Biological control of beetles: how to keep green beans naturally

Beans of all varieties are fairly easy to grow but, like all plants, they have their share of diseases and pests that can decimate a crop. A great marauder is the beetle, and let me say that these marauders come not only in one variety, but in many different types. How to keep beetles away from green beans and other legumes may not be the burning question of our time, but if you are a gardener who has put his heart and soul into the bean field, you want answers.

Help, there are beetles on my green bean plants!

First of all, don’t panic. You are not the first and you will not be the last to find beetles on your green bean plants. If you are trying to identify the beetle, you’d better find a way to control the beetle in your green beans.

• The Japanese beetle – A pest can be the Japanese beetle. These pests were inadvertently brought from Japan and spread rapidly throughout most of the eastern United States. They are easily identified by their metallic green abdomen and tanned wings. If you live in the western or southern part of the United States, the Japanese beetle has not established itself there, so it is likely that your beetle is of a different type.
• Mexican bean beetle – Another beetle infestation could be the Mexican bean beetle. Adults and larvae chew on the underside of leaves, young pods and stems, leaving a ghostly, jagged, leaf-like appearance. Adults are about ¼ cm long and look like large yellow ladybugs with 16 black dots on their backs. The larvae are 13 inches long with six spines arranged longitudinally along their orange to yellow backs.
• Cucumber beetle – The cucumber beetle could be another beetle parasite. They also look like ladybugs but are yellowish green with 12 black spots. You will find these beetles eating green bean leaves as well as sometimes melons, pumpkins, cucumbers, eggplants, peas and some vegetables, leaving a skeletonized version of the foliage.

All these beetles are also known to feast on the pods of growing beans, leaving unsightly holes in the fruit.

How to keep beetles away from green beans

When you first see the beetle’s opponents, your first instinct is to eradicate them immediately, but how do you control the beetle? Well, I know that some of you are thinking of «insecticide» and if it is true that this is the most direct way, it is too easy! Try to get your hands dirty first and use insecticide only as a last resort.

Biological control of beetles in its most basic form is hand-picking. This is the first line of defense if you are not disgusted and the numbers are not too discouraging. Try hand-picking early in the morning when the beetles are slow. Tear them off the plant and pour them into a bucket of soapy water. They can be so lethargic that when you try to pull them out, they fall off the plant onto the ground or onto their lower limbs. Try placing a light-colored material under the plant to detect abandonment and get rid of them more easily.

Another means of biological control of beetles can be the use of traps. They can be found in the local garden centre. None of these methods will completely control the population. You only have the adults. Biological tactics may be necessary to win the war.

For example, in the case of the Japanese beetle, the larvae begin to hatch in mid-summer. This is the best time to use your arsenal of biological controls to eradicate pests. Parasites, nematodes and fungi are some of the methods available to control the Japanese beetle. Give the beneficial insect-eating nematode a chance. You can also try Bacillus thuringiensis, an insect toxin that poisons the beetle’s stomach, or Bacillus papillae bacteria, which infects worms with the milky spore disease and seeps into the soil to prevent future generations.

Additional controls for biological beetles

Other options are the introduction of beneficial insects such as :

• Beetles
• Green lace
• Hacking error report

They are all predators of the egg and young larval stage of many beetles.

Also apply diatomaceous earth around the plants. Try a spot treatment with combinations of insecticidal soap and neem oil. Be sure to completely cover the upper and lower leaves. Treatments should be repeated every seven to ten days if additional beetles are found.

Consider planting early maturing bean varieties to control Mexican beetles, which are at their peak during the summer. Plant a zinnia or marigold trap away from the garden to attract beetles to a tastier meal. Also, insert garlic or chives between the beans. The strong smell often deters beetles. Keep the area around the bean plants free of debris and remove any damaged or diseased foliage.

Finally, try using paper cups to protect seedlings or add a thin mosquito net or row cover to crops, attached to the sides to prevent adult beetles from entering. Keep in mind that all of these biological control methods take longer than insecticide control and you may have to fight with several methods, but the results are infinitely more durable and healthier for you and the environment.