It may well be. During the summer, spots with no stage 1 trees are not likely to expand because attractants are no longer present. And spots with only stage 3 trees since beetles have already left need no control at all. Check to see if the spot is expanding in more than one direction.
Large spots can have more than one active head.
Determine the number of stage 1 and 2 trees. For large spots that have more than 50 trees, it is not necessary to examine each tree. Just walk the boundaries and estimate the number of these trees in the spot. A 10-factor prism is useful for this purpose. Using the Control Priority Guide from the next section of this handbook, determine the control priority for the spot.