Tree Died. Planting in the Same Hole.

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. 

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.

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

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. 

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.

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.