Hello garden gals and guys!

Have you ever grown green beans and everything was going great and then one day you go out into your garden and they look like this:

Picture courtesy of N’Ckyola Green, Gardener

This is exactly what happened to one of my gardening buddies, N’Ckyola, and she had no idea what was going on.

But I did.

You may have heard me mention a few times that I completed the Maryland New Farmer Trainee program. I spent an entire year working on an organic farm. One of the many veggies they grew were beans. And some of their beans looked like the picture above.

I asked my farming mentor what caused it and he told me.

Mexican Bean Beetles.

What?

Then he searched around in the bean plants and found one and it looked like this:

I said “wait…that looks like a ladybug.”

Friends, that ain’t no ladybug.

What is a Mexican Bean Beetle?

Mexican bean beetles are the most common problem gardeners encounter when growing beans. Adults and larvae feed on the leaves and pods of all kinds of beans.

The adults overwinter in woods and weeds, making it hard to get rid of them once they get established. The females lay clusters of yellow eggs (more about that in a minute) on the undersides of leaves.

You’ll start to see them in your garden in mid to late spring, right when your beans are beginning to take off. The adults look like the picture above.

Okay, back to those eggs.

When you’re growing beans, it’s a good idea to occasionally turn the leaves over and inspect them. You might find little yellow eggs that look like this:

Those are the eggs of the Mexican bean beetle. They only take about one week to hatch. They are usually in clusters of about 40-75 eggs. See how easily this pest problem can get out of hand?

You might also find little buggers like this one eating away at your leaves:

That’s the Mexican bean beetle in its larval stage. You can see that it has eaten away at the flesh of the leaf in between the veins.

What Bean Beetle Damage Looks Like

Here are a few more pictures of the damage done to my gardening pal’s bean plants:

Now, this is just the beginning of them eating the leaves. If you don’t find these little buggers and get rid of them, your leaves can end up looking like this:

And eventually like this:

Left untreated, eventually they will strip your plants bare. And you’ll get no beans at all.

How to Treat Mexican Bean Beetle Damage

There are a few ways to get this pest problem under control.

Put your garden gloves on and squish any eggs you find. I know. Yuck. But finding the eggs and destroying them will keep these pests from getting out of control.
Handpick the larval and adult stage beetles and drop them into a bucket of warm, soapy water (or squish them, too, if you’re not squeamish). Remember, mated females can lay 40-75 eggs at a time. And these pests also overwinter. So handpicking is an important part of controlling the problem.
Plant lots of flowers with your beans to attract beneficial insects that are natural predators to the bean beetle. Also try planting beans in between rows of potatoes.
Install a floating row cover and open it regularly to check for beetles and remove any you find.
Clean your garden at the end of the growing season. Getting rid of infected plants reduces the chances of insects overwintering in your garden.

The steps above are good enough for the average backyard gardener.

If you’re on a huge farm, then you might want to check with your local cooperative extension for a list of approved pesticides and insecticides to keep the problem from getting out of hand.

Check Early and Often

The most important thing to remember when growing your beans is to keep a close eye on them in the spring. Turn over the leaves and check for eggs. As soon as you seem them, destroy them.

Mexican bean beetles left undetected can triple their population size in the time it takes for your beans to go from seedlings to mature bean producing plants.

What’s Bugging You?

What pest problems are you dealing with in your garden? Let me know in the comments.

4 Comments

N'Ckyola on June 18, 2018 at 3:29 pm

Thank you, thank you THANK YOU for this Audra! You know I hate bugs… Ick. I have since replanted & have planted some marigolds around the new crop. I plan to keep an eye on them everyday like you said, so here's hoping for more green bean harvest soon!
DivaGardener on June 18, 2018 at 5:45 pm

I'm glad that I could help, Nikki! I hate bugs, too! 🙂 Definitely check your new plants daily. You may still get some damage, but if you do frequent bean patrols, it should keep the damage to a minimum.
Monika Borua on August 14, 2018 at 7:02 am

Thanks for the tips for growing beans. We generally plant both bush and pole varieties. We use our fence for growing the pole variety.
https://www.roysfarm.com/growing-beans/
DivaGardener on August 14, 2018 at 9:56 am

Hi, Monika:
You are most welcome! Thank you for stopping by. I hope you'll visit again.

The Most Common Problem With Growing Beans and How To Treat It