Managing Aphid Outbreaks on Fruit Trees (and Other Plants)
Southwest Yard & Garden
Peach
tree stem infested with aphids is likely going to defoliate completely, but
this early in the growing season there’s a good chance it will bounce back and
be covered in new leaves in no time. Photo credits M. Thompson.
Question: What’s causing
our peach tree leaves to wither and curl up completely and should we also be
worried about our apricot trees nearby?
-
Lorraine J., Los
Lunas, NM
Answer:
Looking at the sample
you brought in, the leaf curl on your peach tree branches is pretty extreme,
and when I turned over and uncurled the leaves I found a ton of chubby green
aphids hiding underneath. Some of the leaves, especially at the tips, are
stunted and probably won’t fully expand after so much damage. Another aphid
clue is the shiny, sticky coating on many of the leaves. The sticky shellac is
called honeydew, which is a darling name for aphid excretion or – pardon my
French – poo.
In my first New Mexico summer I
was walking down Lomas Ave. in Albuquerque on the sidewalk in front of
UNM-Hospital, just minding my own business, when I felt a lovely mist falling
from the sky. It was brief, so I turned around to experience it again. I found
that this fine mist was coming from a street tree that I now know to be a
desert willow. I remember standing under the desert willow for a while,
enjoying the evaporative cooling effect, amazed at how a desert plant could be
so miraculous and kind. But that mist wasn’t water. It wasn’t until I took my
first entomology class years later that I learned the truth about honeydew.
Aphids of various species can be
expected each year on fruit trees and other landscape trees, shrubs, flowers,
and vines. These guys suck fluids from leaves and excrete a sugary liquid that attracts
ants and gets sticky and shiny as it coats the foliage.
Another
effect of the aphid’s piercing-sucking mouthparts and eating habits is that the
leaf can get deformed and start to curl up partially or entirely – especially
on stone fruit trees like peaches, apricots, cherries, etc. Here’s where the
task of controlling aphid populations gets tricky because they’re protected
inside the curled up leaves.
For home gardeners, I recommend keeping an eye out for shiny leaves, chubby aphids, and curled, deformed leaves throughout the season on all landscape plants. When you find some, don’t worry about eradicating the entire population – that’s not even possible. Just use a hose sprayer to power wash the visible aphid clusters off the plants’ leaves, buds, and stems. Once washed off, aphids tend to be disoriented and slow at getting all the way back up to the tender, succulent new growth that they love.
For home gardeners, I recommend keeping an eye out for shiny leaves, chubby aphids, and curled, deformed leaves throughout the season on all landscape plants. When you find some, don’t worry about eradicating the entire population – that’s not even possible. Just use a hose sprayer to power wash the visible aphid clusters off the plants’ leaves, buds, and stems. Once washed off, aphids tend to be disoriented and slow at getting all the way back up to the tender, succulent new growth that they love.
Also keep an eye out for
beneficial insects such as praying mantises, green lacewings, and ladybugs (more
formally known as lady beetles). Ladybugs in the larval stage are weird, stout,
black alligator-looking wigglers, often, but not always, with red markings. Insecticides might hurt the beneficial insect population before they’ve had a chance to work
their magic.
Praying mantis babies are particularly photogenic. Photo credits M. Thompson.
MORE RESOURCES:
I shared photos of the peach tree
stem with NMSU Extension Entomology Specialist and NMDA State Entomologist Dr. Carol
Sutherland. She pointed out the tiny white flaky bits as empty exoskeletons leftover
after some aphids molted. “As the weather warms, the blackish
aphids on stone fruits will likely fly away to alternate summer hosts. Green
peach aphids will remain on peach trees all year long. As populations get
large, winged aphids may be produced, but the tree will likely keep a residual
aphid population. Natural enemies should have a field day on these things.
Whether or not that will be good enough to control the pests to an acceptable
level is undetermined, but possible.” For more aphid info, check out the NMSU
Extension Guide “Aphids and Their Relatives” (https://aces.nmsu.edu/ces/plantclinic/documents/o-01-aphids.pdf).
Luckily, this early
in the season, foliar damage can be completely overcome by another flush of
growth and even badly defoliated fruit trees can rebound in just a few weeks. Give
the tree a leg-up by watering the entire root zone sufficiently to a depth of about
18-24 inches, depending on the size, and be sure to let the soil dry between
irrigations.
For more gardening information, including
decades of archived Southwest Yard & Garden columns, visit the NMSU
Extension Horticulture page (http://desertblooms.nmsu.edu/), follow us
on social media (@NMDesertBlooms), or contact
your County Extension office (https://aces.nmsu.edu/county).
Marisa Thompson, PhD, is the Extension
Horticulture Specialist for New Mexico State University and is based at the
Agricultural Science Center at Los Lunas.
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