The majestic Garry oak is under threat from urban development and encroaching trees, shrubs and the climbing vines of English Ivy. You can help reverse its decline while adding beauty to your property. The trees can live for hundreds of years. Growing and caring for a Garry oak tree is a project that you can do with your children to create a lasting legacy for your family. Plant acorns or seedlings and watch them grow.
One method of transplanting Garry oaks is to use the ‘sand and snorkel’ technique.
An acorn is the fruit of an oak tree. There is a nut containing a single embryo protected by a tough shell that hangs from a branch by a “cupule” or stemmed cap.
Garry oak trees have evolved with hundreds of different insect species, as well as a number of micro-organisms, and it’s perfectly natural to see nibbled oak leaves or leaves with small holes in them. Large spherical galls (1–2 cm, ½–1" “speckled oak leaf galls”) are caused by native gall wasps whose populations are kept in check by native parasitoids and do not pose a serious threat to Garry oak trees.
Introduced insect pests such as jumping gall wasps, oak leaf phylloxeran, winter moths and gypsy moths, along with the fungus-like organism that causes sudden oak death can be more problematic than native insects:
Jumping gall wasp: The jumping gall wasp lays its eggs on several ornamental oak species in British Columbia, but the Garry oak is the only tree species on which it can complete its life cycle and where it does the most damage. Tiny (1.5 mm, 1/16") yellow galls that look like mustard seeds on the undersides of the leaves house the wasp larvae. When the larva matures, the gall falls to the ground, and as the wasp moves around inside, the gall visibly and audibly “jumps”. Yellow-brown spots are left where the galls were attached to the leaves.
Symptoms appear in mid-June and include anything from simple spotting of leaves on lightly infested trees to complete scorching and premature defoliation on the most severely infested trees. Fortunately, there are some parasitoids that feed on and kill the gall wasp larva, and earwigs and some ground beetles eat galls. Although there are commercially-available insecticides, these are not recommended. For more information and photos see this Canadian Forest Service Leaflet (PDF).
Oak leaf phylloxeran: The damage from oak leaf phylloxera is first visible as yellow spots on the leaves in May and June. This gradually progresses to complete browning and defoliation of some trees by late July. By late July or early August, heavily affected trees lose their leaves, although the trees often produce a second flush of leaves in August.
Most trees with phylloxera seem to have light infestations without damage, while a few trees are heavily attacked year after year, becoming severely weakened and eventually dying. At least 10 species of predators have been recorded feeding on the phylloxeran, but they do not appear to control it.
Many Garry oaks recover from moderate infestations without treatment. However, if you are concerned that your trees are unhealthy, have an arborist with Garry oak expertise check them, as weakened trees may eventually succumb to multiple or repeat infestations.