As you plant and cultivate milkweed, you’ll find that there are some common problems. A healthy supply of milkweed leaves is important for both attracting monarchs and for raising them indoors.
Common milkweed leaf problems include pests (like aphids, beetles, and milkweed bugs), powdery mildew, leaf spots (fungal and bacterial), rust, and cucumber mosaic virus. Some of these are easily treated, and others require more effort. Here’s how to identify the milkweed leaf problem and fix it.
Milkweed Leaf Problems
There are certain problems that you may find when you have milkweed (Asclepias) and they are probably similar to most of the plants in your garden.
Many are caused by fungi and some are caused by bacteria. Others are from pests.
Here are the common problems you might face when growing milkweed at home.
Bugs and Insects That Harm Milkweed
Other problems are caused by milkweed pests, like insects and bugs. These pests eat leaves, seeds, and stems, and suck sap from the plant.
Some harmful insects include:
- Butterflies and moths (especially in their larvae stage)
- Leaf miner flies
- Milkweed bugs (both types)
- Milkweed aphids
- Beetles (red milkweed beetle, Japanese beetle, milkweed stem weevil)
Here’s more about common milkweed pests.
Powdery White Mildew (Foggy Mornings)
Powdery mildew is a white, powdery-like spore. Avoid feeding your monarch caterpillar leaves with mildew.
There are two causes of powdery mildew.
- It can occur when the leaves are wet for an extended period.
- It can also occur if humidity is high but dry then you can end up with powdery mildew on the leaves.
How can a climate be humid but dry? Well, if you have fog in the morning and then sunshine later in the day, it is ‘humid but dry.’
To help the plant, you can remove the leaves carefully. And water during the day when the leaves will be able to dry. Unfortunately, there’s nothing that can be done about the fog!
Here’s how to treat powdery white mildew in the garden.
Milkweed Leaf Spots: Fungi and Bacteria
If your leaves start to get spotted then you may have fungal leaf spots. This can be caused by a variety of fungi and usually happens when conditions are wet.
It can also be a bacterial leaf spot which is definitely a potential problem for monarchs.
This can be caused when plants are water-soaked irregularly.
A way to avoid this is by avoiding overhead watering of plants, particularly in the evening. And increase the airflow to promote drying of the milkweed leaves.
Be sure to remove all leaves that appear diseased. And don’t use them as food for your caterpillars! And pick up any milkweed leaves that have fallen off.
Rust causes the milkweed plant to end up with yellowed leaves and end up stunted in growth.
It also causes reddish-colored spots on the leaves. Remove the leaves carefully so as not to scatter the fungal spores.
Cucumber Mosaic Virus (CMV)
There is a virus called the Cucumber Mosaic Virus (CMV) that causes plant foliage to ‘crinkle up’ and also stunts plant growth.
This can attack milkweed but also mimics other types of damage (spider mite damage, for example).
Spider mites are aggressive arachnids that will harm your milkweed plant. Like the oleander aphid, they are sap-suckers that will deform your leaves.
If your leaves are crinkling, don’t assume that you have Cucumber Mosaic Virus.
- First, you should turn your leaves over and check for white webbing and little spots. Using a magnifying lens, inspect the spots.
- You can also tap the leaf against a white sheet of paper and if any little dark spots appear, you probably have mites!
How to Control and Prevent Spider Mites
Here’s a great tutorial by Epic Gardening about how to identify, control, and prevent spider mites in the garden.
To reduce the spider mite population, spray the undersides of the leaves with a hard spray of water, as you would to remove aphids.
Keeping the dust in the area down (spraying the area with a mist of water) can also help.
The use of pesticides or miticides is not recommended as 1) many become resistant and 2) these can harm/endanger your butterflies!
As with other leaf problems, pluck off the leaves and dispose of them. Leaves may curl and can become spotted and discolored from mite damage. Watch for a blonding of the green color.
If you notice these changes remove the leaves and throw them in an enclosed compost bin or the trash.
Be sure to wash your hands carefully before handling any butterfly eggs, larvae, or adults, and remember to only use healthy-looking foliage when feeding your caterpillars!
Feeding your larvae diseased milkweed leaves may make them sick. Remember that poor food quality will cause health problems in your butterflies.
What type of milkweed leaf problems have you faced? Have one to add? Or maybe a solution? I would love to hear from you.
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Bryan Haines is a co-founder and writer at The Buginator. And is working to make it the best resource for taking back the outdoors from biting, stinging pests.
He also blogs about travel at Storyteller.Travel and photography at Storyteller Tech. Bryan is a partner at Storyteller Media, a publishing company he runs with his wife, Dena.
Sunday 9th of April 2023
Hello, I have around 50 various species of milkweed plants and they all are getting infected with rust. I have tried the peroxide spray and and soap and it isn't helping. Any thoughts. Also, can the Monarch caterpillars eat leaves with rust? Thanks so much.