March/April 2023 - 12

Gill's mealybug
in pistachio
Close monitoring and
smart rotations are key
Gill's mealybug nymphs on a pistachio green tip
in March. Photos: David Haviland, University of California
ill's mealybug is a persistent pest of pistachios,
feeding on nut clusters and leaving behind a mess in
the form of honeydew, affecting nut marketability.
The honeydew serves as a substrate for black sooty molds
that stain the hulls, but not the shells underneath. Because
the insects suck up sugars that would otherwise enhance
nut growth, the nuts may be smaller and less likely to split
when they should. These mealybugs mainly attack the nut
hulls, so they're not found on pre-bearing or male trees.
Young California pistachio orchards thus go through
a period where they are not infested. The mealybugs
eventually appear and build up over time, but typically they
can be maintained at a low level with good management.
In California, winter monitoring for Gill's mealybug
would reveal dead adult females on the trunks and
branches. The females possess two wide tails, distinguishing
them from grape mealybugs, which feature four slender
tails, two short and two long. Also, when poked, grape
mealybugs exude a red liquid, but Gill's mealybug does
not. The grape mealybug does not require treatment, so
it is important to determine the species as part of the pest
management program.
Spots of heavy infestation of the dead mealybug adults in
the winter can be flagged for careful checking in the spring.
Early instar nymphs are also present in winter, but their
tiny size and their behavior of hiding in cracks render them
invisible in winter.
" You don't care about (the dead mealybugs). What you
care about is the babies that they made, that are teeny,
tiny, first instars, tucked away in cracks and crevices, so
you're never going to find them, " said David Haviland,
farm advisor, University of California Cooperative
Extension, during a 2020 presentation. " I shouldn't say,
'never going to find them,' because you are going to find
them - around March. "
In March, the nymphs crawl to the buds, where they
are visible on and near the new green tips. By late April,
adult females make little " cotton candy " nests. By the

March/April 2023

Table of Contents for the Digital Edition of March/April 2023

March/April 2023 - 1
March/April 2023 - 2
March/April 2023 - 3
March/April 2023 - 4
March/April 2023 - 5
March/April 2023 - 6
March/April 2023 - 7
March/April 2023 - 8
March/April 2023 - 9
March/April 2023 - 10
March/April 2023 - 11
March/April 2023 - 12
March/April 2023 - 13
March/April 2023 - 14
March/April 2023 - 15
March/April 2023 - 16
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March/April 2023 - 25
March/April 2023 - 26
March/April 2023 - 27
March/April 2023 - 28