Aphids Q&A

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By Sandy Swegel

We got a great question from a customer this week about controlling aphids. Her frustration resonates with most of us who garden.

Q. Aphids are terrible, tiny creatures and I fight them every year. I’ve been looking for the best ways to make sure they don’t screw with my garden this time. I thought I had a good way; planting garlic around the plants. “Aphids don’t like garlic,” one link said.  “Aphids love garlic leaves, said another one. Soap mixture, Neem oil, rubbing alcohol mixed with soap and water, importing good bugs that love to eat the aphids. I refuse to use chemicals that poison everything, it makes growing organic pretty pointless. Does anyone have any SURE FIRE, tried, and true methods?

A. The key to reducing aphids in your garden is to understand their lifestyle. Controlling them is like cleaning the house. You can’t just clean a house full of people once and expect the house to still be clean a week later if you didn’t keep picking up stuff all week. When you use any treatment you might kill most of the adult aphids that day. But the ones you missed or who were eggs that wouldn’t hatch for another day, are still eating and reproducing. Reproduction is the key to aphid success. They reproduce both sexually and asexually. They lay eggs to survive the winter. And they have live births in warm weather. Each one can create up to 100 new aphids per month.

My best sure-fire, tried and true method (or as close to that as one can get) is this:

Accept that you are going to have some aphids. To kill them all, even if possible, means you would also kill all the beneficial insect pollinators and you don’t want to do this.

Understand how aphids die. Warning: graphic content ahead.
It is super easy to kill aphids, which is why plain water spray works great. Aphids feed by attaching to the plant with their mouths. When you spray water on the aphids, the force of the water tears the aphid off the plant. The head and mouthparts stay attached to the plant, instantly killing the aphid. Even just brushing off all the aphids on a leaf with your finger decapitates and kills all those aphids. That’s why you don’t have to poison them…if you can just mechanically remove them.

Be vigilant (every few days) about checking for aphids.
New aphids are hatching in leaf litter or being birthed by the aphids who were hiding out in the weeds next door. You have to spray the aphids every time you see them in large numbers. Each aphid can have dozens of generations…They are baby-making machines. You have to keep after them at least until you see you are no longer getting infestations.

Be careful not to eliminate beneficial insects.  There’s yet another reason not to try to kill off aphids outside, even with “safe” organic treatments like soapy water. If you kill the aphids, the aphid-eating wasps, another of those native beneficial insects, won’t have anything to eat and they’ll leave your garden.  They are eaten by so many beneficial insects that it’s rather amazing that we see any at all. Yet there are so many on our plants at times.

This week I’m seeing thousands of them on the new growth of roses. And while my first instinct is to kill them in some way, I have finally learned to just watch them. I know what I am seeing is a mini-population explosion that will usually be followed in a week or so by mini-population explosions of predators that eat aphids. If we try to kill off the aphids which are at the bottom of the beneficial insect food chain, then the beneficials will fly away to another garden.

I knew about many of the predators of aphids like ladybugs and lacewings, but I learned yesterday that tiny native aphid-eating wasps eat a LOT of them. In addition to wasps that just eat the aphids, there are parasitic wasps that lay their eggs inside of them. When the eggs hatch the tiny larvae eat their way out of the aphid. A bit gory, but effective in guaranteeing enough food for baby wasps.

So I challenge you to a two-week experiment. Let the aphids be when they show up and just watch the plants for a few days. See who shows up to dine on them. Some possibilities include wasps, both large and small, hoverflies, ladybugs, and lacewings. It will be a fascinating discovery of how many small beings live in your garden, there to help you keep everything in balance.
Nature does provide a natural balance if you have a healthy garden that supports beneficial insects. If you are aggressively treating aphids with garlic or neem sprays, you are also killing all the other insects that eat aphids.

Alter the conditions in your garden that reduce the number of aphids.

Don’t over-fertilize. Aphids love nitrogen. You will get a little aphid bloom every time you add nitrogen to your plants. Reduce the nitrogen and you don’t have so many of them.

Encourage earthworms and use earthworm castings. Earthworms produce an enzyme chitinase to help digest their food. Aphids are repelled by chitinase. Unfortunately, the chitinase doesn’t last long enough to be the only deterrent.

Encourage good environmental conditions like airflow and temperature. This works really well indoors. In my greenhouse, I can reduce aphids by keeping a fan going and shading the plants from the really hot afternoon sun. They are often in greater numbers on plants that are stressed.

Finally, if you do want to use “organic” sprays, simple soapy water works well. (1 teaspoon per gallon). Some people use the kitchen spray with garlic and Tabasco sauce. I think the science is not clear on neem. It definitely works but it works by disrupting insects’ hormonal systems and I’m not convinced it doesn’t adversely affect beneficial insects. Some studies say Neem only kills sucking insects. I would try gentler methods first before turning to Neem.

More about gardening and aphid control

More about interactions between predators of aphids

Photo credits:
https://en.wikipedia.org/wiki/Aphid