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Tuesday, January 12, 2016

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.


  1. Do these eggs overwinter? If so, then I would assume dormant oil applied now would smother the eggs.

    Also, the white latex paint also might fill in gaps in the bark that would otherwise be a preferred egg laying area for the pest.

    1. Eggs are laid during the growing season for sure. Their time of flight is not known and it is possible it is variable since I have found larvae in the tree during the winter of different sizes but never as pupae. This makes me believe their emergence, flight and mating times might be variable through the growing season.

  2. How about Dormant Oil? Let year we had Davey Tree out here and they switched us to an annual application of DO on al our fruit trees to prevent borers. Do you have any experience with this? We didn't have any signs of the boaters last year, but like you said, the damage usually shows years after.
    I found some DO for sale in the nursery and applied it to our grapevines and it REALLY cut down on white flies last year (or maybe it was the humid spring, who knows!) It sure was nice not to battle those little demons all season!

    1. Dormant oil will not prevent borers. They are good for some other pests though including aphids, scale and spider mites. It is possible to prevent borers from entering the trees but it would require many many applications of conventional pesticides to the trunk and limbs and no one wants to get involved with that. It is believed that sun damage to the trunk and limbs attracts borers and their egg laying. For this reason preventing sun burn the trunk and limbs is a main focus on preventing borers. Using whitewash on the trunks and limbs is a common way to help prevent the cycle of sunburn and borer damage. You can buy the old fashioned whitewash made from lime or you can make some with a 50/50 dilution of white LATEX paint and water and applying to the trunk and upper surfaces of major limbs. When borers are present (you can see their jelly like oozing from limbs after a rain) then cut them out with a sharp sterile knife and let the tree heal.

  3. Growing your own fruit ranks pretty highly in the satisfaction stake. Planting a fruit tree is easy and the results rewarding. Their explanation