Aphids are the only garden pest that regularly give me recurring nightmares. They're not the most destructive of garden plagues, but nevertheless, I hate them. I hate how they move, I hate how they reproduce, and I especially hate how their population levels can sneak up on you out of nowhere.
I have to admit, aphids are remarkable from an evolutionary perspective. They have a highly successful and complicated reproductive system. To boil it down to what we need to know as gardeners, aphids reproduce asexually and give birth to live young, so their population can go from negligible to crisis seemingly overnight. One female aphid that emerges in the spring will give birth to thousands of descendants over dozens of generations.
Did you know they also live symbiotically with ants? Ants actually raise them like little tiny cattle in order to extract a sticky substance that aphids secrete. Aphids are bizarre, resilient creatures.
Because we didn't get an extended cold period here in Memphis this winter, they're back early and with a vengeance. They've already colonized all of my kale plants and some of the radishes, too. Aphids feed on garden plants by puncturing holes in the leaf surfaces with their mouths and sucking all of the fluid out. As a double whammy, like any piercing-sucking insect, they're vectors for disease. I've watched a small aphid infestation take out an entire greenhouse operation by transmitting Tobacco Mosaic Virus from one suspected plant.
Aphids like to hide on the underside of leaves, especially pushed up next to leaf veins. Most aphids are slow-moving six-legged wingless creatures. However, their confoundingly frustrating adaptive genius lets them know when their population levels are getting too high for a plant, and when that happens, they have babies with wings, so they can fly off in search of new crops to destroy.
So what do you do about them? Well in low numbers, nothing. (Except to squish them out of cold-hearted fun.) Low numbers of aphids don't cause much harm. But the trick with the sustainable management of any garden pest is to not allow for population explosion.
I'm slightly neurotic when it comes to garden pests. I scout for insects at minimum twice per week. That means that in every single one of my raised beds, I turn over four or five leaves in different locations looking for signs of harmful insects or insect damage. With aphids in particular, I look for ants running up and down the stems of my plants, because there's a good chance that they're harboring aphids.
If I see aphids, I squish them immediately. If I see lots of aphids, I'll rip the whole leaf off and stomp on it while cussing colorfully. (It helps, promise.) Sometimes, though, there are too many to pick or stomp. If that's the case, I spray the plants with neem oil. Neem oil is botanical; it's pressed from the neem tree. It works basically by making the aphids forget to eat and mate. I purchase a concentrate and dilute it to label specifications in my two gallon sprayer. With bad infestations, I wait a week and follow up with a concentrated pyrethrum spray, again buying in concentrate and diluting.
While both pyrethrum and neem are derived from plants and generally considered safe, I take as many precautions as I can. I did not use either of those products when I was pregnant. We had one bad aphid and flea beetle outbreak during my pregnancy, and my husband sprayed pyrethrum and neem twice each. I also waited a couple of days before handling the plants after that. I wear chemical-grade neoprene gloves and a rubber jacket that I only use when spraying for insects. This might seem like overkill, but I am of the mind that I'd rather be safe than sorry. Putting on gloves and a jacket takes me an extra thirty seconds, and I'd like to have that peace of mind. I also never spray if it's windy.
As I said, aphids are adaptive geniuses, and they can quickly build up tolerances for pesticides, so whatever your pest management plan is, it's important to keep it as varied as possible.
There are ways to manage infestations that don't use any chemicals at all. If you have an aphid outbreak in a greenhouse or under a low tunnel, I have found that purchasing ladybugs and releasing them is a great solution. It's trickier to use this technique in open areas, because ladybugs will often just fly away. If you decide to go this route, I recommend watering in the late afternoon so that there are little pools of water available to the ladybugs to drink, then releasing them in the evening. If they have food and water sources, they're more likely to stick around if they wake up in your desired location. Also, I know this is obvious, but you don't want to release ladybugs if you are also using pyrethrum or neem.
You can also make soap sprays. Now, I don't care what you saw on Pinterest, but please do not make soap sprays out of Dawn dish soap! Detergent-based soaps will strip the protective coating from the leaves of your plants. I have used a diluted Dr. Bronner's Peppermint Oil Soap spray before. It can suffocate the aphids when the soapy water is sprayed directly onto their skin. It is really only effective for smaller infestations in smaller areas, but it can be a helpful method to use in combination with other techniques.
I hope your aphids stay away from your garden as long as possible this year. Do you have other aphid management techniques that you like to use? Drop your advice in the comments.