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American senna · Senna hebecarpa

What are these bugs on my American senna?

It is less common for this plant to suffer from major pest infestations, as it is quite hardy. When bugs do appear, they are usually aphids or caterpillars attracted to the fresh growth. Check the undersides of the leaves first.

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pests on a plant
Photo: Jules Verne Times Two, CC BY-SA 4.0

Check these first

  1. Inspect the undersides of the leaves for tiny insects.
  2. Look for sticky residue or shiny patches on the foliage.
  3. Check for chewed leaf edges or holes.

Likely causes

  1. Aphids

    Most likely

    How to tell: You see clusters of tiny green or black insects on the new stems and undersides of leaves. They often leave behind a sticky residue called honeydew.

    What to do: Spray the plant with a strong stream of water to knock them off. If they persist, apply insecticidal soap once a week for 3 weeks.

  2. Caterpillars

    Possible

    How to tell: You notice irregular holes chewed into the leaves or entire leaf edges missing. You might see the caterpillars themselves resting on the stems.

    What to do: Pick them off by hand in the morning or evening. For larger infestations, use a spray containing Bacillus thuringiensis.

Pests on other plants

Find out what's wrong with your american senna

The list above covers the usual causes. Pocket Botanist looks at a photo of your actual plant and tells you the likely cause, how serious it is, and what to try first. Identification and a health check are free.

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When to worry

A few bugs are normal in an outdoor garden and rarely kill the plant. You should only worry if the plant is losing more than 20 percent of its foliage to damage.

Stopping it coming back

Keep the plant healthy with proper watering and encourage beneficial insects like ladybugs to visit your garden.

American senna: pests? Check yours with a photo

Every plant is a little different. Take a photo of your american senna and Pocket Botanist tells you which cause is most likely, how serious it is, and what to try first. A few checks a day are free. Save the plant and you get care reminders timed for it.

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Questions people ask

Are these bugs harmful to other plants?
Aphids can spread to nearby plants, so it is best to treat them quickly. Caterpillars are usually specific to the plant they are eating.
Should I use a systemic pesticide?
Avoid systemic pesticides, as they can harm the pollinators that visit your American senna flowers. Stick to gentle soaps or manual removal.

Guides to these causes

More problems with American senna

Back to the American senna guide

This article was generated with AI on from the plant’s care profile and is general information, not horticultural advice. Read about how we build these guides.