Monday, June 3, 2013

Advance Phenology: Bean Beetles

(This one was written last summer. I'm posting it now in time for it to be useful to gardeners.)

Wet as the summer of 2012 was, Grandma Bonnie Peters found one organic farmer in Tennessee who managed to raise a few marketable vegetables. Like most local gardeners she had her best yields in beans...almost a third of what could normally be expected. This was, however, enough beans that bean pickers were invited to camp in the barn. And I wondered how it was possible for so many competent bean pickers to have harvested so few beans.

What I remember about picking beans as a child was that you use the skills you build by “Finding the Hidden Pictures” in cartoons in winter. There are beans back behind the leaves, but beans, leaves, and stalks are all the same shade of green. You have to focus on the shapes to see which of the green things before you are beans. The number of beans on a bush—these were bush beans, like the ones we used to plant—is approximately one or two handfuls.

This was a different experience. Most of the bean leaves were a dull sepia-brown lace, skeletonized by bean beetles. When I did see a bean leaf I’d turn it over and find six or eight bean beetle larvae busily reducing it to a lacy leaf-skeleton.

Bean beetles have spotted wing cases, similar to ladybird beetles, but bean beetles’ wing cases are bigger, flatter, and softer. Bean beetle larvae are bright yellow, with soft but bristly hair that forms a ridge down their backs. Having no noticeable brains, they will cling so greedily to a leaf, if they are getting any nourishment out of it, that the whole body can be crushed before the jaws let go. The hair is usually bright crayon-yellow like the body, but in a large and diverse population like the one we saw, individuals with white or black tufts can be observed. At no stage of a bean beetle’s life would most humans find it very attractive, but the adult beetles are less repulsive than the larvae. (Clear pictures, if not of the most typical individuals, here: http://entnemdept.ufl.edu/creatures/veg/bean/mexican_bean_beetle.htm)

The bean harvest would have been much faster and more profitable if the bean beetles had been systematically hunted down before they became so overpopulated. Bean plants with their leaves gnawn down to skeletons produce small, empty, spongy, leathery beans. If they had produced full-sized beans before being skeletonized, these beans weight down the dying plants, sag onto the ground, and are nibbled by insects. Bean beetles will not eat a bean pod if they can get a bean leaf, but enough hungry larvae had taken hopeful nibbles out of enough beans to reduce their market appeal.

“We should have just used Sevin Dust,” one of the farmers said despondently.

We never had to use Sevin Dust. Here are Seven Green Ways to control bean beetle populations:

1. Resist the urge to start a Vicious Poison Cycle. Bean beetles don’t have nearly enough natural predators. You do not want to risk killing any creature that will eat a bean beetle.

2. Don’t plant whole fields of just beans and more beans. Tradition says that corn, beans, and squash are “sisters” that grow best when planted together. Teaming corn and beans works more for the benefit of the corn (beans help to replenish some of the nutrients corn vacuums out of the soil) and for pole beans, which like to form vines and cling to something vertical, like a cornstalk. Tomatoes come from further south and can only be counted as cousins to the “sisters,” but they fit well into the family. Bean beetles are among the many creatures that don’t like the smell of tomato plants. Although, in these badly infested fields, even the rows of beans planted next to rows of tomatoes harrbored some beetles, they were clearly the beetles’ last choice; the plants had lasted longer and produced more typical amounts of beans per stalk. Basil, oregano, parsley, and sage are other congenial companions that exude odors humans like and most insects hate.

3. While bean plants are growing, inspect them every day or two. Pull up weeds while they’re small enough to pull up easily by hand, and at the same time, carry a pocket-sized container with a tight lid, such as a pill bottle or jelly jar. When you see a bean beetle, trap it in the container. If you see a larva, trap it too. When you’ve visited all your beans, or the container is full, whichever comes first, fill the container with baby oil or rubbing alcohol. Give the beetles a half hour or so to soak, then burn the dead bodies. This is not the warmest and fuzziest gardening chore, but think of it this way: poisons cause the beetles to suffer longer and also cause other animals to suffer, whereas drowning is a quick clean death and only the beeetles will die.

4. You can also discourage bean beetles by mixing dishwashing liquid soap with water in a spray bottle and spraying it on the leaves. Repeat after rain rinses off the soap residues.

5. Inevitably a few bean beetles will manage to produce larvae, and since these sluglike little animals are more aware of appetite than of anything else, you will see a few bitten beans. Technically these beans aren’t kosher-pareve, but non-Jewish people just cut off the bitten section and do not see or taste any difference in the clean-looking part of the bean.

6. If they’re not nibbled away by bean beetles or killed by root rot, bean plants will continue to produce beans for weeks. Eventually, however, the plants will still dry up, turn yellow, and stop bearing. The roots and spent stalks are still very attractive to bean beetles. Burn them. (It’s prudent to burn anything that shows damage by root rot  or fire blight.)

7. If at all possible, try to rotate your crops next year. Don’t plant any annual crop where you planted the same thing last year. Repeatedly planting the same thing in the same place is known as monocropping. Monocropping causes pest populations to explode.