Q. The allium in my Connecticut garden have an odd, worm-like growth on some leaves.
Can you tell me what it is and if I need to be concerned?
There is a pest called allium leaf miner (Phytomyza gymnostoma) that you may be seeing. It has only been detected in Connecticut since January 2020, though it has been present in the Northeast since 2015. The adults make repeated punctures in an allium leaf in the spring that result in a string of spots or "bubbles" that resemble a worm or caterpillar.
I am sending you a link to the University of Connecticut Plant Diagnostic Lab's bulletin on this insect so that you can compare the image to what you are observing. This pest has led to failure of full leek and onion crops in nearby states and its range in Europe. It is certainly not a happy event to have it arrive in our area.
If you would like to send a plant sample to the Lab's diagnostic center for confirmation, the bulletin explains how to do that. If the problem on your leaves is not similar to what you see in the bulletin, please let us know and send along a photo to Plantinfo@NYBG.org. We would be happy to take a look.
Courtesy of NYBG's Plant Information Service
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