I have noticed gumming coming from the hulls of almonds in several orchards. The gumming is clear, and can come from multiple points on the nuts. I have also been seeing it more on ‘Nonpareil’ than ‘Monterey’ or ‘Fritz.’
Initially suspected to be leaffooted plant bug, I think these issues are caused by another insect or are physiological. Once I cut into the nut, I do not find a small pin-hole from the bug’s proboscis, or feeding mouth part (Figure 2). Typically, if plant bug damage, a small pinhole can be observed from the surface to the shell (For an example of the pinhole, please see point 1:35 on this video). Even if it is leaffooted plant bug, the damage does not extend into the shell or kernel, and would have minimal effect on kernel development.
Gumming nuts should be checked to make sure that they have been damaged by leaffooted plant bug before spraying. There is more than one possibility to explain gumming nuts.
With that being said, perhaps I am missing something (or misdiagnosing). How much damage have you attributed to leaffooted plant bug?