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How to Prevent Bugs From Killing Your Growing Onions (All Options)?

Onions are one of the oldest plants in the home garden. Onion family plants come in a varieties. All are suffer by the same bugs and diseases. Preventing onion bugs is an important part of garden maintenance. Here's a guide on how to prevent bugs from killing your growing onions.

Ways tp prevent bugs killing onion plants.

I learned from grubbing in my parents’ vegetable garden when I was a kid that bugs are the scourge of the world. You have mosquitoes that target people. You have termites that target your house. In gardens, it’s mites, slugs, nematodes, and dozens more, plus animals.

I also learned that gardens are a full-time job. They have to have weeds pulled, they have to be treated for bugs, they need copious amounts of water, and they have to have animals kept out of them. In middle Tennessee, it was deer that got into the vegetable garden, so we had to keep the shotgun handy.

So, what is it about bugs and onions? First, we need to know why onions attract the attention of all and sundry. Then we need to know what bugs are attracted to the onions. Then, we need tips and hacks on how to get rid of bugs. Ready to learn more about your onions?

Why Do Onions Attract Bugs’ Attention?

Large onion plants in garden.

The answer to that question lies in bulbs in general, such as flower bulbs (tulip, crocus, daffodil, and many more) and food bulbs (onion, garlic, tubers like carrot and potato.) The reason is that the bulbs and tubers store the energy needed for future development and flowers. Bugs feed on that energy, so, of course, they’re attracted to onions and other bulbs.

The energy is stored in the layers that make up onions, garlic, and other bulbs. The root system supports this storage, which is why you’ll almost always see roots accompanying bulbs you buy at the grocery store or a farmer’s market.

Take an onion, for example. When you slice it in half and see the circles, those circles are actually leaves whose purpose is to hold food used by the bulb while it lies dormant (bulbs planted in late fall lie dormant over the winter.) 

The food storage of a bulb is necessary for the bulb to withstand adverse conditions before or during its dormancy. This includes severe late fall or winter weather such as backlash from hurricanes or vicious winter storms. The bulbs count on that food and energy storage to get them through the worst of it. When spring comes, the real growth can begin.

What Bugs are Attracted to Onions?

From the microscopic to the plainly visible, a variety of bugs want to eat your onions. Let’s take a look at bugs.

Bulb Mites

It’s not just your onions that mites love. It’s any bulb from garlic and onions to crocus, lilies, tulips and freesias. They’re tiny, and I mean microscopic. They don’t live long; the females die off after a month with the males soon after mating. However, that’s long enough for them to infest your crop, either in your garden or in storage.

Wheat Curl Mites

This tiny guy prefers eating your onions where they’re stored. He also eats tulips, garlic, corn, wheat, and some grains and wild grasses. When these mites work on onions, they cause the bulbs to rot. They also carry viruses that infect a crop, but generally these are grains or corn.

Onion Maggots

Onion maggots attacked onion bulb.

Onion maggots are the larvae of the small gray fly. The eggs are laid near seedlings just beginning to grow. They prefer organic matter mixed with the soil, such as compost that isn’t decomposed yet. The maggots eat the roots and developing plants along with infesting the bulbs just beginning to grow.

Nematodes

There are beneficial nematodes that eat up pests infesting your garden. There are also nematodes that infest your garden. They’re not good or beneficial. They, too, are microscopic. They’re roundworms that live inside the plants, in the soil, and they feed on bulbs, roots, and stems. When they’ve gotten through the onion’s skin, they allow fungi and pathogens to get into the bulb, causing it to rot.

Thrips

Black thrips crawling on a leaf.

Also microscopic, thrips winter in the remains of fields plowed for crops, tossed-out greenhouse remains, along with the remains of your vegetable garden. They propagate at an alarming rate, with several generations living in one year. 

Thrips tear open the cell walls of the onion to feed on the juices. They prefer hot weather, but lots of rain or a sudden dip in temperatures will kill them off. They look like little silver lines or white patches on leaves and cause slow growth of the onion.

Leek Moth

About the size of an ordinary moth, this pest lives in Eastern Canada, New York, and Vermont, but not yet in the remainder of the northeast. The moth tunnels its way down the hollow tubes of the onion leaves, eating what is offered internally. Onions suffering from this pest are susceptible to pathogens and live generally on the edges of fields.

Black Aphids

Black aphids on a leaf.

Black aphids don’t lay eggs; they produce their young in a long black line on the leaves and stalks of your onions. They do this every couple of days and can produce up to five lines of young every five days. The weird part is that all the young are female.

The pests overwinter in the warmest spots in your vegetable garden while they wait for your crop to begin producing. When it gets warm enough, they’ll suddenly pop out, making you think they came from nowhere. They were actually there all along.

When the first young, vulnerable leaves appear on your onions, the aphids suck the life out of them. The young leaves contain the carbohydrates aphids need the most, which is why it’s called an infestation.

