Since the fungus causes dieback of shoots and fruiting wood, Doll says growers can see reduced yields in future years.

Unlike many other pests, hull rot does not affect the quality of almond kernels, he says. It increases the number of stick tights which are not harvested which reduces yields.

Doll says stuck nuts pose a challenge for winter orchard sanitation crews removing the mummies.

Over the years, UC has developed an integrated approach to minimize almond hull rot which includes matching nitrogen rates to anticipated yields and inducing moderate irrigation stress during hull split.

The goal is to temporarily modify the microclimate around each nut to make it less conducive for the fungi.

Machado said, “The University of California says nitrogen and irrigation management are key pieces to the puzzle in minimizing hull rot. It all boils down to humidity and the microclimate in the split hull. When you have humidity levels like we did this summer, it will be tough to mitigate."

Research led by University of California, Riverside plant pathologist Jim Adaskaveg also has shown that a single application of a sterol inhibitor or strobilurin fungicide timed with the Navel orangeworm hull-split insecticide spray can reduce Rhizopus-caused hull rot from 60-70 percent.

Doll adds that fungicide is not promoted as a stand-alone hull rot treatment and instead should be part of an integrated approach.

Even many growers who followed a multi-faceted course this season had high incidents of hull rot due to high ambient humidity, which Doll says was 10-15 percent above average for several weeks.

“I've seen farmers who have never had hull rot have problems who have problems this year," Doll said.

Machado says Blue Diamond field staff has reported hull rot more in the Nonpareil variety than in other types, which he attributed to that variety's stage of hull split during the monsoonal period.

“The Nonpareil variety split the most during the high humidity period,” he said. “I was in an orchard with Carmel (Aug. 11) and they weren't even ‘smiling.’ It just depends on the weather conditions in the orchard when splitting occurs.”

Machado says typically if the hull seal is tight then you there is not a problem. If the hull is split and dried out, there is usually not a problem.