April 2021 - 16

PLANT HEALTH
dr. bugs
BY RAYMOND A. CLOYD
Tips on Managing Mealybugs
Question: What are your recommendations regarding the management of
mealybugs in greenhouse production systems?
Answer: The question you ask is very
appropriate and timely. In general, the
common mealybug species
encountered in greenhouse
production systems is the citrus
mealybug, Planococcus citri.
Citrus mealybugs use their
Raymond A. Cloyd
is professor and
Extension specialist
in horticultural
entomology/
plant protection
at Kansas State
University. He
can be reached at
rcloyd@ksu.edu.
piercing-sucking mouthparts to
withdraw plant fluids from the
vascular tissues or phloem sieve
tubes. During feeding, citrus
mealybugs excrete honeydew, a
clear, sticky liquid that serves as
a substrate for black sooty mold.
Citrus mealybug can disperse
among greenhouse-grown
horticultural crops when plant
foliage is touching. One adult
female citrus mealybug can lay over
400 eggs during her lifetime. Therefore,
managing citrus mealybugs by killing the
nymphs (crawlers) before they develop into
adults (males and females) is important.
Insecticides are primarily used to
suppress citrus mealybug populations in
greenhouse production systems. So, why
are citrus mealybugs so difficult to manage
with insecticides? First, in our research at
Kansas State University, we have found
that systemic insecticides applied to the
growing medium as a drench or granule
are not effective (i.e., based on the level of
mortality), in suppressing citrus mealybug
populations under greenhouse conditions
to prevent plant damage. Therefore, spray
applications of contact insecticides are
required. However, contact insecticides
may have limited effectiveness against
citrus mealybugs due to the following:
* The later instars and adults have
a hydrophobic (water-repelling)
waxy covering that protects citrus
mealybugs from exposure to
insecticide spray residues.
* There may be difficulty in obtaining
thorough coverage with insecticide
spray applications of all above14
APRIL 2021 GPNMAG.COM
Contact insecticides are most effective
against the early-instar nymphs because
they do not have a hydrophobic waxy
covering. However, applying sufficient
spray volumes to obtain thorough
coverage of all plant parts including:
the underside and upper side of leaves,
stems, and applying contact insecticides
frequently, are essential in managing
citrus mealybug populations.
In our research, we have found that
Citrus mealybugs feeding on stem of
poinsettia.
Mealybugs feeding on plant stem.
ground plant parts (leaves and
stems) where citrus mealybugs feed,
especially on large plants.
* Citrus mealybugs reside in protected
or hidden areas on plants that can
reduce exposure of individuals
(nymphs and adults) to insecticide
spray applications.
* Overlapping generations with an
age structure that consists of all life
stages (eggs, nymphs and adults),
can be present simultaneously.
spray applications of acetamiprid
(TriStar) to be most effective against the
citrus mealybug. Nonetheless, highvolume
sprays and repeat applications
are necessary. Furthermore, based
on our research, the addition of a
surfactant to an insecticide solution may
not enhance the efficacy of the spray
application.
A major problem associated with
using contact insecticides to suppress
citrus mealybug populations is that
high mortality (>90%) is required. The
reason is that if just one adult female
escapes exposure from insecticide
spray applications then the female will
lay her compliment of eggs (oviposit),
which will lead to 300 to 600 nymphs
emerging (eclosing) from the eggs and
subsequently feeding on a plant.
In general, if a plant is 50% infested
with citrus mealybugs, which will depend
on plant size, then the plant should be
disposed of immediately. Therefore, it is
important to scout crops at least twice
per week, especially those susceptible to
citrus mealybug, to detect infestations
early enough so that insecticides can be
applied accordingly.
For more information on how to
manage citrus mealybugs in greenhouse
production systems, consult the
following extension publication:
Mealybug: Management in Greenhouses
and Nurseries (https://bookstore.ksre.
ksu.edu/pubs/mf3001.pdf).
https://www.bookstore.ksre http://www.ksu.edu/pubs/mf3001.pdf http://www.GPNMAG.COM
April 2021

Table of Contents for the Digital Edition of April 2021
