Aren’t those some of the ugliest beans you ever did see? Who’s going to want to eat those? It’s a nightmare to snap around the scabs and get a pretty plate of veggies. It’s not that there’s anything wrong with them per se or that you can’t eat them, it’s just that who wants to lift a forkful of food to their mouth with blatant evidence that someone else dined on your dinner first?
(Certainly, not my kids!)
And if they’re going to whine about scabby beans, that means that I’ve wasted a whole lot of time and energy growing and cooking beans for the last 3-4 months + 10 minutes.
So who’s been eating our dinner? That’s the question. And it doesn’t take much detective work to discover the answer.
The pest in this case, doesn’t cover his tracks well… or at all, so identification is a breeze. What we have here is the handiwork of a Mexican Bean Beetle.
The adult phase looks very much like a copper-colored lady bug, but please refrain from feeling excited that you have welcomed that most beneficial, red-cloaked beauty into your garden. This chap is an imposter.
Besides scabby, pock-marked beans, Mexican Bean Beetles will also rapidly defoliate your bean plant’s leaves. They start young and devour the leaf even as larvae.
Mexican Bean Beetle Eggs (Not to be confused with ladybug eggs which are shaped similar and stick up off the leaf on which they were laid.)
Newly hatched Mexican Bean Beetle Larvae (Notice the tiny yellow larvae and the white egg casings they are leaving behind.)
Mexican Bean Beetle Larvae. Eating their way away from their egg shells… notice the translucent leaf skeleton.
Large Mexican Bean Beetle Larvae. Their exoskeleton is actually clear. Squish them and you’ll notice that it’s their guts that are yellow.
So now that we have successfully identified our pest in the bean patch, what’s a “Beyond-Organic” gardener to do? Since we know that even organic pesticides kill life indiscriminately, we want to try to use methods of pest control that will not destroy either our pollinators or our biggest ally in the war against the bad bugs, beneficial insects. Here are some various strategies that you can try.
8 Ways to Organically Control Mexican Bean Beetles
Crop Rotation
Before you even have a problem in your garden, it’s very wise to practice crop rotation. It’s like tricking the bugs before they have a chance to outnumber you. Since many insects, including Mexican Bean Beetles overwinter in the ground near where they last had a sure food source, moving their favorite treats to another location next year will help to prevent another infestation.
We have gardened here 3 years and the 2nd year brought with it Mexican Bean Beetles, but because I rotated my crops, amended my soil, and didn’t space intensively last year, I was able to avoid having ANY Mexican Bean Beetles in my garden last year!
Row Cover
If you had a known problem with Mexican Bean Beetles last year, and have rotated your crop, you can try using insect netting (stuff like this) to keep them off your beans. When they come out of the ground and go looking for something to eat, they’ll pass right on by because they won’t be able to access your beans.
Trap Crop
Trap crops are a great way to trick pests into finding somewhere else to cause their destruction. Mexican Bean Beetles will be attracted to soybeans (Find non-GMO soybeans here). Once you find that they have infested the soybean crop, pull it, sack it in trash bags for a week or so, and then burn the crop to kill all the bugs and their eggs. Just make sure you don’t wait until they are into a second generation. It’s best to do this when you first find the bright yellow larvae so that they don’t get a chance to reproduce a 2nd or 3rd time first.
Choose a Different Variety
One similar method of control would be to grow a different bean variety, one that has a high initial yield, such as Provider. Harvest that crop, which will be around the same time you’ll start noticing a few bean beetles here and there, and then treat them the same way you would a soybean trap crop. If you didn’t get enough beans to meet your needs, try growing a second succession if you’ll have enough time before your first frost.
Predatory Insects
One of the most wonderful sights to see as you fight this battle is to discover you have an ally that was fighting while you were away. Thankfully, the Mexican Bean Beetle has a couple of predatory insects that will attack it. This summer I discovered what looked very much like my most despised enemy, the squash bug on my green beans. I was surprised to find it there, which was enough to cause my natural instinct to pause for a moment before squishing it. I’m glad I didn’t, because though it looked very much like a squash bug, it was actually a Spined Soldier Bug. (Aptly named, isn’t he?) Later, I spotted one with one of those golden larvae speared on the end of a Spined Soldier Bug’s mouth(?)!
Another predator of Mexican Bean Beetles is the Pediobsus foveolatus parasitic wasp, which you can buy mummies of online. They will parasitize the larvae and stop further generations from breeding and eating.
Hand Picking
This one is kind of a no-brainer, but Mexican Bean Beetles and their larvae are super easy to squish. Not stinky, and not explosively gooey. They are easy even if you’re the squeamish type (raises hand). I wrap the leave they’re eating on around them and pop their guts out. Try it. It’s victoriously therapeutic.
Milky Spore
Spray the larvae with Milky Spore which are beneficial bacteria that will kill them. Milky Spore will also attack the Japanese Beetle grubs, the adults of which are also are fond of attacking beans. Two for one deal!
Neem Oil
Unlike pesticides (organic or conventional), neem oil is a spray that you can use on your infested plants that will not kill all insects, including the beneficial ones (if you do it right). Neem oil will only affect the insects that are eating the leaves you spray it on. Just make sure you only spray during the early morning or late at night when the pollinators are through working. Spraying them directly with neem will kill them. Making sure that neem oil has time to dry first ensures that only the larvae on your beans will be affected when they eat the leaves. You can buy cold-pressed neem oil HERE.
Thankfully, there is hope when you find Mexican Bean Beetles in your garden! It might be too late for this gardening season, but it’s a comfort knowing that you have the knowledge and resources to beat the enemy next year and bring in a good crop of organic beans to feed your family!
What methods of controlling Mexican Bean Beetles have worked best in your garden?
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