings

Chemical use is best avoided for the overall good of the environment, family and pets. If spaying is absolutely necessary, choose a control that lists both the specific pest/disease problem and the specific plant the product is intended for. Always read and completely follow all package directions for mixing, diluting, timing, frequency and method of applying the control. Wear protective clothing and a respirator, apply the agent on a wind-free day and as directions state – avoiding broadcast application – and properly dispose of any unused solution and empty containers.

Tips

Want to keep the pests away using natural methods and with as little chemicals as possible? Practice Integrated Pest Management (IPM)! This popular method of pest control includes routinely inspecting plants for pests, growing pest-resistant plant varieties and implementing good cultural practices in the garden.
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Have a question about controlling pests and diseases? Come to The Garden Party and post it in the L2G Forums for our gardening experts and other knowledgeable home gardeners to answer.

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