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Insect and Disease Associates of the
Pifton-Juniper Woodlands
Terrence J. Rogers 1
Abstract.-In order to successfully manage pinon-juniper ecosystems for
sustainability and social needs we must also look at and understand the
role of insects and diseases associated with this ecosystem. At the present
time, however, little is known about the role of insects and diseases in the
pinon-juniper ecosystem. This is not really surprising since' until just
recently, last ten years or so, the pinon-juniper type was managed primarily
for forage production with some considerations also being made for
fuelwood and pinon nut production. With the advent of the Forest Health
Initiative and the Pinon-Juniper Initiative, however, a more in-depth
understanding of the role insects and diseases play in the pinon-juniper
woodlands and their potential impacts on management objectives is
necessary if we are to manage this system for sustainability and desired
social needs.
INTRODUCTION
Twig beetles, Pityophthorus spp. and Pityogenes spp.,
are frequent pests of pmon pines. Normally they
attack shaded-out and storm-damages twigs and
branches.
Occasionally, however, twig beetle
populations locally build-up in drought-stressed
injured trees. When at out break levels, entire
viewsheds and landscapes can be affected.
Outbreaks of the pmon needle miner,
Coleotechnites edulicola, and the pmon pine needle
scale, Matsucoccus acalyptus, also occur during
periods of below average precipitation levels and
can cause widespread defoliation damages to
viewsheds and landscapes. Several years of heavy
defoliation damages can predispose infested trees
to Ips bark beetle attack and subsequent mortality.
Other incidental insects found associated with
pifton include the tiger moth, Halisidota ingens, the
pifton sawfly, Zadiprion spp., pifton spindle gall
midge, Pinyonia edulicola, bark moths, Dioryctria
spp., and Vespamima spp., and the pifton pitch
nodule moth, Petrova arizonensis.
Insects of note associated with junipers include
the western cedar borer, Trachykele blondeli, and the
juniper twig pruner, Styloxus bicolor. The western
cedar borer is an aggressive pest of junipers and
Arizona cyprus in New Mexico. It belongs to the
Insects Associated with
Pinon-Juniper Woodlands
Insect activity in the pmon-juniper forest cover
type appears to be correlated with extended
periods of drought which predisposes large areas
of host type to attack During periods of average
rainfall, insect activity in the pmon-juniper type is
usually undetectable. Drought acts as a "trigger"
triggering ecological processes which eventually
leads to insect outbreaks that often extend over
thousands of acres of susceptible host type.
Probably the most important group of insects
associated with the pmon-juniper ecosystem are
the Ips bark beetles belonging to the family
Scolytidae. During extended periods of drought
Ips bark beetles (Ips confusus) often increase to
outbreak levels causing widespread tree mortality
on thousands of acres of host type. Mortality is
often patchy consisting of small groups of five to
ten fading trees. In some cases, entire viewsheds
and landscapes may be affected. Other Scolytid
bark beetles affecting pmon are the twig beetles.
1Forest Pest Management, New Mexico Zone, Southwestern
Region, USDA Forest Service.
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include swelling at infection sites, branch dieback,
and formation of witches' brooms.
Dwarf
mistletoes spread by shooting seeds from explosive
berries. True mistletoes are spread by birds that eat
the mistletoe berries. Seeds pass through the birds
unharmed and are spread in their feces.
Root disease infected trees are difficult to
diagnose since symptoms above ground can
resemble symptoms caused by other insect and
disease agents. Futhermore, little is known about
their affects within the pifton-juniper ecosystem.
Only recently have we observed and documented
amalleria root rot killing pifton pines in northern
New Mexico.
Armillaria root rot occurs in
expanding pockets, often with mortality at the
center. The entire crowns of infected pifton
saplings usually turns reddish-brown all at once.
Dieback, thinning foliage, or yellowing of the
crown is characteristic of older, infected pinon
trees. This disease spreads by means of spores and
rhizomorphs. When the fungus contacts the tree's
root or root collar, it penetrates the bark and enters
the living tissue. Cellulose is consumed leaving the
root light-colored and causing the tree's butt to rot.
buprestid beetle group also known as metallic or
flatheaded wood borers.
Unlike most other
buprestids, the western cedar borer will attack and
seriously injure or kill seemingly healthy trees.
Considerable damage is found in some juniper
stands; older, larger trees appear to be favored by
these beetles. The juniper twig beetle, also found
attacking junipers and Arizona cyprus causes twig
dieback This beetle belongs to the cerambycid
beetle group also known as roundheaded wood
borers.
Diseases Associated with
Pinon-Juniper Woodlands
Unlike insect outbreaks which are generally
cyclical and at times cause seemingly spectacular
damages and mortality across viewsheds and
landscapes, diseases are more insidious. That is
once a tree is infected with a disease pathogen, it
may take years before the symptoms appear and
several more years before the disease infected tree
dies. Mortality resulting from disease infections is
usually highest in young, immature trees.
Some diseases occurring in the pifton-juniper
woodlands include the mistletoes and root rots.
Mistletoes, Arceuthobium divaricatum on pifton and
Phoradendron juniperinun on juniper, are parasitic
plants that injure and eventually kill their woody
hosts by stealing water and essential nutrients.
Mistletoe plants vary in color from yellow to green
to red-green. Pifton pine dwarf mistletoe plants
consist of small conspicuous male and female
shoots approximately two to three inches in length
protruding through the bark of the infected
branches. True mistletoe plants very in length from
a few inches to several feet. Symptcms of infection
SUMMARY
In summary, there many insects and diseases
associated with the pinon-juniper woodlands.
Their presence does not mean they are a forest
pest. As we intensify our management activities
within the pifton-juniper woodlands, we will have
to monitor the impacts of resident insects and
diseases to determine (1) What kinds of damages
are occurring, (2) whether or not they are
significant, and (3) their impacts on management
objectives.
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