10 Good Ideas for Keeping Milkweed Aphid-free…and 1 Bad One!
The degree to which their infestations effect plant health is debatable, but the ugliness they unleash upon your butterfly garden is not!
In 2011, they showed up in droves on our tropical milkweed. I cringed every time I walked by those plants and wondered if I should replace the tropical milkweed to cut down their numbers?
A couple gardeners assured me the milkweed would be OK. Miraculously, I even found two 5th instar caterpillars crawling over the orange-covered leaves!
However, the seeds I collected that season gave me a better indicator of milkweed health…only 20% of those seeds sprouted the next season! Every other year without heavy aphid infestations, seed viability has been about 90%.
Keep in mind expectant monarch mothers will also avoid laying eggs on aphid-infested milkweed leaves…and if they did, would you ever be able to find them?
Little did I realize, I could have stopped our infestation from getting so out of control. Over the years I’ve learned more about treating aphids and preventing infestations, so I’m here to help you avoid our aphid-blanketed milkweed debacle of 2011.
Of all the questions I receive about butterfly gardening, “how can I control aphids on my milkweed?” is probably the most frequent. A good idea for all gardeners is to check your plants regularly. Below, you might see two harmless aphids sitting under tropical milkweed flowers…
…but I see the potential beginnings of an aphid army!
Here’s are 8 tips to keep that aphid army from ever forming, so you can save your precious milkweed plants for monarchs:
1. RUB THEM OUT: some people simply get rid of aphids by rubbing them off with their fingers and thumbs . This can be effective when the numbers are low if you’re not afraid to get your hands (or gloves) dirty.
2. HOSE THEM DOWN: a steady stream of water on the aphids can also displace them. You’ll need to hold the milkweed plant with your other hand to avoid stem breakage. Using a spray bottle on stream is also effective.
3. ALCOHOL OVERDOSE: This was reported in the LA Times as the secret to killing milkweed aphids and not monarch eggs
Please note that if isopropyl alcohol is applied directly to monarch eggs or caterpillars it will kill them.
UPDATE: Community Member Joe G. says he uses a small spray bottle filled with isopropyl alcohol to spray the aphids on his plants. After about 5 seconds, he hoses the plant down with water and those pesky milkweed invaders are dead. This sounds like a great idea, but I would only recommend this for heavy infestations…don’t destroy your local ecosystem with an aphid-free garden!
4. WASH THEIR MOUTHS OUT: a little soap never hurt anybody, but it can kill those pesky aphids. Add 2 Tablespoons of dish soap to 1 gallon of water and spray the aphids directly, rinse, and repeat. Get more details here:
5. BRUSH THEM ASIDE: Use a detail brush to brush them off the milkweed plants and get in those nooks and crannies without damaging the plants:
6. DIVERSIFY and SCRAMBLE: This preventative measure can become very effective as your milkweed patches start to mature. Try planting several species of milkweed, and put them in several areas of your yard and garden. The aphids will likely have a favorite area and you can sacrifice one small patch to the angry aphid gods.
More milkweed varieties could attract more aphid predators too. Could it also attract more monarch predators? Yes, but that’s a good excuse to bring a few eggs/caterpillars inside to watch the amazing process of monarch metamorphosis.
Still have aphids? You have a couple options left to regain aphid control. Unfortunately, this next option option is unpredictable and could have unintended consequences…
7. WHO’S BUGGING WHO NOW?!: Introducing beneficial insects to eat the aphids sounds like a great natural solution, but beneficial bugs like ladybugs and mantids also feed on monarch eggs and larvae.
In some regions, parasitic wasps have been released to control unwanted pests. Unfortunately, these wasps are also targeting beneficial species, including monarchs! 🐛
There are already enough monarch predators in your garden…what will happen if you unleash thousands more?
8. REPEL WITH PLANTS: Some plants, including onions and marigolds, have been shown to repel aphids and naturally reduce their numbers. Planting these repellents close to milkweed can attract more butterflies while keeping aphid numbers down to reasonable levels.
California Butterfly Lady, Monika Moore, takes thin strips of banana peels and places them on milkweed stems near buds/blooms where aphids like to congregate…not appealing to aphids!
9. CUT IT OUT: If it’s come to the point where aphids have completely engulfed your milkweed, cut back all areas of moderate to heavy infestation and throw out. Make sure to discard the cuttings far away from the garden to avoid a touching aphid-family reunion. I suggest using a yard waste can if you have one.
Then, try options #2 , #3, or #4 on less crowded areas so they can’t start another infestation.
It’s not fully understood if/how oleander aphids overwinter, but cutting back infested milkweed plants in late summer/early fall might help you avoid an aphid Gardageddon next season!
How effective is this strategy? Video doesn’t lie:
11. A BAD IDEA: You could also apply a professional grade pesticide like
malathion, but it’s likely that monarchs, other wildlife, and the environment could suffer injury (or worse) from using harsh chemicals. There’s a reason butterfly gardeners use organic pest control…it won’t kill the butterflies!
Whatever solution you choose to control aphids, remember that early intervention is your best chance for for defeating these sap sucking pests.