Q. I have a major borer
problem with my nectarine tree. I will be removing it and replanting. Do I need
to treat the soil before I plant another tree?
A. No. The borers that are
problems in our climate (Pacific flatheaded borer or Flatheaded apple tree
borer) do not enter the soil during any part of their life cycle. The borer you
may be thinking of is the peach tree borer which we do not have in Southern
Nevada but is common in more northern climates.
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| Adult Pacific flat headed borer picture from Oregon State University |
The peach tree borer does not
actually enter the ground either but can be found low on the trunk near the
soil level which makes you think it does. Both of these borers spend their
entire life cycle either in the air as a beetle (our borers) or a moth (peach tree
borer) in flight seeking a mate and looking for food to sustain itself until it
can reproduce. The rest of the time is either as an egg laid on limbs or the
trunk or larva tunneling and eating in sapwood where it can find carbohydrates
for nourishment and growth. The final stage is pupal, also inside the tree,
where it transforms from larva to adult beetle or moth.
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| One of the flat headed borers in a damaged branch of peach |
Control by chemicals is
not very effective for our borer since we don’t know when it flies or where it
lands until we see damage. Having said that, there is one chemical that is very effective for controlling borers that are inside the tree and it is labeled for fruit trees. The chemical name is
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| One of the products recommended for borer control containing imidacloprid |
imidacloprid. It comes as several different trade or label names. One of the common names for homeowners is a Bayer product found in many local stores and nurseries. It is a systemic insecticide that moves up inside the tree killing insects that are feeding on the interior. The claim is for 12 month protection using this product. Personally, I have a problem applying systemic insecticides that last 12 months on plants which produce fruit that I'm going to eat in less than 12 months. But it is labeled to do this.
Instead I recommend that we focus on prevention by protecting trees
like peach and nectarine from sun damage to the limbs, We do this by keeping the canopy
full enough to shade these limbs or painting limbs with whitewash to reduce sun
damage by intense sunlight. Sun damage seems to attract the adults and their
egg-laying.
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| Midsummer die back of peach limbs due to progressive borer damage. |
On older trees, damage from these insects might be over several
years before visual signs of damage appear. At advanced stages of attack over
several years, we see limbs dying in midsummer. Early signs of damage can be
seen the day after a good rainfall when brown colored sap oozes from damaged
areas.
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| Sap coming from peach limb due to borer activity |
During early stages of
damage we can remove the outer bark of damaged areas with a sharp knife
exposing where they are living and feeding and revealing them to potential
predators and exposing them to the elements. When this kind of practice is done
on a regular basis we might see about 80% of the damaged trees recover until
the next onslaught. Borers in peaches and nectarines are the usual reason these
trees seldom survive past 20 years of age.
