Poplar bud gall mite

Distribution

Prairie Provinces, Western Canada

Western Canada The Prairie Provinces

Damage, symptoms and biology

Damage is usually confined to the lower branches of the tree's crown. Adult mites attack buds and unfolding leaf clusters in the spring; mites sucking the sap from the tissue cause further twig growth to stop and cauliflower-like swellings (galls) to form. The mites live in these new galls, which are dark green, succulent, and covered with minute hairs. By late summer the galls have become hard and dry, and brick red in colour. Galls remain active (i.e., inhabited by mites) for 1–4 years and may grow to 4 cm in diameter. Old or abandoned galls are grayish and hard, with a characteristic ridged and furrowed surface.

Trees affected with poplar bud gall mite lose their aesthetic value quickly because new galls are formed every year and old ones sometimes last on the tree for 5 or more years. A persistent infestation also causes the lower branches to become stunted and crooked, often resulting in branch death. The tree is seldom killed, but continued heavy attack may increase its susceptibility to other pests and to such adverse environmental conditions as frost or drought.

The adult poplar bud gall mite is a wormlike organism so tiny (0.2 mm in length) that it is invisible to the naked eye. A cluster of adult mites, feeding on new poplar buds or unfolding leaves, inject into the tree a substance that stimulates the formation of a gall around them. The mites that live inside this gall feed on the sap in the gall and produce a new generation every 2–3 weeks until October—eight or more generations each year.`

As the population increases, the gall grows in size, and an active gall may contain more than 3000 mites. All life stages spend the winter in the gall; in the spring, they either feed in the old gall or migrate along the branches to new buds, in which they initiate new galls. Galls are inhabited for up to 4 years and then abandoned. Mites are tiny and are easily dispersed by the wind to new localities where they initiate new infestations.

Other information

In areas where there is a high risk of poplar bud gall mite infestation, consideration should be given to the planting of more resistant hybrids, such as Walker and Griffin. An infested tree that is provided with adequate moisture, weed control, and fertilization can tolerate infestations of mites and gall development without major effects.

Control is difficult because mites spend most of their time inside the protective galls and reproduce rapidly.