Figure 3.-SPB spot expanding in several directions.
The major purpose of SPB control programs during the summer months is
to reduce timber losses by locating and treating expanding infestations.
Spots which are no longer expanding are soon abandoned by the beetles
and have little need for control. To assist ground crews, you need to
distinguish SPB spots showing visible symptoms of expansion from other
spots likely to become inactive.
But how can you tell from the air if a spot will expand? Yellow crowns
are the most useful clue. An expanding spot will have at least some yellow
crowns. Rapidly expanding spots contain as many yellow-crowned trees as
red ones. The location of the yellow-crowned trees within the spot marks
the path of its spread, which may be in one direction (see fig. 1), or
in several (fig. 3). When a spot becomes inactive, it will no longer have
such trees (fig. 4). For control purposes, you do not need to report spots
without yellow crowns.
||During SPB outbreaks, spots may
range in size from one to several hundred trees. As a general rule, the
larger a SPB spot appears from the air, the more likely it is to grow. You
can greatly aid control operations by reporting only spots with a total
of five or more red- and yellow-crowned trees. Spots with fewer than five
trees are not likely to expand and will often become inactive during the
summer (fig. 5). This minimum will also eliminate recording many small Ips
and black turpentine beetle spots, which are less prone to cause economic
losses. True, you may overlook a few expanding SPB spots by using this practice,
but these will be recorded later if they exceed five trees in size. During
severe beetle outbreaks, forest managers may make the minimum reporting
size larger than five trees if workloads of ground check crews become too
You should estimate the size of each spot reported. Two methods exist
for such estimates. one, recording total number of dead and dying trees,
which is indicative of the amount of salvageable timber; or two, noting
only the number of red- and yellow-crowned trees, but not those having
lost most or all of their foliage. This second method provides a better
measure of trees that still contain beetles. Before selecting one method
over the other, check the survey policy of your organization. And be sure
that ground crews know which estimating system you use.