Organic Insecticide Control for Bean Leaf Beetles

Reader Contribution by Tonya Olson
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Photo by Tonya Olson

When I was a kid, I hated picking beans. It was hot, humid, and eventually, I was sunburned from picking them. The work was intense, because my sister and I put off picking them until the bounty was heavy and the heat was high. Learn from my mistake: Don’t wait to harvest.

Beans also will stop producing if you don’t pick them. After all the picking was done, I had to trim the ends off. I heard it once said that green beans were a country kid’s worst nightmare. I know it was mine! I had eaten canned beans for most of my short life, and I didn’t really see the point to growing them.

Since then, I have become an adult and can now say homegrown garden beans are much tastier. Bush and pole beans are a couple of my contributions to our MOTHER EARTH NEWS garden. The inspiration for the pole beans came from my friend Benedict Vanheems, and as friend and former Mother Earth Living Editor Hannah Kincaid once said, try something new! The pole beans are my something new. We have yet to plant them in a circle, but because our garden grows in Zone 6a, we may very well be A-OK to do just that.

Because I have a vested interest in these beans, when I saw a ton of holes in them, the momma bear in me came out! I snapped pictures and marched back into the Ogden Publications office to ask our Editorial Director, Hank Will, for his advice. With Hank’s insight, we discovered the issue to be bean leaf beetles munching away to their hearts’ delight.

Identify the Treacherous Bean Leaf Beetle

Bean leaf beetles are 1/4-inch long and display many colors. They have four black spots on their backs with a triangle behind their head and are hard to control without chemicals. They thrive in moist climates such as ours and emerge in mid- to late-spring. Adults usually feed from underneath the leaf, while larvae feed on the roots, nodules, and stem below the soil. Luckily the beetles have not done much damage below the surface. We continue to see new growth, but the same shotholes are appearing on those as well.

Photo by Tonya Olson

The bush beans are fairing much better than the pole beans, which may have to do with where they are planted. Our pole beans are planted inline along the outskirts of the garden so that they can climb something — still to be determined. Bean leaf beetles tend to hang on the outskirts of fields, so it’s good practice to keep the perimeter around the garden trimmed or perhaps plant beans towards the middle of the garden.

Photo by Ingrid Butler

Naturally Neem

As a Great Plains country kid, I was not raised in an organic environment (were you?). My first thought typically would be to sprinkle some insect bug killer on the beans, but this is blasphemy in the MOTHER EARTH NEWS garden. I knew that wasn’t going to fly. I want to learn organic agriculture principles so that I can do it and share it! We found that the University of Wisconsin-Madison page directs organic growers to use rotenone, pyrethrum, or neem. Hank pointed me towards neem, so neem it is!

Neem is natural toxin that causes insects to lose their appetite, stunting their growth. Farmers in India also have harnessed the medicinal properties of neem for years. Read more in How to Use Neem Oil to Prevent Garden Pests. For such a small bottle it packs a punch! Neem conjures familiar smells for me, perhaps because it’s derived from an evergreen tree.

Neem Oil Insecticide Spray

Ingredients:

  • 1-1/2 teaspoons pure organic neem oil concentrate
  • 1 teaspoon mild liquid soap (to emulsify the oil in a spray bottle)
  • 1 liter tepid water

Directions:

Shake to mix. Apply once per week in the early morning or late afternoon to reduce drying time and make the topical treatment more effective. Apply while the temperature is below 90 degrees Fahrenheit to prevent damage to the plant (a risk if it happens to be water stressed). Be sure to hit the bottom of the leaf, because bean leaf beetles like to feed from the bottom.

Photo by Ingrid Butler

I have a feeling we will be trying Benedict’s pole-bean trellis idea in the middle of the garden very soon. Wish us luck!

Want to grow a garden as lush as ours? Find our go-to products for garden maintenance, harvesting, and more at in the MOTHER EARTH NEWS Garden Shed. If you’d like to be a MOTHER EARTH NEWS Community Garden sponsor contact Brenda Escalante.

Thank you to our sponsors, Garden In Minutes, Neptune’s Harvest, Coast of Maine, Southern Exposure Seed Exchange, Meadow CreatureLehman’s, Mother Earth News Store, Happy Leaf LED, Berry Hill Irrigation.