CO-Horts

CO-Horts

Tuesday, February 12, 2013

Piñon pines under attack in SE Colorado

Posted by:  Linda McMulkin, CSU Extension-Pueblo County

In southeastern Colorado, Pinus edulis (Piñon) and Juniperus monosperma (One-seed juniper) are part of the native landscape and we often look at them as indestructible.  Unfortunately, our piñon are under attack by an insect that most of us didn’t know much about until two years ago.  The damage caused by piñon pitch mass borer in natural areas and local landscapes has been devastating.        
I’ve personally visited more than 30 sites in various parts of Pueblo County where one or more piñon showed symptoms of piñon pitch mass borer (Dioryctria ponderosae).  The Colorado State Forest Service office in Cañon City reported that they have seen infested pines in Fremont County and a local rancher says he has found evidence of infested piñon in northern Huerfano County.  While the problem is primarily on piñon, I’ve found evidence of the insect on Ponderosa (Pinus ponderosa) in landscapes in Pueblo West.  In the Midwest, the European native Scots (Pinus sylvestris) and Austrian (Pinus nigra) pines have also been attacked, but we haven’t seen piñon pitch mass borer on those species in Pueblo as of early 2013. 
Many pines are overwatered in urban landscapes, making them more susceptible to pitch mass borer due to excessive succulent growth or bark cracks.  And while many of the plants I’ve examined are in landscapes, others are in unirrigated natural areas.  Those trees are likely weakened due to the continued drought in our area.  
Fresh and dried pitch on Pinus edulis
Photo by CMG Sylvia Sanchez.

Infested trees look stressed, with thinning or browning needles.  The most noticeable sign of infestation is pinkish pitch on the trunk or larger branches, often near the branch crotch.  The pitch is spongy and sticky, about the texture of chewing gum on a warm day.  Pitch will drop onto lower branches and dries to a cream color. 
The insect, a small moth whose larval form is a wood borer, is responsible for reduced vigor and tree death.  The adult insect is small and may be unnoticed in most landscapes.  It is a moth, about one-half to three-quarter inch long, grey- brown in color with white markings.  The adult emerges from the infested tree June to August, leaving a small hole in the bark.  Eggs are laid on the bark, often near wounds, pruning cuts, or the crotch of the larger branches.  The larvae, a tan worm with a brown head, tunnel under the bark and feed on the vascular tissue of the tree.  
Pitch mass borer larvae and fresh pitch.  Photo by: 
Dr. Whitney Cranshaw,  Colorado State University, Bugwood.org


            An interesting characteristic of this insect is that the larval stage can last for one or up to two years, depending on weather conditions.  Eggs are laid from late June to August and hatch from one to four weeks later.  The larvae go through four molts and then pupate in a pitch and silk-lined chamber in their tunnel.  In Nebraska, the life cycle can take 14 to 24 months.  Dr. Whitney Cranshaw, CSU Entomologist, reports that the life cycle of Dioryctria ponderosae in Colorado is at least 2 years. 
             Officially, once the larvae are under the bark, chemical controls are ineffective, but you can try to stab the larvae inside the tunnels with a flexible wire.   Unofficially, local nurserymen and gardeners report that soil drench products containing Imidacloprid, labeled for some types of deciduous trees borers, has been effective on pines.  No research on the effectiveness of this chemical on pitch mass borer has been published and the insect is not listed on product labels, so there is no guarantee that it will be effective.  But I stopped by to check a couple of tress that I know were treated with Imidacloprid last summer and they show no additional signs of damage.  Actually, they look great, which I didn't expect after what I saw last spring.

1 comment:

  1. Linda, I have seen this here periodically - last year outside of Cedaredge in Delta County - but only in landscape trees. It's scary to think about it spreading in the PJ! I have been concerned, with this drought situation, that we would see another flare-up of pinyon ips, which wiped out so many following the 2002 drought, and now something more to be on the lookout for!

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