You might be familiar with the butterfly gardener catchphrase plant it and they will come. The it I am referring to is, of course, milkweed…the lifeblood of monarchs!
Milkweed comes in many sizes, flower colors, and growth habits for North American Gardens.
The good news is that monarchs will utilize many different species of milkweed to support their life cycle.
The bad news is magnificent milkweed also attracts a variety of unwanted pests.
These pests can damage the milkweed so it’s less appealing (or unusable!) for the monarchs you are trying to attract and support.
In the long term, the best way to conquer milkweed pests is by diversifying your milkweed and by planting several patches around your yard and garden.
In the short term, a limited supply of milkweed might call for more drastic measures to take back your patch!
This is a (growing) list of all the usual suspects, and what you can do to save your milkweed for the monarchs:
Japanese Beetles
- Popilla japonica
- Common Milkweed pest and butterfly garden ornamentals including zinnias, butterfly bush
- Devastating damage to many tree/plant leaves and flowers included in urban landscapes
- Stop them from taking over milkweed by dropping them into a bucket of soapy water
- Pheromone traps work well, but keep them away from your garden to avoid attracting even more of these uninvited pests.
- Treat the feeding grubs in late summer/early fall by spreading the natural-occurring bacterium milky spore across yard and garden with a broadcast spreader
Beetles Be Gone! This tip was given to me by Lloyd Brace, who ran a rose nursery in Maine: “For bad Japanese beetle infestations, put a an inch or two of water in the bottom of a wet/dry shop vac. Add a little Dawn dish soap and stir. Go out in the garden and suck those suckers up. WARNING: It’s addictive. Once you’ve cleaned up your yard, you’ll want to go vacuum at the neighbor’s.” Go Lloyd!
Milkweed Beetles
- Tetraopes tetrophthalamus
- Often found on common milkweed
- Larva (grubs) burrow beneath the soil to feast on milkweed roots, which explains why you don’t see them crawling around your patch. They can also access the root by tunneling through the stem.
- These herbivores feast only on milkweed and won’t harm your caterpillars
- Squeaking? It’s been reported that milkweed beetles squeak excitedly when eating milkweed. if you’ve heard this squeaking please comment below…
- Leave them if you have enough milkweed to sustain them. They are harmless and part of you local ecosystem. If predators can’t find them, who’s left on your milkweed?!
- Stop them from taking over milkweed by squishing or dropping them into a bucket of soapy water
We never see large numbers of milkweed beetles in our northern garden…more proof that predators are adapting to the toxic cardenolides in milkweed.
Milkweed Bugs
- Oncopeltus fasciatus
- Female milkweed bugs can lay up to 2k eggs in one month
- Nymphs are mainly red with black markings
- Adults have full-grown wings
- Damage milkweed by eating milkweed seeds and tissue from the plants
- Protect your pods/seeds by tying mesh organza bags over them
- Stop them from taking over milkweed by dropping them into a bucket of soapy water
- Insecticidal soap is an option for heavy infestations- rinse plants thoroughly after use to protect future monarchs!
- They are omnivorous, focused mainly on milkweed, but will also eat eggs and small caterpillars
- Leave them if you have enough milkweed to sustain them. They are harmless and part of a healthy local ecosystem
Keep in mind, any substance left on milkweed to repel pests will also prevent monarchs from using those plants.
Milkweed Leaf Miners
- Liriomyza asclepiadis is the specific species of leaf miner that feeds on milkweed
- Small fly larvae that feed on milkweed in between leaf layers, making them unsuitable to nourish monarch caterpillars
- The only way to get rid of miners is by removing/discarding the affected leaves
- Systemic pesticides are used for large infestations, but this is not an option if you want to support monarchs
We recently had some leaf miner damage on our poke milkweed, and removing the leaves was effective in stopping their spread.
Milkweed Weevils
- Rhyssomatus lineaticollis is the specific species of milkweed weevil that feeds on common milkweed causing leaf damage and distortion
- R. lineaticollis feed on young common leaves before working their way to the stems to lay the foundation for the next generation
- Rhyssomatus annectans is the specific species of weevil that feeds on swamp milkweed
- R. annectans seem more stem-focused for feeding and egg laying. The less substantial swamp stems start to droop before breaking. These swamp milkweed buds will never bloom to support monarchs and other pollinators 😞
- Since these nocturnal pests are milkweed species specific, some have suggested crop rotation. However, since these are perennials, that doesn’t seem feasible
- IF weevil damage is a serious issue in your region and you want to prevent this from occurring, get out that soapy bucket of water in spring (hopefully before weevil eggs are deposited) and start flicking them in. Otherwise, weev them be 😉
In our northern region we haven’t found weevils to be a serious issue on common milkweed, but they are wiping out too many stalks of swamp milkweed. Next spring, they will be dealt with…
Oleander Aphids
Oleander aphids (Aphis nerii) are probably the grand daddy milkweed pest of them all. While many of the pests on this page are regional, aphids have become equal opportunists across North American butterfly gardens.
