I have had several calls and sample submissions in regards to kernel gumming on ‘Nonpareil’ kernels. In one case, as much as 5% of the kernels have been rejected. Many farmers and consultants are speculating that it is leaf footed plant bug (LFPB) damage. I am unsure of the exact cause, but the observed symptoms do not always match LFPB.
Observations of damage include shriveled kernels that usually have an area that is sunken and covered in a hardened gum (Figure 1). The shrunken area generally tends to be on the wide end of the nut. It is within this area that the gumming appears to originate. On some nuts, there are darkened spots that indicate the potential LFPB feeding, but in 80-85% of the cases, this is not present.
Pictures were sent to UC IPM Advisor David Haviland in Kern County, and he indicated that some LFPB damage is present, but he thought that most of the problems appear to be another issue (Figure 2) (A nice picture of LFPB kernel damage progression can be found here). Hull analysis for boron was completed in some of the orchards and results do not indicate a severe deficiency or toxicity. I am unaware of any disease that could cause this type of symptom.
So, with all of that written – does anybody have an idea? I am beginning to think it might be a physiological response to conditions experienced this past spring or perhaps increasing salinity, alkalinity issues. Widespread damage experienced across a region would support this hypothesis, just as more localized damage would indicate some type of pest or disease.
I have found this within three of my test plots (Livingston, Atwater, and Le Grand) this past year and I have received samples from the Turlock and Los Banos area. Roger Duncan has received a few calls on it as well.
I would appreciate any information that you are willing to share.