He said it is important to reduce the amount of nitrogen and water during hull split, thereby cutting growth that might be more conducive to infection.

Some varieties, including Nonpareil, are more susceptible to hull rot, Doll said.

He recommends creating “a water deficit” before the nut begins to split, dropping applications by about 50 percent for a week.

If wilting occurs, he advises a second week at 70 percent of accustomed levels.

Then, he said, the grower should go back to full irrigation in order to prevent formation of an abscission layer that can lead to “stick-tights” and to avoid drawing moisture out of the kernel, which would mean lost weight.

Rolinda grower Nick Nazaroff said hull rot “nearly destroyed” his orchard, but he has gotten the problem under control by switching from irrigating all rows, starting in mid-May, to every other row.

Fungicides can be used on hull rot, but Doll said different products should be rotated to avoid developing resistance to sprays. He said the products do not need to be costly.

Most common in the southern San Joaquin Valley is the Rhizopus pathogen, he said, calling for application of a fungicide at hull split. It can be applied at the same time as products used to control navel orange worm, Doll said.

To the north, it’s more common to encounter a Monilinea pathogen, which is best treated in mid-May, Doll said.



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