Knopper Galls form as swollen, ridged outgrowths on acorns in late summer, and are caused by the tiny gall wasp Andricus quercuscalicis, which only arrived in Britain in the 1950s and has been spreading ever since. The galls are notably sticky and red, later becoming woody and brown. Interestingly, the spring generation of this tiny insect only develops in the catkins of Turkey Oak Quercus cerris – so for the insect to be present both native and turkey oaks need to be available to it.
In any given year 35-65% of the acorn crop can be affected. However there is a large and so far unexplained variation from tree to tree, with some trees showing very high galls levels while neighbouring trees are relatively unaffected.
JW
In any given year 35-65% of the acorn crop can be affected. However there is a large and so far unexplained variation from tree to tree, with some trees showing very high galls levels while neighbouring trees are relatively unaffected.
JW