robinia - 2
of the branches of my Robinia 'Frisia' are quite brittle
and there are holes riddled throughout the trunk, indicating borer.
The roots of the tree also seem a little unstable - I can lean against
the trunk and the whole tree moves slightly, roots and all. Is there
anything I can do to save the tree - any treatments available for
the borer? Also, is it possible the borer from outdoors will migrate
indoors into my furniture?
sounds as if your robinia has suffered severe borer damage. If enough
of the stems are damaged, roots will also die off, causing the movement
you describe. It's a native insect which can affect quite a wide
range of trees and shrubs, and while the adult only lives for two
months or so, the larva, which causes all the damage, can spend
almost two years boring tunnels causing major damage to otherwise
little you can do to control this type of borer unless you're lucky
enough to catch it before the larvae has tunnelled very far into
the stems. During summer, look out for signs of fresh borer activity
indicated by fresh droppings, which look like blobs of fine sawdust
exuding from holes in the stems.
You could then try pushing
a thin wire into the holes, which may pierce the larva, or injecting
kerosene into the holes, but neither method has a high likelihood
of success. You could prune out dead and dying branches and encourage
fresh growth by watering and feeding, but if the borer has invaded
the main trunk there's not a lot you can do. Some robinias survive
for years with quite major borer damage, but they're unlikely to
reach their full potential, so it might be best to remove the tree
and replace with something similar, like Gleditsia 'Sunburst',
which in my experience seems less susceptible to borer.
The one piece of good
news is that this particular borer only feeds on living trees and
shrubs and isn't interested in feeding on your furniture. The borer
that does affect house framing and furniture is the larvae of an
entirely different fly.
Gardener, Issue 163, 2005, Page 28
Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.