Ask Your PCA: What are ways to keep NOW levels in check in pistachios?

By Justin Nay
Integral Ag Services, Durham

Pistachio trees are alternate bearing, with higher yields in “on” years followed by lower yields during “off” years. 2025 represents an “on” year, so most growers are expected to have a good crop. In high-yielding years, all varieties tend to produce more premature splits of the hull and shell before harvest, exposing the kernel to potential damage.  

Early splits are a bigger problem for the Kerman pistachio variety because it is harvested later—in September. This is less of a problem for the Lost Hills and Golden Hills varieties, but it still happens. There could also be navel orangeworm, or NOW, damage. Early splits allow NOW access to the nuts, so monitoring early splits is important. 

Each variety has a different susceptibility for early splits at different times of the year, depending on the crop. Early splits can start showing up the last week of June but typically don’t appear until the first two weeks of July, so assessing early splits mid-July through early August can help keep NOW levels in check. 

As the kernels size and the hulls split open, the problem can progressively get worse. NOW are attracted to the nuts once the hulls split, and this provides an entry for the larvae to cause damage. 

There are different NOW flights, and depending on how those flights overlap with early splits and their abundance, NOW can cycle on those early splits. This means they can complete one generation before harvest and growers could be dealing with a very large number of NOW after hull slip, when the hull separates from the shell, signaling nuts are ready for harvest. 

When early splits happen and the flight lines up, if there are too many early splits and too many moths, growers should sanitize again by sweeping, blowing and shredding the mummy nuts. That’s the best way to reduce the pressure in conjunction with spraying.