Milkweed problems

Milkweeds are pretty easy to grow, but we watch out for the following things.

Spring: Don't think it's dead

Milkweed in spring ©Janet AllenMilkweed in spring

Milkweed doesn't start growing as early as other plants in the spring. The first year we grew it, we thought it hadn't made it through the winter. Not so! It generally survives the winter quite well—it's just a little lazy coming up.

This photo was taken on May 8, a time when many other plants were already up and had been growing for a while.

We leave at least some of the previous year's stalk (as seen in the photo) throughout the winter as a marker so we know where it should be coming up in the spring.

A bonus of leaving the stalks is that I've seen its hollow stem used by birds as a place to cache seeds. I've also seen birds stripping the fibers off the stalk in the spring to use as a nesting material.

Milkweed herbivore: Aphids

Aphids on milkweed ©Janet Allen Aphids on milkweed

By the end of the season, we end up with oleander aphids on our milkweeds. (Oleander aphids are non-native, introduced from the Mediterranean region.) They don't seem to be a problem earlier in the season.

When I'm cutting milkweed to bring inside for our caterpillars, my hands can end up orange—yuck!—but seeing my beautiful orange monarchs later emerge is a good enough trade-off! I guess I could wear gloves, but I've never liked to garden in gloves. A quick hand-washing is easier for me.

One way to get rid of the aphids is to put on gloves and rub your hands along the aphid-covered stems.

Some people blast plants with water as a non-toxic way of ridding plants of aphids—BUT I wouldn't want to do that on milkweeds. There could be tiny monarch caterpillars blasted away with the aphids!

Something I plan to try: interplanting my milkweeds with basil since aphids are supposedly repelled by its smell. Some websites, though, indicate that basil attracts aphids. The only way to find out is to experiment with a patch and see.

Milkweed herbivore and predator: Small milkweed bug

Small milkweed bug ©Janet Allen
Small milkweed bug

The preferred food of the small milkweed bug (Lygaeus kalmii)? Milkweed seeds! This is bad enough, but they also eat caterpillars or even the chrysalides. We have quite a few of these. They haven't been too much of a problem, though, since I collect the monarch eggs to raise inside, and I have enough seeds even if they eat some.

In the world beyond my yard, though, they could present a problem I would think.

Milkweed herbivore: Tussock moth

Eggs of tussock moth ©Janet Allen
Eggs of tussock moth

I found this odd thing on the bottom of one of my common milkweed plants.

First instar of tussock moth ©Janet Allen
First instar caterpillars of the tussock moth on common milkweed

On another leaf, I saw this mass of little caterpillars. I sent the photos to In just a few hours, I got the answer: the first instar of tussock moth caterpillars. The white structure in the photo above is the bunch of eggs.

Then I remembered that I had seen tussock moth caterpillars on my milkweeds before.

Tussock moth ©Janet Allen
The tussock moth caterpillar — an amazing looking caterpillar

What to do with this native caterpillar? I've generally left single large tussock caterpillars even though they eat the leaves, but I keep my eye on them.

I removed the egg mass and the mass of first instar caterpillars, though, since there were so many of them. They can defoliate the milkweed and they happened to be on the common milkweed plants where monarchs had been laying eggs.

Milkweed herbivore: Swamp milkweed beetle

Milkweed beetle ©Janet AllenMilkweed beetle eating my swamp milkweed

In our yard, the swamp milkweed beetle has been the major problem.

We've been seeing many more swamp milkweed beetles the last few years. They've been eating my milkweed as soon as it emerges.

Usually I try to live and let live, assuming that some predator will arrive to take advantage of any insect surplus, but these were more than I could deal with.

Eggs ©Janet Allen
The eggs

We collected many (not all) of these beetle and larva and dropped them in soapy water. I was very conflicted about this, but decided that in this case, I had to come down on the side of growing more milkweeds. My decision was affirmed when I asked an entomologist about this quandry at the Millersville Native Plants in the Landscape conference.

I find clusters of these orange eggs on the bottom of the swamp milkweed leaves.

Larvae ©Janet Allen
Larvae and eggshells

Here they've just hatched. Note the veins of the leaf to get an idea of their size—pretty small.

Milkweed beetle larva ©Janet AllenMilkweed beetle larva

This is the larva of the milkweed beetle (Labidomera clivicollis) that was eating so many of our plants.

What to do? I try to make these difficult decisions in the context of how people have destroyed the balance of nature in so many ways. In our highly artificial suburban environment, are the number of milkweed beetles and their predators necessarily going to be in harmony anyway?

However, I still feel uncomfortable about this—in contrast to how I feel about doing the same thing to the non-native Japanese beetle.

Milkweed Yellows (Phytoplasma)

Milkweed yellows ©Janet Allen
Milkweed yellows (Ahk!!)

I was alarmed one year when I started having strange-looking milkweeds. Fortunately, I asked an expert about it and he said he was afraid I had "milkweed yellows" or phytoplasma to be more technical. He said it was spread by leafhoppers from plant to plant.

This was very depressing to say the least. I finally had the courage to pull out the affected plants (a lot of them), stuff them into a black trash bag, and discard in them in the trash.

The following year, I still had to monitor my yard closely and pull up any that looked the least bit strange. But the good news is that I think I caught it fast enough and now my milkweeds look fine.

Just as alarming, on one of our Wild Ones chapter field trips, we found this problem in a few places in an otherwise wonderful monarch breeding area. The steward of the property said he'd removed all the infected milkweeds. I hope he caught it soon enough!

If you think you may have this problem, check out the MonarchLab info on this to be sure you're diagnosing the problem correctly.


Herbicided milkweed ©Janet Allen
Milkweed in the local mall's parking lot killed by herbicide

Of course, herbicides will kill any plant. The problem for milkweed is that it's often growing in places where highway departments or maintenance people are used to thinking of it as a "weed" and used to eradicating it. Spraying herbicide is a quick way to make roadsides look "neat."

I can only hope that there were no eggs or caterpillars on the milkweed when it was sprayed.