June 2012

 

In Western Colorado as with many other areas that produce stone fruits, our orchards are subject to damage by the peachtree borer, Synanthedon exitiosa, AKA Crown Borer (CB). 

Although primarily a pest of peaches, this insect will also attack nectarine, plum, prune, cherry, apricot, and almond. The original host plants of this native insect are thought to have been wild plums and cherries.

 

The adult borers are striking clear-winged moths with yellow and steel-blue body markings. The adults of these insects have from one to four yellow-orange stripes across the abdomen, depending upon species and sex. CB enters the tree near soil level and does not require the presence of wounds or breaks in the bark for entry.

 

 

The peachtree borer overwinters as a partly grown larva in its burrow beneath the bark of the tree. In the spring, feeding is resumed and the larval period is completed. When mature, the larva constructs a cocoon under the bark at or near soil level and pupates.  Adults emerge June to September, depending on the maturity of the larva when it overwintered. Since everything else is running historically early this season, I would expect CB to follow the trend. It’s not unusual to have continued trap catch through late September into early October.   Mating can occur the day of emergence with the start of egg laying immediately after.  Adult females can stay active laying eggs into late summer, early fall. A fact that I believe is key to some of our infestation problems (more on that in a moment).   Most eggs are laid on the lower 6 inches of the trunk.  There is one generation per year.

 

When the eggs hatch, the CB larvae tends to crawl down the tree to soil level and burrow in at the root crown (hence the name).  Injury is caused by larval feeding on the cam­bium and inner bark of the trunk close to the soil level. Larger roots can also fall victim.   Basically the sap flowing from the root is cut off at the soil line strangling the upper portion of the tree. 

 

Trees that are attacked will have masses of gum, mixed with frass, exud­ing from the bark at the soil line. All ages of trees can fall victim. Young trees are at times completely girdled and subsequently die. Older trees are often so severely injured that their ability to produce is reduced and they are rendered especially susceptible to attack by other insects or by diseases.

 

CB larvae can take up to two years to develop (while they feed inside your tree), so any control measure a grower would elect will require repeating for at least 2–3 years if a population has established a foothold.  Once inside the tree, CB larvae are pretty much immune to control measures.

 

Traditionally control for CB has been to apply a trunk drench in early July with a material such as Asana.  This application is aimed at newly hatching larvae.  While this program can be very effective, it has a couple of problems.  It is a very labor intensive program that takes large volumes of water to obtain complete coverage of the tree trunk.  Using the lower nozzles on your orchard airblast will not get the job done!  This is a handgun job.  The second issue is the length of control needed.  Remember my earlier comment on the period of egg laying?

 

Understandably most growers apply the early July spray, then it’s “all hands on deck” for harvest.   The problem arises from the fact that a single application of insecticide will not protect you for the three plus months of egg laying that occurs.  At a minimum this should be a two spray program.

 

However, there is a good alternative in the form of pheremone mating disruption (MD) for the control of this perennial pest.  Isomate-P twist-tie pheromone dispensers are la­beled for use against this species. They are placed in the trees at a rate of 100–200 ties/Ac at or before the first flight, with the higher rate  recommended when pest pressure is high.   An application of this pheromone just prior to emergence will provide season long control of CB.  If you have an established population in a block, the combination of pheromones and trunk sprays will provide the strongest control.  

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