Stem miners are insects with limited references in grower or scientific reports on poinsettias. Recently, in a poinsettia research study, a few scattered plants were found to have mines on the stems due to stem miners.
During a poinsettia research study at North Carolina State University, unusual stem symptoms were observed on a few main axillary stems of Euphorbia pulcherrima. Affected stems displayed beige tissue with longitudinal dark lines. The situation was only noticed due to a stem becoming detached. Otherwise, the situation would most likely have gone unnoticed within the plant canopy.
These symptoms are reminiscent of the dark trails caused by leaf miners in vegetable and ornamental crops; however, mining within the stem is rarely reported. The affected shoots did not die, and because the symptoms are covered by the leaf canopy, the situation would go unnoticed.
Dr. Matthew Bertone of the NCSU Plant Disease and Insect Clinic was quick to point out that stem miners exist. There are limited published resources documenting stem miners in poinsettia stems. Charley Eiseman reports cases of stem miners (Marmara gulosa) seen in poinsettias in California in 2002, but information is limited (Eiseman, 2022).
There were three poinsettia cultivars in the greenhouse, and only one, with thicker stems, was affected. There are scattered reports of stem miners in various other floriculture crops as well as certain trees. Reports of stem miners (Marmara sp.) have been made on blue lobelia and menispermum in Iowa in 2017 and 2018 (van der Linden, 2017; van der Linden, 2018). Similar symptoms have been observed on willows, elms, and ash trees, although these are estimated to be bark miners (Marmara salictella) (Wilson, 2014; Feldman, 2017; Feldman, 2019).
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