In fact, as a special pest of honor, they even have their own page:
10 Ways to Stop Aphids from Taking Over your Milkweed Patch
Snails and Slugs
In our northern garden, these are not an issue, but some gardeners in warmer regions rank these as their worst milkweed pests. They sneak in at night and leave you with a sorry milkweed patch surprise the next morning.
After researching the topic, I came across a few different solutions including epsom salt (hydrated magnesium sulfate) which is also beneficial to plants. If you use epsom salt, keep in mind this has the same potential issue for caterpillars as spreading diatomaceous earth…when the caterpillars crawl off the milkweed, sharp crystals can cut them open and kill them.
If you water the epsom salt areas thoroughly before caterpillars cross the soil to pupate, this can be an effective solution:
Regular snail baits are toxic to other animals and wildlife including your pets, so I would think twice before using them…
With Sluggo Organic Snail Baits, the iron phosphate and bait combination immediately stops slugs and snails from feeding after the bait is eaten. The pests will die within a few days…
Sluggo is non-toxic to pets and other wildlife:
Buy Sluggo Organic Snail Baits here
Spider Mites
What can you do, when you first start noticing spider mites on your milkweed?
- Tetranychus urticae
- Hope their natural predators (including lacewing larvae) will take care of them for you
- Cut back affected areas and discard…don’t compost!
- Rinse spider mites away with water. I’ve heard from many gardeners this isn’t very effective
- Isopropyl alcohol will kill them on contact. Apply with a spray bottle or cotton swab.
- Insecticidal soap works too. You can even make your own at home
If your plant looks like the video above, it’s time to cut your losses and hope for a fresh start next season. Early intervention is the key…
Swamp Milkweed Leaf Beetle
- Labidomera clivicollis
- These have become a major issue in warmer regions decimating milkweed patches, and stopping them from flowering/seeding
- Don’t be fooled by their common name…they’ll eat many types of milkweed
- in northern regions they are less of an issue because they show up later in the growing season so there’s only one generation
- Reduce their numbers by flicking them into a bucket of soapy water OR
- Remove eggs you find on milkweed or nearby plants, but don’t confuse them with beneficial ladybug eggs
In our northern garden, we only remove Labidomera eggs, but don’t go out of our way to look for them. They have not proven to be a serious pest…yet.
Thrips
- Thysanoptera order
- Nicknamed freckle bugs because of the white-freckled damage that occurs on the plants.
- Long, slender insects with fringed wings
- Adult thrips are about 1mm (.04 inches) long
- Over 6k recorded thrip species that suck the life from plants around the world, including your precious milkweed 😱
- Thrip damage ruins leaves, milkweed flowers, and negatively impacts seed viability.
- Look for leaf streaks, speckled leaves, and small white patches. See actual thrip damage here
- Ladybugs and lacewings are natural thrip predators
- Spray affected areas of plant with water to get them off OR
- Cut off affected areas of plant and discard OR
- Use insecticidal soap (rinse plants thoroughly after use). You can even make your own at home
- Do not use neem oil or other systemic pesticides that will kill caterpillars.
Tussock Moth Caterpillars
- Euchaetes egle
- Often found on common milkweed, but they feed on most varieties
- Nicknamed the tiger milkweed moth for its orange, black, and white hair tufts
- While they can decimate milkweed, their numbers are kept down by predators.
- Adult moth has gray wings and a yellow abdomen with black spots
- Leave them if you have enough milkweed to sustain them. They are harmless and part of you local ecosystem. If predators can’t find them, who’s left on your milkweed?!
- Stop them from taking over monarch-reserved milkweed by relocating eggs/small caterpillars to older milkweed plants. Dogbane is an alternative tussock host.
Whiteflies
- Trialeurodes vaporariorum
- Whitefly is a common pest in western states
- Hurts milkweed by sucking sap from leaves
- Stop them by spraying leaves with water or using an insecticidal soap
- Spray isopropyl alcohol on eggs and/or flies…this has worked well on our overwintering plants
- Blow on them and they’ll fly away…but will likely return when the coast is clear
- Vacuum them up with a micro vacuum attachment or a mini keyboard vacuum cleaner
Question to Consider: if a milkweed pest isn’t causing serious damage in your region and your milkweed patch, it is really a pest?
More Milkweed Pests Coming Soon…😱
