Recently published studies have suggested that the grape erineum mite is a possible vector of grapevine pinot gris virus. The economic status of this pest would change considerably if further research verifies this to be true.
Adult erineum mites are only 0.2 mm long, and a dissecting microscope is required to observe them properly. Their creamy pale bodies are elongate with only two pairs of legs. Although erineum galls can be confused with certain fungal diseases or phylloxera leaf galls, their characteristic appearance is the best way to identify these pests.
The hemispherical concave galls, or erinea, formed on the undersides of leaves initially have a felty white appearance due to the presence of densely packed long leaf hairs. Opposite to these galls, bumps will be visible on the upper surfaces of leaves. These swellings are a reddish colour in spring and turn green as the leaves mature. Small numbers of mites feed on the dense hairs in each gall, which eventually turn brown.
Adult erineum mites overwinter under the scales of buds. In spring, mites move to developing shoots and create galls on young leaves around the fruiting zone. Several generations are produced each year, with new galls developing higher up the shoots. Beginning in late summer, adult mites move back to the buds for winter.
Leaves with erineum galls appear to function normally, and there is little or no economic damage to mature vines until almost all leaves are covered with galls. Even then, damage usually only occurs if vines are also suffering from other stresses. Establishment of newly planted vines can be delayed somewhat by erineum mite feeding that will reduce fruiting.
Two other forms of erineum mite, the leaf-curling strain and bud-inhibiting strain, have been reported recently from Washington state and are possible in B.C.
The former causes slight to severe downward curling of leaves in summer with stunting of shoots and increased growth of lateral shoots. Feeding of the bud-inhibiting strain on buds causes a range of abnormalities, including scarified shoots, short zigzagging internodes, dead terminal buds and malformed leaves.
Erineum galls are usually very apparent during routine vineyard operations. Grape varieties differ in susceptibility to this pest, and it is important to check individual blocks for the presence of mites.
In order to prevent premature loss of leaves, new vines should be inspected and treatments applied if large numbers of galls are found on most leaves during the spring or summer months.
For more information about chemical control, see the Pesticides page.
The western predatory mite (Galendromus occidentalis) is an important erineum mite predator. Predaceous thrips will feed on exposed mites, but their effectiveness is likely limited when mites are protected within the dense hairs of the galls.
New plants may become infested in the nursery. Ensure that material used to establish new vineyards is free of mites and other pests or diseases.
Removing galled leaves can control light infestations to some extent. Research conducted in the Okanagan Valley demonstrated that removal of infested leaves in May did not alter yields or fruit quality.
Removal of basal leaves in June for leafhopper control will remove a significant portion of the erinea galls.
