Bulbs are surprisingly resistant to pests and disease than are many other flowering plants, but you should still remain vigilant: Begin your control of pests and diseases with good gardening practices designed to reduce the chance of infestations or infections. Block the growth of weeds that host insect pests and fungal spores by mulching your beds or planting groundcovers; promptly remove any weeds that emerge. Rid your garden of fallen leaves, plant debris, pruning litter and dead foliage to eliminate the favorite hiding spots of slugs and snails, two of the most significant bulb pests. Garden debris shelters eggs, larvae, grubs and adult insect pests, as well as nematodes and many plant bacteria, viruses and fungal spores.

Friend or foe? About 95 percent of the insects found in your garden are either beneficial or harmless. Many bulb plants are resistant naturally to many insect pests, which you can control with simple means such as washing them off with a sharp stream of water.

Photo Credit: ©2002 Dolezal Publishing/John M. Rickard

Ladybird beetles – or ladybugs – are one of the “good guys.” They eat several times their weight in aphids each day!

Photo Credit: ©2002 Dolezal Publishing/John M. Rickard

One way to dispose of garden waste and put it to good use is by composting it. The heat of vegetative decomposition renders most pests and weed seeds inert, leaving you with rich organic compost that can help your garden grow. Organic compost contains beneficial living organisms, and it provides major and trace nutrients to feed your plants. It’s also a great soil conditioner for improving soils that are too clayey or sandy.

Next, take advantage of the disease and pest resistance of some bulb species. Narcissus, for example, have natural defenses against fungus, insect and animal attack. Good cultural practices by professional growers mean that bulbs are vigorously checked while in product fields so they’re in good health and free from pests and disease when they arrive at the garden center, nursery and home garden. Using care to avoid cuts and nicks during planting and cultivating further helps to keep fungal disease spores from entering the bulb.

Still, sometimes pests gain a foothold. Ants, aphids, Japanese beetles, various borers, mites, mollusks (slugs and snails), harmful nematodes, thrips, whiteflies, and wireworms feed on bulbous plants. Some bulbs are also susceptible to botrytis, mildew and viral diseases.

Most horticulturists refer to the USDA’s guidelines for Integrated Pest Management (IPM) to keep infections and infestations to a minimum. IPM calls for frequent inspections to discover outbreaks before they become widespread, followed by the use of hand controls – picking, crushing, washing with plain water, and the like – to eliminate the condition without using harmful chemicals. Persistent conditions are first treated with biological measures: releasing ladybird beetles to eat aphids, applying beneficial nematodes to the soil, or spot-spraying solutions containing Bacillus thuringiensis (Bt), then by using mild, environmentally protective controls such as household and insecticidal soaps that smother or dissolve pest tissues. These sequential steps can typically control most insects and diseases.

Only the most severe, sustained outbreaks should be treated with pest-specific pesticides and fungicides. If such care 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 dispose properly of any unused solution and empty containers.

The goal of IPM is to limit damage to the garden while protecting the environment and maintaining a healthy ecological balance between insect pests and predators. Pests reproduce more rapidly than do predators, so maintaining a healthy population of “good bug” predators assures that pest insects are kept to a minimum.

Unfortunately, viral diseases (like mosaic virus) resist treatment. If your bulbs contract a virus, lift and discard them to prevent spreading. (Do not add these plants to the compost pile!) The good news is that most bulb diseases can be controlled. Most are caused by fungus or mold, and they’re more common in cool, damp weather. You can help prevent plant diseases by watering early in the day and allowing foliage to dry thoroughly before sunset.

If your bulbs experience an outbreak of disease that you can’t control, you’ll need a fungicide that’s properly listed for your plant problem and specific bulb species, a plastic spray applicator, eye protection, rubber gloves and waterproof clothing, as needed. For best results, carefully read and follow all product instructions completely. On a wind-free day, fill your spray applicator with the correctly diluted solution. Spray only the affected plants, wetting the tops and undersides of all infected foliage. Avoid overspraying. (“More” does not mean “better.”) When you’re finished, safely empty the sprayer and wash it and your gloves with warm, soapy water. Always safely dispose of unused solution, the wash water and empty garden chemical containers.

Insecticidal soaps, when used alone or in combination with plant-derived pesticides such as pyrethrin, kill pests by interfering with their breathing or by dissolving their cell walls. To be effective, they must be applied directly to the pest. Use them only when an infestation continues after using hand-control methods, biological controls and washing with plain water. You’ll need an insecticidal soap that lists both the specific condition to be treated and your plant species, a plastic spray applicator, eye protection, rubber gloves and waterproof clothing. To choose a control and apply insecticidal soap, follow the instructions shown in the following pictures and described in their captions.