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The Greener View: Systemic Insecticides on Herbs

Jeff Rugg on

Q: In a recent article, you mentioned using systemic insecticides for aphids and other small insects. I have them on herbs, vegetables and some flowers in the garden. What kind of systemic insecticide would you recommend?

A: Systemic insecticides work by soaking into the plant. They can be dry granules spread on the soil or a liquid that is poured over the roots. Some systemics can be sprayed directly on the trunk or leaves. The insecticide moves inside the plant so that sucking insects like aphids or chewing insects like caterpillars can take in the insecticide. Systemic insecticides are less harmful to other insects that are not harming the plant.

Some systemic insecticides may move into flowers or the fruit of the plant. If it is in the flower, it may harm pollinating insects. If it is in the fruit, it may harm animals that eat the fruit. Insecticides don't last forever in the plant. If they did, we could treat the plant once and protect it forever. Because they break down, there is a time after the treatment that has been determined that the fruit is safe to eat.

Insecticides of all kinds that have food crops listed on the label will state the length of time that you are required to wait between application of the insecticide and the time of harvest. Since you are going to eat the herb leaves, there may be a long time to wait.

Read the label to determine if the herbs or crop you want to treat and the insects you want to treat are listed for that insecticide. Then look to see what the harvest interval is. If the herbs are not on the label, then you shouldn't use the insecticide. It may be that the insecticide was never tested to see if it would work on that crop. It could be that the insecticide damages the crop more than the insects. It could be that the insecticide breaks down so slowly in that crop that you can't harvest it safely.

Read insecticide labels at the store before you buy them. It may be that the flowers can be treated, but not the veggies. Insecticide labels are valuable tools for learning about product safety, directions for use, protections for the environment, safe storage, proper disposal of the container and many other things. It is wise to reread the label before each use.


As for treating your herbs for aphids, there are several things you can do. First, a simple blast of water from the hose may dislodge most of them. Repeated water sprays can keep them under control. Insecticidal soap and neem oil insecticides designed for crops can be used but remember that they are still insecticides. You need to read the label to fully understand if they can be used on your crops. Insecticidal soap can damage crops or be ineffective if the directions are not followed properly.

I do not recommend home remedies, including making your own insecticidal soap. Your dish soap is designed to wash oils off of dishes. Plants use oils to protect themselves. Washing plants with dish soap can harm the plants. The dish soap may also have fragrances, hand softeners and other ingredients not designed for use in the garden.


Email questions to Jeff Rugg at To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at




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