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Southern Pecan Leaf Phylloxera
Warty-like bumps on pecan leaves can start popping
up in May. Resembling chickenpox, these bumps
are a result of a tiny aphid-like insect feeding on the
foliage of the pecan leaves. Once the feeding
damages the leaf tissue, the plant tries to
compartmentalize the wound. Then a gnarly
unattractive gall develops like a blister, in an effort
to limit the spread of the wound
this issue to get the populations to a manageable
level if possible.
Pecan phylloxera (Phylloxera devastatrix) insects feeding
within a gall (magnification = 30X).
Mark Arena ©2016 Specialty Crop Agent, Clemson Extension
Close up of leaves infected by Pecan phylloxera (Phylloxera
devastatrix).
Mark Arena ©2016 Specialty Crop Agent, Clemson Extension
The growth typically encapsulates this insect within
the gall. This response occurs for two reasons. First
to protect the leaf tissue and damage that has
occurred. Secondly, it provides a safe environment
for young insects to feed and develop. This is
known as a co-evolved response.
Even though the damage created by these insects is
unattractive and concerning at first glance, it
generally does not hurt the tree or impact nut
production. As with all pest and disease issues,
there needs to be an acceptable level of damage to
warrant action. Therefore, if there is only minor
damage, treatment may be unnecessary. However, if
the damage is extensive it may be best to treat for
Treatment must be timed appropriately in order to
be effective. The proper time to either treat or
prevent this issue from occurring is early in the
growing season when the leaves are just starting to
emerge. Proper treatment consists of spraying the
entire trunk and large branches with an insecticide
labeled for controlling aphids. The trunk is sprayed
because a majority of the eggs are laid in the cracks
and cervices of the bark. The eggs hatch in the
spring, when the leaves start to develop on the tree.
Therefore, by applying an insecticide at this time, a
majority of the young crawlers are terminated. It is
also recommended to make two to three additional
sprays as outlined on the label of the product used.
It is also important to clean up all the leaves on the
ground at the end of the year, since some eggs do
overwinter in the galls. These leaves need to be
properly disposed of to prevent additional
infestation by this insect. Currently, there is no
treatment available for this condition once it is
noticed and the leaves are damaged. Please
understand that treating this condition once it is
notice will have no benefit! You will only be
wasting your time and money. This condition needs
to be treated as noted under the Cultural and
Chemical Control sections of this publication!
The biggest challenge for homeowners is safely and
effectively treating a tree once it becomes large in
size. Currently, and for commercial production, the
primary method for treating these insects is by using
an insecticide that is sprayed onto the tree’s trunk
and large branches. For most homeowners this is
impractical and the cost associated with hiring a
reputable tree company to treat for this condition
would not be financially affordable. Also, most
homeowners are not willing to invest in the
equipment needed to properly spray the tree on their
own. Below are the cultural and chemical controls
that homeowner might consider.
Cultural Control: Keep the trees as healthy as
possible. Other stresses to the pecan tree should be
reduced, by fertilizing the tree in late February, and
liming in the fall according to a soil test report.
Additionally, pecan trees should be watered weekly
during periods of drought for the best development
of the pecan nut crop. Rake and burn or dispose of
fallen leaves in autumn.
Chemical Control: No effective control of
phylloxera is available once the galls are present.
Sprayed insecticides will not reach the insects
inside the galls, and systemic insecticides will
usually not reach high enough concentrations in the
leaf galls to kill the insects. Commercially, pecans
are sprayed one or two times in the spring shortly
after bud break when the eggs hatch and the small
insects are crawling to the developing leaf buds.
Homeowners could attempt this if the pecan trees
are small, using carbaryl with two applications at 7
to 10 days apart. Follow label directions for use.
However, it is impossible for a homeowner to spray
a large tree and get good coverage in a safe manner.
If Southern pecan leaf phylloxera severely damaged
the pecan the previous year, a homeowner can spray
a 4% horticultural oil solution (10 tablespoons oil
per gallon water) to thoroughly wet the trunk, limbs
and smaller branches before bud break (before new
spring growth) during the winter or early spring.
The winter is spent in the egg stage on the bark in
cracks and crevices, and in the crevices of old galls
on fallen leaves. This is a much safer approach to
control the pest, and the oil spray will smother the
eggs and any nymphs that have hatched.
Prepared by Mark Arena, Specialty Crop Agent, Clemson Extension,
Clemson University Cooperative Extension Service. 07/16.
This information is supplied with the understanding that no
discrimination is intended and no endorsement of brand names or
registered trademarks by the Clemson University Cooperative
Extension Service is implied, nor is any discrimination intended by
the exclusion of products or manufacturers not named. All
recommendations are for South Carolina conditions and may not
apply to other areas. Use pesticides only according to the directions
on the label. All recommendations for pesticide use are for South
Carolina only and were legal at the time of publication, but the status
of registration and use patterns are subject to change by action of
state and federal regulatory agencies. Follow all directions,
precautions and restrictions that are listed.
The Clemson University Cooperative Extension Service
offers its programs to people of all ages, regardless of race, color, sex, religion, national origin, disability, political beliefs, sexual orientation, marital or family status and is an equal opportunity employer.
Clemson University Cooperating with U.S. Department of Agriculture, South Carolina Counties, Extension Service, Clemson, South Carolina. Issued in Furtherance of Cooperative Extension Work in
Agriculture and Home Economics, Acts of May 8 and June 30, 1914
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