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How to Check Growing Onions for Bugs

With any plant growing in your garden, onions are subject to a number of pests. While onions deter some insects and larger pests like deer and mice, some persistent pests will still attempt to wreak havoc on your onion patch. So how can you tell when pests are harming your onions before the damage is already done? Keep reading to find out how to check your growing onions for bugs, and what pests to keep an eye out for. 
Three photo collage with largest photo of an up close image of garlic bulbs growing in the soil, and a smaller image of a ladybug on a leaf, and a spider mite on a leaf

Onions are part of the allium family, “a genus of monocotyledonous flowering plants that includes hundreds of species, including the cultivated onion, garlic, scallion, shallot, leek, and chives”[5]. Alliums have a high sulfur content[4] which can act as a deterrent to many pests, including insects, and can even protect other plants in their vicinity from harmful bugs. However, there are some pests that are simply more difficult to keep away and will make a meal out of your onion patch. 

How do you check growing onions for bugs?

Up close image of an onion green covered in small bites created by insects


What are thrips? 

Thrips are very small insects that gobble up a variety of plants. They are about the width of a sewing needle, so the damage they create is more easily identifiable than the insect itself. Thrips not only eat plants in the garden, like onion greens, but they also transmit disease. 

How do you check your onion plant for thrips?

Because thrips are so tiny, it’s easier to identify the damage they leave behind than the insects themselves. The insects are slender and yellow or black, and can often go unnoticed. You should look out for graying leaves[4], or transparent and silver patches on your onion leaves. Luckily, thrips can be identified just by examining your onion plant’s leaves. If you notice these traits, you may have a thrip infestation. 

Spider Mites

What are spider mites?

Spider mites are tiny pests, but are in fact not insects. They are actually a part of the arachnid family. Spider mites are sucking pests[3] and will attack both outdoor and indoor house plants. Most species of spider mites are actually repelled by allium plants like onions, however, the “two-spotted spider mite – also known as the red mite – is ridiculously fond of onions”[2]. They are small, round, reddish brown specks that can be difficult to see unless you know where to look for them. 

How do you check your onion plant for spider mites?

Individual spider mites can be hard to spot, but luckily, or rather unluckily they typically live in colonies, which can be great for spotting them, but bad for your plants. Most commonly they can be found on the underside of leaves[3]. To check your onion plants for spider mites, check the underside of the leaves for reddish-brown speckles. You can also identify a spider mite infestation by the damage they leave behind. Check your onion greens for small light-colored dots along the leaves. Your leaves may also begin to turn yellow and die. 

Trail of bite marks from a leaf miner insect on a dark green leaf

Leaf Miners

What are leaf miners?

Leaf miners are another common onion plant pest. Leaf miners will attack your onion plants in their larval stage[6] in which they can consume large amounts of leaf tissue. Leaf miners are very difficult to see, but they leave behind a distinctive trail that clearly indicates their presence in your garden. 

How do you check onion plants for leaf miners?

Leaf miners are tiny and hard to see larvae, but they do make themselves known by the destruction they cause. They are fittingly named leaf miners as they leave behind a spotted trail of bite marks. If you spot swirling and light-colored trailing patterns on your onion leaves, you definitely have a leaf miner problem. Be sure to cut away the affected area and burn, or soak them in soapy water and discard. 

Bulb Maggots

What are bulb maggots?

Bulb maggots are maggots or fly larvae that make a home for themselves in your onion bulbs. Maggots occur when flies lay their eggs in the soil at the base of the onions. “When the eggs hatch, the maggots burrow into the bulbs and eat their way through them as they mature”[2] making for a very disappointing harvest. 

How do you check onion plants for maggots?

Unfortunately, bulb maggots cannot be identified until your onions have been harvested. You’ll have to cut into the bulb to identify these horrible pests. Maggots cannot be identified until it’s too late, but they can be prevented. To prevent maggots from flocking to your onion bulbs, avoid overwatering your onion plants. Additionally, you should rotate crops, being sure to not plant members of the allium family in the same plot two years in a row. 

How do you remove bugs from growing onion plants?

As we’ve learned, there are unfortunately a number of pests that enjoy onion plants, despite their intense flavor, and high sulfur content. Luckily, there are a number of ways to remove and prevent bugs from devouring your onion plants. 

Manually remove pests

It sounds obvious, but you can actually effectively remove pests by simply picking them off your plant. Wearing gardening gloves, pick off any visible bugs and “destroy pests by drowning them in a bucket of soapy water or crushing them with your foot”[1]. 

Safer Brand 5110-6 Insect Killing Soap, 32 Oz.

Use an insecticide soap

Insecticidal soap is an organic material used by many gardeners to gently remove and deter pests from onion plants and beyond. The potassium salts in the insecticidal soap will work to “remove an insect’s protective waxes, causing destruction of insect membranes and killing them”[1]. This will work for insects that live on the leaves of onion plants but will not affect maggots or larger pests like birds. 

Keep pests away from your onion plants

The best way for you to save your onion plants from pests is to deter them entirely by making a difficult environment for them to thrive. Many pests are attracted to decay, so keep your garden bed free of dead or decaying plant parts or fallen leaves. Additionally, you can use tinfoil to protect your onion plants further. Many pests start from the bulb and work their way up to the greens of the plant to have a feast. By wrapping the bottom stem of your onion plant in tinfoil[1] just above the bulb, bugs will have a much more difficult time climbing to the top.

TomorrowSeeds - 3 Colors Mix Onion Sets (Bulbs) Yellow, Red, White Sweet Onions Set for Growing Gardening Noon Day Vegetable Seed for 2022 - 1 Pound


Article Sources:

  1. Food Gardening Network. “What to Do About Pests that Can Harm Your Onion Plants
  2. Morning Chores. “How to Identify and Treat Common Onion Pests and Diseases
  3. Planet Natural. “Spider Mite
  4. Starkbros. “Pest & Disease Control for Onion Plants
  5. Wikipedia. “Allium
  6. Wikipedia. “Leaf Miner