How to protect your growing bulbs and plants from nasty pests - East Idaho News
In the Garden

How to protect your growing bulbs and plants from nasty pests

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Continuing on the topic of bulbs, let’s cover some of the challenges related to growing bulbs.

It seems as though spring flowering bulbs are fairly trouble-free. However, if your bulbs are not crowded and the flowers or stems are stunted or the flowers just come out wilted with no real bloom, we may want to consider the possibility of insect and arachnid (arthropod) pests.

As we discuss potential pests, keep in mind that there are many beneficial arthropods that will help keep the pests under control. Beneficial arthropods that may help keep pest populations manageable include but are not limited to: ladybugs, green and brown lacewings, damsel bugs, minute pirate bugs, big-eyed bugs, ground beetles, predatory thrips, red velvet mites, spiders, collops beetles, rove beetles, aphid predatory midges, hover flies, parasitoid wasps, and ambush and assassin bugs. Control programs
should be designed to identify, preserve and encourage these beneficial predators and parasitoids.

Whitney Cranshaw Colorado State University 01
Whitney Cranshaw | Colorado State University,

Treating with broad-spectrum insecticides will often do more damage to the beneficial population than the pest population. If you choose a chemical intervention, be sure the pest and target plant are listed on the label. ALWAYS READ AND FOLLOW THE LABEL.

Here are some “soft” treatment options that tend to be less damaging to beneficial arthropods.


Aphids feed on the upper parts of the plant, which may show up as deformed leaves and flowers. They can usually be found in feeding clusters on new growth, and may do significant damage before the predatory insects arrive.

Aphids have many natural enemies. The most environmentally friendly treatment for aphids is a stiff spray of water to knock them off the plant. Insecticidal soap is also quite effective on aphids.

Bulb mites

Bulb mites are very tine and feed on the bulbs rather than the flowers and leaves. They tend to be a secondary pest, taking advantage of something else that has weakened or damaged the bulb. Infested bulbs will have soft spots and the weakened plants will be stunted and off-color with deformed flowers.

Examine all bulbs when they are planted or stored. Avoid planting in soils that have had bulb mite infestations. Dipping dormant bulbs in 120⁰F water for 2 minutes can kill bulb mites. No pesticides are listed for bulb mite control.


The most common thrips that infest flowering bulbs are the gladiolus thrips, onion thrips and western flower thrips. Feeding damage may be from brown or silvery specks or streaks to heavily distorted leaves and flowers.

Thrips have several natural enemies. Small, yellow or blue sticky cards can be placed among the bulb plants to trap thrips that are attracted to the bright colors. Insecticidal soap can be effective with a thorough coverage.

Bulb flies

Bulb fly maggots burrow into the bulb near the basal plate and feed on the bulb. The result is soft, brown and decayed bulbs. Plants may be yellow and distorted Females lay eggs near the bulbs in May –early-June.

Plant only firm, healthy bulbs. Infested bulbs can be submerged in water maintained at 110⁰F for 40 minutes to kill the maggots, but it is easier to remove and destroy infested bulbs.

If your bulbs are not thriving, try some of these practices to encourage vibrant spring colors.