Thrips on Spring Bulbs: How to Spot Them and Get Rid of Them

Silvery speckles on a leaf, or petals that look scuffed before they open, often point to a pest too small to notice at first glance. Thrips feed on spring bulbs and their relatives through the growing season, and the damage shows up well before the insects do. Knowing what the scarring looks like, and where the insects hide, makes them manageable.

Thrips: What You See

The insect itself is hard to spot, so the damage is usually what gives it away.

• Silver or bronze speckles on the surface of leaves or petals come from species that inject digestive enzymes into the wound as they feed.
• Leaves that look scarred and stippled, then twist or crinkle because they stop elongating properly, are the usual sign in Kentucky.
• The insects are slim, winged and only about 1/20 of an inch long, so they look like moving specks.
• Look low in the plant, where young leaves gather in the inner neck, because young and adult thrips both settle there.
• On gladiolus, look at the flowers and the corms, where gladiolus thrips gather, with dark bodies and grayish wings.

Warm spring weather is when adults start flying to new plantings, so that is the time to start checking.

Thrips or Something Else?

Silvery stippling is not a signature that belongs to thrips alone. Other small pests leave a similar pattern, and treating the wrong one wastes effort.

A quick test helps. Hold a sheet of white paper under a leaf, tap the leaf, and watch what falls and moves.

Cold or dry spells can also leave pale, scuffed leaves, but those marks show up on a whole bed at once and no insects turn up on the paper.

What Causes Thrips, and Where It Is Worst

Thrips arrive on their own. They have a broad host range, so weeds, crop debris and neighboring plants all keep them nearby. Weeds inside or outside a high tunnel can harbor them, and in mild climates they overwinter as adults or larvae on debris and weeds, ready for spring.

Warmth speeds them up. Their populations increase rapidly under hot, arid conditions. In Kentucky, development from egg to adult can take as little as 20 days, and a single year can bring 6 to 8 generations, so a few insects in spring can become a crowd by summer. In Utah, adults fly to new onion plantings once spring temperatures warm.

Gladiolus thrips follow a different pattern. This tropical species will not survive temperatures colder than 50° F (10° C), so in cold-winter yards it carries over on stored corms, bulbs, or plants kept in a greenhouse. They also infest iris, lily, and other plants grown from tubers and bulbs.

How to Treat Thrips

Start with the cheapest steps, and work toward anything stronger only if the damage keeps spreading.

1. Inspect the inner neck of the plants and the youngest leaves, so that you confirm thrips before doing anything else.
2. Pull weeds around the bed and along its edges, so that the insects lose a place to live and breed.
3. Clear plant debris from the bed, so that adults and larvae have nowhere to wait out the cool months.
4. Hang blue or yellow sticky traps near the plants, so that you can see whether numbers are rising or falling.
5. Look over gladiolus corms and bulbs that you handle, so that infested ones do not carry the pest into next season.
6. Contact your state extension service about what is approved in your state, so that any spray you choose is legal and suited to your plants.

Timing matters because the life cycle moves quickly. In Kentucky, females insert eggs into plant tissue and the nymphs emerge 4 to 10 days later. The young feed for 5 to 7 days before dropping into the soil to pupate. Keep checking regularly instead of treating once and walking away. Leave green foliage alone: the leaves are still feeding the bulb for next year, even when they look scuffed.

How to Prevent Thrips Coming Back

Prevention follows the calendar, because thrips move with the weather and the state of the bed.

• In early spring, pull weeds in and around the bed before adults begin flying to new plantings.
• Once the weather warms, set out sticky traps and look at them regularly, since numbers climb fast in warm, dry spells.
• Through the growing season, check the inner neck of the plants now and then, because young leaves there are where thrips like to feed.
• After the leaves have turned yellow and withered, clear the debris from the bed so overwintering adults and larvae lose their cover.
• At lifting time in fall, look over gladiolus corms and any other bulbs you dig before they go into storage.
• In winter, keep greenhouse plants away from stored corms and bulbs, since thrips can overwinter on either.

Any bulb still unplanted can go in as soon as the ground can be dug, and a clean bed gives it a better start.

Where This Comes From

The details here come from university extension pages written for Kentucky, Utah and Virginia, and timing can differ in your yard. Your state’s extension service can tell you which thrips are active locally and what is approved for use there.

Common Questions

Do Thrips Spread Disease in the Garden?

They often carry plant diseases from one plant to the next as they scrape and suck plant fluids. That is one more reason to deal with them early, even when the visible scarring looks minor.

Are Thrips Attracted to Flowers?

Adults are drawn to flower pollen. Even so, young and adult thrips mostly feed on plant tissue, using rasping and sucking mouthparts to draw out plant fluids, so leaves are damaged too.

Can Thrips Hurt Onions Growing Near Your Bulbs?

Yes. Thrips damage to bulb onions costs yield and storage quality, and the early stage of bulb development is when the plants are most sensitive. Check onions and ornamentals alike when you see speckling.