Encountering eriophyid mites on coneflower and other ornamentals

What are eriophyid mites? Eriophyid mites (family Eriophyidae) affect a wide variety of plants and are known as gall, blister, bud, or rust mites based on the abnormalities they cause in their host plants. Galls are abnormal growths on a plant that are often caused by plant hormones responding to irritation of cells due to insect, mite, or nematode feeding - or infection from fungi or bacteria.

Eriophyid mites live exclusively on plants and often develop and
overwinter inside leaf and flower buds. These mites are known for causing a wide range of distortions such as flower and leaf galls as seen on coneflowers by the Coneflower Rosette Mite and maple bladder galls caused by the mite Vasates quadrupeds. While this damage is mainly aesthetic, other eriophyid mites cause economic damage when not controlled. The tomato russet mite (Aculops lycopersici) causes discoloration of leaves and fruit in greenhouse tomatoes. Phyllocoptes fructiphilius transmits the Rose rosette virus to healthy rose plants causing life-long infection of plants with Rose Rosette Disease(RRD).

Each mite is specific to its host plant. Eriophyid mites are anatomically different from other mite species typically encountered in ornamental production. Unlike two-spotted spider mites or broad mites, all life stages (larva, nymph, and adult) of these mites have only two pairs of legs instead of four. Their legs extend from the front of a soft, carrot-shaped body. They feed by piercing plant cells with a dagger-shaped mouthpart and removing the contents. Eriophyid mites are very tiny (<350 µm or less than half an mm) and difficult to see with the naked eye. A 40x hand lens or microscope is needed to see them.

Eriophyid mites are very tiny (<350 µm or less than half an mm) and difficult to see with the naked eye. A 40x hand lens or microscope is needed to see them. Therefore, recognizing the symptoms of infestation is key in first determining mite presence. Visually, these mites look like specks of pollen or dust on the plant surface, and high numbers of mites together form a powdery-like appearance. Eriophyid mites move about plants on their own. Yet, due to their small size and the production of tiny threads, they are easily and primarily transported and dispersed by wind and greenhouse fans. They can also be easily moved by people and animals, including other insects – as well as on tools, clothing, and infested plant material. Large mites can be found venturing to the tip of coneflowers on windy days.

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