Yard
and Garden
April
18, 2015
Q. Our piñon trees are infested with scale (little black
specks turning the needles yellow). What can we do to save them?
Sylvia R.
Via University-Wide Extension web site
A.
Your piñon trees have a common pest of piñon, the piñon needle scale.
They rarely kill piñon trees quickly, but make them weak and susceptible to
other problems such as attack by borer insects and drought. These small
insects cause slow debilitation of trees by reducing the number of functional
needles on the trees. With fewer needles to capture sunlight and feed the
tree through photosynthesis, the trees become weaker over time.
The black specks you described on the needles are a waxy material the insect
makes to cover itself for protection. This waxy “house” protects the
insects from drying and from some predators. The yellowing needles you
described are the symptoms of their feeding on the needles. You will
notice that there is a tuft of green needles at the ends of the twigs with a
cluster of yellowed needles immediately behind the green needles, and usually
no needles on the twigs after that. The green needles are needles that
formed last year after the scale had infested the needles formed the previous
year. These infested needles will fall from the twigs this year and the
needles that formed last year will become infested this year. A small
tuft of new needles will form this year and maintain the appearance described
above.
The adult needle scale insects usually leave their protective coverings in late
winter and migrate down the tree. The female insects then lay their eggs
on the underside of branches, on the trunk, and in debris at the base of the
tree. A simple and effective way to reduce the effect of piñon needle
scale on your tree is to remove the eggs from the tree. The eggs are
contained in a dirty-white material that looks much like strands of yarn or
very think spider webbing on the underside of branches, the trunk, and the
debris. Using a broom to sweep most of this material from the tree or a
strong jet of water to wash it away removes the eggs and reduces the
infestation of the new needles as they form. If you can collect the egg
masses and destroy them, then there will be few new insects to infest the
needles that form this year.
If you want to have an even greater impact on the piñon needle scale
infestation you can watch for the newly hatched insects moving back up the tree
to settle down on the green needles that formed last year. These
“crawler” phase insects are very small and most easily detected by holding a
black or light colored piece of construction paper below the needles.
Then you can sharply strike the branch and needles above the paper with a
gloved hand (gloved to protect you from needles punctures). If you see
very small specks moving around on the paper after this test you have
discovered the crawlers. If you wish you may then spray the tree (on a
windless day) with insecticides labeled to control scale on ornamental
conifers. An insecticide containing the active ingredient acephate™ is
often effective when the crawlers are present. This is not an organic
material and if the eggs were sufficiently removed, treatment with insecticide
will not be essential. If you missed removing the eggs before they
hatched chemical treatment may be the only way to manage the problem this
year. However, since this insect is unlikely to kill the tree quickly,
you can wait and remove the egg masses as soon as they appear next year if you
prefer not to use chemicals.
An interesting note about this insect is that although they normally leave
their protective covering to deposit their eggs in the late winter, they were
observed out of the coverings and laying eggs in the autumn last year in Santa
Fe. So, egg mass removal can begin earlier in some years.
Send
your gardening questions to Yard and Garden, Attn: Dr. Curtis Smith, NMSU
Agricultural Science Center, 1036 Miller Rd. SW, Los Lunas, NM 87031. You may
also send to cwsmith@nmsu.edu or leave a message at https://www.facebook.com/NMSUExtExpStnPubs. Curtis W. Smith,
Ph.D., is an Extension Horticulture Specialist, retired from New Mexico State
University’s Cooperative Extension Service. NMSU and the U.S. Department
of Agriculture cooperating.
