As the pest starts to suck the sap from the plant, galls form where it lives and breeds. Extreme infestations can cause premature leaf fall, bud damage and death of entire plants. If mites infest blackberries, the fruit remains red and does not mature.
Gall mite [Eriophyidae]
The seriousness of the infestation varies greatly from year to year. Thousands of gall mites can live on each leaf. They are often overlooked because of their small size. Their damage is therefore often attributed to spider mites.
Gall mites affect a wide range of host plants. They overwinter in buds and withered fruit. In spring, the mites attack the new growth.