Garden Pest: Mexican Bean Beetle

mexican bean beetle
Adult Mexican Bean Beetle

The Lady Bug’s Ugly Distant Cousin Twice Removed

Like all things worth doing, gardening comes with ample opportunities to fail.  Not that it’s all bad, but realistically failure will happen on occasion, and the best thing we can do is learn from it.  It’s called growth.  Well, my most recent garden failure is related to a known pest called Mexican bean beetle.  This clever critter disguises itself as a ladybug (it actually is a ladybug species that happens to be a vegetarian), while laying eggs on my bush beans and slowly devouring the leaves thereof.  When the eggs hatch, the larvae have no mercy: chewing away leaf tissue and bean pods, leaving nothing but a ghost of a plant. For detailed biological information about Mexican bean beetle, check this out.

Why is this a failure?  Because I knew it could happen and could have done things a bit differently to prevent this catastrophe.

mexican bean beetle
Contender Green Beans leaves damaged by Bean Beetles.

This was my second crop of bush beans.  The first crop ran its course, bearing heavily through the first wave of production, resting a couple of weeks, then ramping up for a last hurrah harvest before playing out.  During that time frame (June through mid-July) I saw a few Mexican bean beetles and noticed the population slowly increasing, but I finished harvesting and removed  the first crop before there was any real damage.

My first mistake was that I had planted the second crop while the first one was still in place. This allowed the mobile adults to fly on over to the new planting at will, especially once the first crop was removed.  While the larvae were destroyed on the first crop, there were already eggs laid on the second crop before the first was even out of the ground.  A better course would have been to wait a few weeks after having removed the first crop before planting a second one.

mexican bean beetle
Fuzzy baby bean beetles feasting away on a green bean leaf.

My second mistake was that I planted the second crop too close to the first one.  My garden is laid out in a series of 4×12 foot “beds”, and while I am good about rotating crops according to a plan, that plan had these crops bordering each other.  A better situation would have been to have the two bean crop locations separated by at least one bed.

It is true that I could have picked up some bug killer and knocked out the little pests; but to me that’s kind of like kicking over the table when I lose a game of checkers.  I’ll survive without the extra beans.  The next game starts now, though.

mexican bean beetle
Bean Beetle eggs laying in wait.

To prevent decimation of next year’s crop there are a few things I will do.  First and foremost is  to clean up the mess. Mexican bean beetles hibernate in accumulated dry leaves, etc.  To get rid of them I’ll rake up the debris between crops and destroy it prior to replanting an unrelated crop on the same bed.  I’ll also do my best to attract a diversity of critters to the garden, as this tends to limit population explosions for individual species. That means inter-planting and under-planting wherever possible, and keeping cover crops on those beds not actively growing crops. We might able to sneak in one more green bean planting before it gets cold. But, lesson learned for next season.

Happy gardening!

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