Why is it important to control aphids on milkweed plants?
One of the most important and attractive butterfly lures you can add to your garden is milkweed.
The 200 plus members of the Asclepias genus are members of the dogbane (Apocynaceae) family. This plant group is toxic to humans but essential for monarch butterflies.
What makes this genus so important is that its members, such as butterfly weed are major sources of food for monarch caterpillars.
Monarch butterflies are one of the most iconic butterfly species. Monarch’s are part of a population report due for release in December 2020. This report may add them to the endangered list.
The concern for their status is due to a rapid decrease in overwintering populations. This despite the species having no shortage of breeding pairs – including the International Space Station.
Butterfly gardens are considered vital to the conservation of pollinators such as bees and butterflies. Butterfly gardens are included in the national preservation strategy of the Pollinator Task Force created in 2014 by President Obama.
Unfortunately, not everyone got the memo! The important milkweed plant (and indeed your entire butterfly garden) are prime targets for aphid attacks.
What Are Aphids?
Often referred to as garden vampires, aphids are a wide range of species that drink the sap of plants.
Some species of aphid are kept as cattle by ant colonies, who harvest their honeydew for food.
The most common aphid species found on milkweed is the orange Oleander aphid. This sap sucker has earned it the nickname of milkweed aphid.
What Damage Do The Milkweed Aphids Cause?
It might be difficult to see the damage aphids wreak upon your milkweed, as the plants themselves often appear healthy.
But, the evidence comes during propagation, with the percentage of viable seeds reduced by more than ¾.
Aphids produce honeydew, which leads to the development of sooty mold or other plant pathogens.
Aphids may also attract other pests which can do more obvious harm to your plants.
One of the scariest problems with aphids is that they are capable of telescopic generational reproduction.
This means that female aphids give live birth to their nymphs, which may already be pregnant without the intervention of a male.
Adults are also avid breeders, resulting in potentially devastating populations in a short period of time.
Not only do aphids drain the sap from plants, their honeydew can lead to the development of sooty mold.
How To Control The Milkweed Aphid
Your first instinct in tackling an aphid invasion may be to grab some commercial pesticide, but this is one of the worst possible solutions.
No pesticide is 100% percent effective, and will also kill beneficial insects, including the butterflies.
Additionally, aphids tend to feed on the underside of leaves where the veins are more exposed, shielding them from many pesticidal attacks.
Another method which may do more harm than good is attracting beneficial insects.
Ladybugs, mantids, and parasitic wasps are usually great for gardens, but have been known to snack on butterfly eggs and larvae.
Thankfully, there are many safer remedies that allow you to target the aphids specifically.
Here are just a few of the available options, both natural and chemical.
Natural Options
Spray bottles are one of the quickest ways to remove an aphid population.
Simply hold the milkweed plant in one hand and shoot the aphids with a spray bottle of water set on stream to knock them off.
Mixing two tablespoons of Dawn dish soap into a gallon of water will clog their breathing holes and make the spray lethal.
Just be careful not to spray any caterpillars when using a soap solution.
The value of complimentary gardening (mixing plants that benefit each other) can never be stressed enough.
Protect your milkweed by planting onions or marigolds nearby.
These plants not only repel aphids, they help attract butterflies, making this a win-win option!
Another, more hands-on approach is to gently rub infested leaves with your fingers, which will kill these pests.
Chemical Options
Unfortunately, there are no chemical options which are perfectly safe for both monarch adults and their larvae. But, there are two options which work well if you take care to temporarily remove any monarch caterpillars before using.
The most promising chemical option is pyriproxyfen. This chemical interrupts the molting process of nymphs, preventing them from achieving adulthood.
The chemical has mild to moderate toxicity in bee species. The effects can be kept minimal if the plant is sprayed early in the morning or late at night when pollinators are least active.
Avoid using this chemical if the plants are near hives, as the wind may cause particles to drift.
Another good option is pymetrozine. This chemical disrupts the feeding habit of certain insects, including aphids. Use this chemical either early in the morning or late at night.
There are no known effects on pollinators. Removing caterpillars during the process is strongly advised, as the full effects of this chemical on immature pollinators are not yet known.