Plant galls

A gall is a distorted growth of plant tissue, comparable to a benign tumor. It develops when the plant responds to an outside organism (an insect, mite, fungus, or bacterium) that manipulates its growth hormones to create shelter and a food source. Although often harmless, large numbers of galls can weaken a plant by diverting nutrients and reducing photosynthesis, slowing growth.

Signs to check

• A solid swelling or growth that is part of the plant and does not come off when touched.
• Widely varying shapes: round, elongated, pointed, or hairy, ranging from a few millimeters (fractions of an inch) to several centimeters (an inch or more).
• Growths on any plant organ, most often leaves and stems, sometimes roots.
• Variable color (green, reddish, or brown), which may differ from the original tissue.

What you may see

• Witches' broom · A dense mass of small, disorganized stems and twigs grows from a single point on a larger branch.
• Swollen or knotted roots · Roots develop swellings, galls, or abnormal growths that disrupt their smooth, regular shape near the crown.
• Gall or swelling on a stem · An abnormal growth, varying in shape and size, develops directly on the surface of stems or branches.
• Leaf galls or growths · Growths or swellings of varying shapes and colors appear directly on the tissue of leaves, stems, or veins.

What to do now

Observe and manage galls

1. Inspect the whole plant carefully to assess the number of galls. One or two are not a problem.
2. Cut off the most affected leaves or sections of stem cleanly with disinfected pruning shears. This is the most effective method because it removes the organism before it reaches adulthood.
3. Discard the cut material immediately in the trash, rather than your compost, to prevent larvae from completing their life cycle and spreading.
4. Watch the plant closely for the next 2 to 3 weeks for new galls.
5. Avoid any chemical treatment. Insecticides are ineffective because the gall fully protects the pest inside.

Prevention

• Inspect every new plant carefully before bringing it into your home.
• Maintain good air circulation around your plants to discourage flying insects.
• Check the undersides of leaves and new growth regularly, as these are preferred egg-laying sites.
• Keep plants healthy with appropriate watering and light to make them more resistant to attack.