What to do about aphids
Aphids are a notorious pest to the native plant garden – specifically the little yellow oleander aphids that can quickly overwhelm and cover an entire milkweed plant. Many of the insects found in a native garden are part of a natural food web and a sign of a healthy ecosystem. But aphids are just a big bummer: they are gross and they can ruin your milkweed before any monarchs get the chance to move in.
So what can you do about aphids?
Here’s what we do:
Squish them as soon as we see them! Female aphids are born already pregnant, so they can get to laying eggs right away, which leads to explosive population growth. Diligent monitoring is a proactive approach to controlling aphid infestations.
When a plant is totally covered, we’ll squish them then too. Personally, I find it a little icky, but I’ve had friends who have used wet dish towels to squish and wipe their plants clean. What I do instead is cover the aphids with soapy foam. Soap is an effective insecticide, and the easiest way that I’ve found to apply it is to apply soap suds directly to the aphids. I’ll usually take a wide mouth cup – like an old yogurt container– put a few drops of dish soap in the bottom, and then turn the shower nozzle of the sink on full blast. This usually churns up some decent soap suds that I’ll apply to the aphids using my fingers. The soap has to come into contact with the aphids to work. Keep at it a few times a week to get the population under control.
We’ve also cut plants down to remove infestations. Milkweed is pretty hardy and will happily grow back after being chopped. When we have removed the infected plant parts, we’ll dunk them in soapy water to kill the aphids, and then will put the plant in the trash.
Safe Soap Use
The soap can inadvertently kill monarch caterpillars, so make sure you don’t have any caterpillars on your milkweed before you apply any soap. You should also look out for any aphid eating predators! (Always watch out for your predators!) The safest thing to do for the caterpillars is to time your soap treatments outside of the migration time windows – which are mid April and late summer (late august through September). Additionally, you can rinse off the milkweed a day after the treatment to remove any soap residue. If a milkweed leaf on an infected plant has an egg on it, remove the entire leaf with the egg and manually kill any aphids. You can then hatch the egg in your own butterfly habitat, or put it on another plant.
Other Ideas, sourced from ‘round the web:
Buy ladybugs and or lacewing larvae. The purchase of lady bugs can be controversial: many are nonnative, and the ones that are tend to be unsustainably harvested from the Sierra Nevadas. Lacewing larvae, on the other hand, are grown in a lab, and are therefore a more sustainable choice. Renfrow’s Hardware store in Matthews sometimes has lacewing larvae for sale.
Apply diatomaceous earth on the soil. Since aphids come up from the soil, diatomaceous earth can kill them before they get to the plant. This only works if you apply DE before the aphids emerge so it is not effective if they are already on your plant. Additionally, DE needs to be reapplied after every rain, and some folks don’t like the dust (although some forms of DE are safer than others).
Reduce excess nitrogen. This article has a great explainer on the relationship between aphids and nitrogen. The main gist of it is that aphids like nitrogen, so having too much nitrogen in your soil will attract aphids. Replacing chemical fertilizers with compost, as well as getting a soil analysis can help you mitigate excess nitrogen. An interesting tidbit noted in the article: a study found that naturally produced nitrogen was associated with lower aphid populations. This makes me think that co-planting legumes (like baptisia or partridge pea) around your milkweed could improve the soil chemistry and maybe lead to fewer aphids. We’ll experiment and report back!
Natural Predators
When it comes to insects with agility and fitness, aphids ain’t it. That, and their plentiful numbers, make them a great food source for other insects. In our garden, I’ve seen aphids get eaten by lacewing larvae, hoverfly larvae, and earwigs. There are also certain wasps that parasitize aphids, and praying mantises will also eat aphids, although I’ve never witnessed either in our garden (maybe someday though – please grace us with your presence, Mr and Mrs Mantis*!). The best thing you can do to attract predators to your garden is to have a kick-ass and healthy ecosystem going on. And don’t spray insecticides outside. And if you’re going to use soap on an aphid-covered milkweed, make sure there aren’t any other insects or larva on it at the same time!
One insect that is very non-beneficial to the anti-aphid cause is the ant. Ants actually farm aphids, and will protect them from all the aforementioned predators. Ants like to eat aphids’ sugar poop (called honeydew 🤮). So watch out for ants around your milkweed and try to get rid of them (terro ant baits are relatively safe for other insects because they only attract insects that like sugar).
GOOD LUCK!
Aphids are not fun to deal with! If you can, try to be zen about it; they probably won’t kill your plant, so you can always just leave them be. But if you can’t stand it, try some of the techniques mentioned above. Let me know what works for you!
* Mantis side tangent: I was maaaaaaybe going to suggest getting familiar with what Praying mantis egg sacs look like, so that you can maaaaaaaybe kidnap one and raise your own army of garden protecting mantis super killers. (Please note that the formal policy of Bring Back the Butterflies is that we do not endorse the trafficking of any insects or wildlife – unless it’s a rat, and that was only that one time, and we didn’t take it very far!!!). That led me to this article, which has a handy chart showing the different types of mantids, and what their egg sacs look like. The article noted that mantids are ruthless, blood thirsty assassins that have such murderous skill that they can actually kill birds!!! They also pointed out that there are nonnative Chinese and European mantids that are bigger and much more murderous than the native Carolina mantis. The result is that those two big bois can outcompete the native mantids AND do a number on the native pollinators in your garden. The article advises that you should destroy any egg sacs for the Chinese or Europeans mantids that you come across, and leave the Carolina mantis egg sac alone! Sooo, don’t kidnap any mantis eggsacs (ootheca) and just let them come to you.
