Sometimes orchards I’ve visited in past years come back to haunt me. Recently I received a call from a PCA – when I answered the phone, he started the conversation with: “It’s doing it again.”

Each year, about this time, Winters almonds in this particular orchard begin gumming. Photo credit: D. Lightle

This particular orchard is about 5 years old, situated on a gravelly loam soil, and is planted with Butte, Nonpareil & Winters on Krymsk 86. The gumming symptoms are variety specific, occurring almost exclusively on the Winters nuts. When nuts are cut open, they have an amber gel in place of normal kernel development.

Amber gel fills where the kernel should be developing. Photo credit: D. Lightle

Hull samples taken at harvest last year had about 30ppm boron – well below the 80ppm considered the deficiency threshold. The grower applied boron through the irrigation system this spring to help remedy the situation, and we were disappointed to still see so many gummy kernels.

We sampled hulls a couple weeks ago and sent them off for a boron analysis. Almond trees continue to accumulate boron throughout the growing season, so boron levels from May are not directly comparable to the thresholds established for harvest samples. However, they are still useful to determine whether we had increased the boron levels at all from last year, as well as provide information on whether we were approaching toxicity with the boron applied earlier this year.

Amber gel fills where the kernel should be developing. Photo credit: D. Lightle.

The samples came back in the 50ppm range. The good news is that we have increased the boron levels over last year; however, the low readings also explain why we still saw so much gumming. Because we are not approaching toxicity, we will likely go in with more boron this season.