Leaf Miners

These pests feed on the inside of leaves. They leave patches or meandering tunnels of dead tissue behind. They don’t necessarily affect the growth of the bulb, but they do kill off the edible parts of the plant. Since they feed on the inside of the plant’s leaves, you won’t see them. Watch for the winding pathways and dead leaves.

How To Prevent Bugs From Killing Your Growing Onions?

Onion in the garden with diseases.

There are two ways of preventing the death of your onion crop. Many chemical pesticides have been banned due to their adverse effects on foods, animals, and humans. Lots of chemicals have been developed that kill bugs but don’t harm food, animals, or humans. You’ll find these in any garden center or hardware store.

The second way is the natural method of killing bugs. This method falls into two categories: planting bug-repellent foods around your onions, and using herbs or essential oils or a combination of the two in water and spraying it on your onions and other foods. Let’s take chemicals first.

1. Chemical Pesticides

Ortho MAX Malathion Insect Spray Concentrate, 16 oz.

Three types of pest control are used in what we commonly call pesticides: herbicides, fungicides, and insecticides. There are alarmingly few pesticides for use on onions, but the ones that do exist aren’t very effective. These pesticides leave thrips, maggots of various types, and worms of various types to feed on the onions. You can read the list here.

The pesticides available seem to be only for use on leeks, shallots, and garlic. I did manage to find a list of pesticides for use on onions in Utah, complete with brand names. You can read the list here, but I’ll describe one brand of pesticide for you to give you an example:

Ortho MAX Malathion Insect Spray. Amazon, not expensive. It kills aphids, mites, mealybugs, flies, thrips, and other pests. It can also be bought at big box stores like Lowe’s and ACE Hardware. Do some research on the brand manufacturer to discover if the pesticide is recommended for use in your neck of the woods.

2. Natural Pesticides

Herbal And Essential Oil Solutions For Onion Pesticides

Insecticide spraying onion plant in pot.

Herbs and essential oils possess great health benefits for us, but they’re deadly to bugs. There’s just something about the smell of certain herbs and essential oils that keep bugs away from your onions. Try this:

    • Get out the blender. Into it place two garlic cloves and four mint leaves, including stems. Place one half cup water in the blender and make sure the whole thing is liquefied. Place the mixture in a spray bottle and spray your onions. The kicker is that bugs hate the smell of mint, and added garlic just gives bugs a complete headache.

    • For an added kick, add ten drops each of lavender essential oil and citronella essential oil to the mix. Shake well and spray your onion plants.

    • Get a spray bottle and into it add 20 drops each of thyme, peppermint, white fir, cedarwood, spearmint, and lemongrass essential oils. Fill the rest of the bottle up with witch hazel and shake well. Spray your onion plants  every three to four days.

    • The list of essential oils used in commercially prepared pesticides can be used by home gardeners and includes: thyme, citrous, geranium, lemongrass, cedarwood, cinnamon, cloves, peppermint, garlic, rosemary, sesame, and eucalyptus. 

    • The list of herbs used in homegrown pesticides includes mint, basil, lavender, chives, rosemary, dill, sage, garlic, chives, and marigold, among dozens of others. 

Note: You’ll want to wash your onions very carefully following the use of these herbal and essential oil pesticides. I don’t know about you, but I’d rather not bite into an onion slice smelling or tasting like citronella.

Other Natural Methods Of Onion Pesticides

Simple dishwashing soap contains insecticidal resources. Mix one tablespoon with one quart of water. Shake well and apply to your onion plants. You should do this every three to four days in the cool of the evening.

This may seem funny, since you’ll be spraying it on onion plants, but it’s a well-known natural pesticide. Take four cloves of garlic, one medium onion, and one teaspoon of cayenne powder. Liquify them in a blender. Mix with water and put it in a spray bottle. Spray your onions with this mixture every three to four days.

Slugs love to snuggle beneath the dirt and mulch in gardens. When the evening comes, they emerge to chow down on your onions.

Prevent their dining out by placing a small plastic cup in the soil until only an inch or so remains above ground. Pour a cheap can of beer into the cup. The slugs will head for it every time, and that’ll be the end of that.

3. Plants as Pesticides

Different types of herbs in raised bed garden.

You can plant certain vegetables, herbs, and even flowers next to your onions as a pest repellent. While the strong smell of the onion repels pests from other veggies and flowers, they, in turn, help control the pests feeding on your onions:

    • Carrots. The smell of the carrot deters the onion fly

    • Catnip. While it won’t keep the cat away, it will keep beetles and aphids away from your onions

    • Marigolds. The smell of the plant repels beetles, flies, aphids, and other pests. The roots of the flower keep nematodes away. French marigolds are best at pest repelling

    • Peppers. Plant these next to your onions to deter aphids and beetles

    • Parsley and mint. Bugs can’t stand the smell of these two herbs, which just can’t seem to be killed. Good news for your onions.