is our second spring living in a rural area and in late October
we suffer a plague of what we believe to be grass grubs in their
flying stage. They are decimating the new foliage on stone fruit
trees, myrtles and some roses. We do not want to use insecticides
and have been using organic natural sprays, but this is becoming
expensive. Can you suggest a homemade remedy?
sounds like either the common grass grub beetle (also known as brown
beetle) or bronze beetle, or both. Bronze beetle is a native insect
which has happily moved from feeding on native plants to exotics
and horticultural crops. Both beetles can cause significant damage
to a wide range of trees and shrubs in spring, chewing leaf edges
as well as eating holes through leaves. They are difficult to control,
even with conventional pesticides, as by the time you realise you
have a problem it's usually too late - the damage is done and the
beetles have generally moved on. And if you do find them on plants
and try to spray, they usually just fly away. In some seasons damage
can be worse than in others.
If you want to attempt
some sort of control without using insecticides, I can only suggest
you try spraying susceptible plants with something like garlic or
perhaps chilli spray which may deter the beetles from feeding on
them. But you'd have to apply it in anticipation of the beetles
flying, which isn't easy to time right, as weather conditions have
a great influence. To make matters worse, the effectiveness of these
sprays is also greatly reduced by rain.
The larvae live in the
soil, so cultivating around susceptible plants in winter is said
to reduce bronze beetle numbers but, like grass grub beetles, they
can fly in from elsewhere. Perhaps other readers have advice they
could pass on.
Gardener, Issue 187, 2005, Page 33
Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.