Eriophyid mites are insect relatives in the Eriophyidae family. The majority of species of mite in this family are undescribed and many have complex life cycles that are yet to be fully understood. Eriophyid mites are tiny, often "carrot-shaped", and can only be seen with magnification. They typically have only two pairs of legs. Many are associated with plant foliage and live on host plant leaves.
Some cause leaf bronzing or yellowing that is often referred to as "rust". Other species produce galls on the leaves, buds, or flowers of their host. They may be referred to as blistergalls, pouchgalls, bladdergalls, fingergalls, spindle galls, or felt-like patches often called "erinea" depending upon the species of mite involved and the shape of the gall that it induces production of on its host plant. Other species cause leaf-curling symptoms or witches'-brooming. Some eriophyid mites are involved in the transmission of certain plant viruses. (Keep in mind that not all galls are produced by eriophyid mites; certain species of aphids, adelgids, phylloxera, and psyllids also produce galls on their host plants.) Often the "damage" created by eriophyid mites is minorly aesthetic, and can be tolerated on the host plant. In some cases, depending upon the species of eriophyid mite involved, noticeable disfiguration of the tree or shrub parts affected occurs.
Knowledge of the identity of the tree or shrub species is the first step in narrowing down frequently encountered gall forming organisms, such as the eriophyid mites. Many species will be specific to a single or limited number of host plants. Often due to their tiny size, these insect relatives go unnoticed until galls or other symptoms become evident on the tree or shrub. Monitor for off-colored foliage or leaf, bud, or flower abnormalities. If gall-forming insects are not detected, observe the material with a 10-20X hand lens.
Prune out and destroy witches' brooms or heavily galled sections of host plants, where practical.
Depending upon the species of eriophyid mite involved, certain species of predaceous mites do attack these insect relatives. For example, predaceous mites in the family Phytoseiidae are reportedly common when privet rust mites (Aculus ligustri) are present (Johnson and Lyon, 1991). The natural enemies of eriophyid mites will be specific to the species of mite of concern.
Abamectin (NL)
Carbaryl (L)
Horticultural oil (L)
Pyrethrins (L)
Pyrethrin + piperonyl butoxide (L)
Spiromesifen (L)
Chemical management options for eriophyid mites are available, however we would like to stress here that this type of intervention is often unnecessary. The species of eriophyid mite involved, and whether or not the damage it causes to its host significantly impacts the overall health of the tree or shrub, should be considered on a case-by-case basis. Often, eriophyid mites cause little more than aesthetic interest and chemical management is not necessary. In some cases, eriophyid mites can create galls or witches' brooms that seriously disfigure plants. However, the ability to tolerate the presence of these insect relatives should be evaluated depending on the mite involved and site-specific observations.
The host plant and the type of damage caused depends upon the species of eriophyid mite involved. Many miticides are ineffective at managing eriophyid mites. Mites sheltered and protected by galls will not be effectively managed by contact pesticides.
Active ingredients that may be applied systemically include: abamectin (injection).
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
