Friday, September 10, 2010

Mexican Bean Beetles

Every year brings its own trials. This year, the Mexican bean beetles have been ferocious. At the Plant-a-Row-for-the-Hungry garden, we tried spraying with Neem, but that didn't seem to bother the beetles at all. At home, I've just been smashing them, one beetle (or larva) at a time, but the beetles are winning. This is what most of the leaves on my pole beans look like:



And this is the adult form of the critter that is turning the bean leaves into lace:



The adult beetle looks enough like a ladybug (it is even in the ladybug family!) that most people would think it's a good guy. They would be wrong.

When the beetles are mature, they lay eggs, clusters of yellow dots. At some point, these eggs will hatch.



When the eggs hatch, what comes out doesn't look at all like a beetle. It is a fuzzy yellow larva. The larval stage of this beetle is heck on the leaves of bean plants. When I was looking for larvae to photograph, I couldn't find any young ones. These (below) have gone, I think, into the pupa stage.



When the pupa completes its development, it breaks out of its husk (like cicadas do) in the more familiar beetle form. There is an empty husk on the upper leaf in the picture below.



The big question is what to do about all these beetles. I am thinking about pulling up all the pole bean plants, but I still have cowpeas growing in another part of the garden. I am concerned that, without the pole beans around, those cowpeas will look a lot more tasty; right now, the cowpeas are bean-beetle free.

I have read that adult beetles overwinter in leaf litter, so I am definitely going to be turning the garden's soil some this winter, to make sure that remaining adults are exposed to whatever cold we have this year--- but last year we had a very cold winter; I am not sure how so many beetles survived!

4 comments:

  1. This is my first year dealing with them. I just ripped out all the beans today and got as much of the leaf litter as I could, but I'm sure I'll be in for a battle next year. I did notice that they didn't bother my spring crop, so maybe I should grow all of them for freezing too in the spring next year?!

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  2. Ahwk! I had the same problem with Mexican Bean Beetles both last year and this year too! I sprayed with Neem also, but it had zero effect. I lost the battle of picking them off the plants...they just got ahead of me. Strangely enough, although my green beans were decimated and I got slmost no yield, my pinto beans came through fine. I let them dry on the vine and by the time that happened, all the leaves had been skeletonized...but I got a huge dried pinto bean harvest. Go figure..

    Re Erin's comment, I am going to do an early planting and see if that helps. And this year I'm going to start picking the bugs off early and check the plants every hour if I have to! There must be something besides just turning the soil that we can do to kill them! Perhaps putting black plastic over the garden and leaving it there will kill them?

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  3. Erin and Gardenlady,

    Around here, the Mexican bean beetles don't get really bad, even in their very most abundant years, until late June, so earlier bean plantings are usually more successful. It is just ironic that this is the year I had decided to plant pole beans, two different kinds, in hopes of an extended harvest!

    Most years, I just plant bush beans in May and then pull those up when they start to look bad. But some years, the Mexican bean beetles aren't a problem at all.

    Last year is a good example of that. It isn't, I suppose, a huge surprise that I decided to try for an extended harvest of beans in the year following a low pest year...The longer harvest looked so very possible!

    This year has just been spectacular, though, in terms of the bean beetle population. A couple of years ago, it was the cucumber pickle worms that were so very bad, and this year those were just at their usual level, so it is possible that next year's bean beetles won't be so abundant, no matter what we do.

    Someone at the Plant-a-Row-for-the-Hungry garden said that he sprayed his beans at home with Sevin, but I am not interested in doing that.

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