It is interesting that for the most part, the damage was exclusively on the Monterey variety, with not a scale to be found on adjacent Nonpareil or other pollinizer trees.
Some growers with the Avalon variety reported seeing walnut scale on that variety. This year, I am seeing it affect the Independence variety to the point where it will require treatments.
Take A Closer Look
Close examination of the scale activity on the young wood and scaffolds will show a very high percentage of parasitism. It appears that this should keep the damage at a low enough level that sprays are not necessary. This is not the case. If the bark is pealed back on heavily infested limbs or scaffolds, it will reveal injury to cambial tissues (see photo) that may not appear that serious.
However, when the warm temperatures and high transpiration periods occur prior to harvest, many of these limbs suddenly collapse and die.
Growers with bearing blocks of Independence, Monterey, or Avalon should keep an eye out for this limb dieback in the lower portion of the canopy. Actually, treatments should be applied prior to the dieback since this is a loss of potential producing wood.
Control measures can be as simple as oil treatments on low populations, a dormant organophosphate, or a delayed-dormant or spring application of an insect growth regulator such as pyriproxyfen or buprofezin.