What Is Eating the Leaves of My Basil Plants?

Everybody loves the fresh, peppery-sweet taste of basil (Ocimum basilicum), but so do backyard bugs. Most people enjoy tossing the green leaves into salads and pasta dishes or mixing them into pesto. But garden insects prefer it right off the plant, and they often get there before you do. To control garden basil-munchers, you have to give your basil the best care, identify the insects eating your herbs, and then tailor a response to the pest at issue. Here are some tips for nurturing your plants, plus a short-list of the critters that could be eating them.

Basil
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Keep basil's lush foliage from falling prey to pests.

Growing Healthy Basil

A vigorous, healthy basil plant resists pests better than a weak one. Taking great care of your basil is just a matter of giving it a proper location and adequate nurture. Basil needs a full-sun site and well-draining soil that is rich in organic matter. Don't squeeze basil between other plants. Give it ample elbow room to allow good air movement. For best growth, basil needs regular watering, but avoid overhead irrigation. Basil works well as a container plant, so you can grow it in any region.

Identifying Hungry Insects

When a garden pest is chowing down on your pretty basil leaves, it is most likely to be Japanese beetles, slugs, aphids or leafhoppers. Each one leaves "evidence" to help you identify the culprit. Once you figure out which one it is, you can take action to rid the plant of its insect pests. Start with natural remedies before moving to pesticides.

Dealing With Bigger Pests

Begin keeping an eye out for Japanese beetles in late spring or early summer. They are chunky, metallic green insects that devour basil from the top down. However, they won't touch the leaf veins. If you see lacy-looking basil foliage, you'll know who has come to dinner.

How to get rid of them? First try picking them off by hand. These beetles usually feed during the day, and they are very visible. Another option is to place a bowl of soapy water under the basil and shake the plant repeatedly until you dislodge the bugs. You'll also find special Japanese beetle traps in garden stores.

The other large pest that loves basil is the slug. You may not catch them chewing holes in the plant leaves, because they eat at night, usually when the weather is wet. But slugs don't pass without a trace; they leave slime trails wherever they go, including up a basil plant. You should suspect slugs if the holes appear in the lower leaves and stems rather than the upper sections.

Slugs, too, can be picked off by hand if you are willing to track them down after dark with a flashlight. If you are a bit too squeamish for hand-collecting slugs, set beer traps for them. Put out low bowls of beer under the plant, and check them first thing in the morning. Another option is to make a circle of diatomaceous earth around the basil plants. This product contains sharp grains that scratch slugs that cross it, leading to dehydration and death.

Ridding Basil of Smaller Insects

Not all bugs eating basil are large enough to spot and grab easily. For example, if your plant has aphids, you aren't likely to see them. Rather, you'll notice that your basil plant's tender leaves look deformed or are turning yellow. Aphids are very common garden pests that look like moving dots on the leaves. They only become worrisome when their populations soar. That's when you'll notice plant damage. This usually happens when ants get involved by "managing" the aphids to eat the sweet substance they excrete, called honeydew.

In the battle for the emerald leaves of your basil, dish-washing soap is a powerful weapon. Mix a few tablespoons of liquid dish-washing soap into a gallon of water. Spraying this on the basil leaves gets rid of aphids quickly. After a few minutes, rinse the soap (and dead aphids) from the plant. Alternatively, use insecticidal soap to do the deed. Another alternative is to bring ladybugs or other aphid-eating bugs into the garden.

If the pests eating your basil leaves are a species of leafhopper, you are also unlikely to see them. These bugs are less than 1/4 inch long, with neutral tan coloring. But you won't miss their impact. They dig channels into the basil leaves, and it is these that give them away. Deal with leafhoppers by spraying the plant with horticultural oil, neem, or insecticidal soap. As a last resort, use organic pesticides that contain rotenone or pyrethrum as a base.