Oleander Aphids and You
By Timothy Newcomb, Anoka County Extension Master Gardener Intern
Many of us have heeded the call to save monarch butterflies by planting milkweed in our home landscapes, and we’ve all enjoyed watching the baby caterpillars munching away happily. What we didn’t expect to witness, however, were the swarms of bright yellow-orange insects that moved in shortly afterwards. This army of small, soft-bodied vampires that appear poised to suck the life force from our monarch buffets are called oleander aphids.
The oleander aphid is named after its ideal food source, the oleander flower. Since Minnesota is too chilly for oleander plants to grow here, oleander aphids substitute milkweed, which is in the same plant family. According to the University of Minnesota Extension Service, oleander aphids are mostly harmless and rarely cause significant damage to milkweed. However, with a large invasion of oleander aphids, milkweed leaves may become shiny due to the excretion of honeydew, which can encourage the growth of sooty mold.
If your milkweed is playing host to oleander aphids, you might not get much help from nature in managing them. Oleander aphids carry cardenolide toxins from the milkweed they consume, and this makes them toxic to most predators other than the parasitic wasp. The best way to control oleander aphids is to plant the right milkweed for your landscape and keep it well watered. This will help your milkweed stay stronger and better able to handle the presence of oleander aphids. Do not fertilize your milkweed, as aphids will reproduce faster on plants with higher concentrations of nitrogen.
If aphids persist on your milkweed, there are more aggressive things you can do to help control these uninvited guests. The best method of attack is to manually remove the aphids. It sounds tedious, but it’s the only way to ensure you don’t accidentally kill a caterpillar. Insecticides will kill both indiscriminately, but your fingers can tell the difference. Squishing them with your gloved fingers is best, or if this makes you squeamish, another option is to rub them with a cotton swab soaked in rubbing alcohol. Aphids prefer tender new leaves, which grow from the tip of each stem, so concentrate your efforts there. If you have children around, perhaps you can make a game of bug hunting and let them do the work. Just don’t pay them by the bug, or you will go broke before they run out of aphids!
If a section of your plant is coated with aphids, you can trim off the affected area and dispose of it after checking for any caterpillars that would need to be relocated. If you have an out-of-control situation that won’t be remedied by trimming, you can also spray the plant with a hose, again checking for caterpillars that could also be displaced.
While a massive swarm of oleander aphids might look shocking, you shouldn’t let the threat of them prevent you from planting milkweed. The benefits of the milkweed to our pollinators greatly exceeds the nuisance value of this pest.
Save the date for the Home Landscape and Garden Fair on April 2, 2022 at Bunker Hills Activities Center in Andover, MN. For event registration and information about Anoka County Master Gardener projects and services, visit anokamastergardeners.org