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Drought Continues in South Eastern
Nebraska
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Drought conditions still persist in the SE central region of Nebraska and soil
moisture is very low around the Lincoln and surrounding areas. Bouts of severe weather that included tornados and derechos this month caused
intermittent flooding, hail and strong winds. Stem diseases, like cystospora canker, diplodia tip
blight and fire blight can become a problem following these types of events if susceptible trees have
sustained damage. Trees, whose roots have been underwater for extended periods of time, can
develop root rot and root stability may be in question after flooding. A great article written by
Graham Herbst, Eastern Community Forester, explains how to exam and care for trees after
flooding. You can review Graham's article here:
https://nfs.unl.edu/publications/flooded-trees
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Ash
Sawfly Larva on Ash Leaf, Lincoln NE
Photo Courtesy of Laurie Stepanek
Sawflies are quite numerous with roughly over 1,000 species represented
in 10 families. The insect gets its name by its saw-like ovipositor, an organ shaped tube(s)
used for egg laying. Adult sawflies can look like flies but are more closely related to bees and
wasps. Most sawflies have one generation per year consisting of egg, larva, pupa and an adult
stage. Though the larva looks similar to caterpillars, several differences can be noted
for identification. Sawfly larvae have 6 or more pairs of prolegs without gripping hooks behind
3 traditional pairs of legs, while moth and butterfly larvae have 2-5 pairs of prolegs with gripping
hooks. Sawfly larvae typically are spineless, hairless and consistently have a head segment
distinct from the body.
Commonly in Nebraska we find brown headed & black headed ash sawfly, European pine sawfly, and
yellow headed spruce sawfly, oak sawfly, among others. Defoliators of deciduous trees are more
of a nuisance pest in our state. The ash sawfly for instance, in a high population year, can
inundate ash trees, dropping fecal matter in abundance and alarming homeowners during the
invasion.
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Brown headed ash sawfly larva crawling around and up an ash
tree
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Brown headed ash sawfly adult
Courtesy of bugguide.net
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European Pine Sawfly Larva
Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org
European pine sawfly larva that feed on evergreen needles can congregate in
high numbers, becoming destructive, and defoliating entire branches of Austrian, Scotch, mugo, jack or
ponderosa pine trees.
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Photo courtesy of Eric
Berg
European sawfly larva group on pine
branch, notice the needles have been eaten.
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Control of sawflies is usually not necessary if populations are in small
numbers. Healthy trees, especially deciduous trees, can handle slight defoliation and a few
larvae can be picked off a small tree/shrub easily. If high numbers are present and feeding is
expected to be severe, treating with an insecticide may be warranted. Insecticides will work best
when the larvae are small. Several products on the market will control sawflies. Look for
active ingredients of permethrin, bifenthrin, acephate or insecticidal soap/oils.
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Elm Zig Zag Sawfly - Is It On It's Way?
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The elm zig zag sawfly (EZS) is a non-native, invasive pest from Asia that was discovered in
Virginia in 2021. Since that time, it has been found in 7 additional states -
Pennsylvania, North Carolina, Maryland, New York, Vermont, Massachusetts, &
Ohio.
This sawfly can produce up to 6 generations in a year and can defoliate elm trees rather
quickly. Slippery elm, Siberian elm, American elm, Chinese elm and elm hybrids are all
susceptible to infestations.
This sawfly is parthenogenetic, meaning that no males have ever been recorded to exist.
Each generation is female, produced by asexual reproduction. The adults can fly up
to roughly 55 miles per year.
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Photo by Matt Bertone, NC State University
Pictured above is an EZS larva. Notice the lime green coloration with
dark banding on the head. The 2nd and 3rd leg have noticable "T" shaped dark
markings.
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The larvae can produce one of two types of cocoons before pupation. One that looks
like spun gold sugar with webbing attaching it to the leaf (upper left). This cocoon
holds a larva that will pupate in the summer months. The other cocoon is a spun shell
(upper right) and more so found after defoliation has occurred in the late summer months and
found down on the ground or on other surfaces - cars, homes etc. This second type
of cocoon house larva that will pupate the next year.
Photos by Matt Bertone, NC State University
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The adult (above left) is black in color with 3 pairs of light-colored legs. The EZS
gets its name by the pattern left after larva feed in-between leaf veins on the elm leaf
(above right). Feeding can by quite devastating with multiple generations in a
year.
EZS has not been found in Nebraska at this time. Contact FH for more information or if
you suspect you have found EZS.
Adult Photo by Gyorgy Csoka, Hungary Forest Research
Institute, Bugwood.org
Leaf Pattern Photo by Tom Macy, Ohio DNR Division of Forestry, Bugwood.org
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Gray’s Creek CA, 13 August 2023. Owen Clarkin photo
All leaf tissue except the midrib and some vein tissues have been consumed
by EZS on this elm branch.
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Venturia Leaf Spot & Shoot Blight of
Aspen
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This fungal disease infects emerging leaves and shoots of aspen by
windblown spores in the spring. Once infection occurs, the leaves develop blackened and distorted
leaf tissue. The fungus moves to expanding shoots where cankers form, causing the shoots to
discolor and curl. These infected shoots are a source for spore development the following year.
Continued infection on aspen may cause stunted growth, giving the tree a shrub like appearance and also
weaken the tree.
Wet springs followed by wet summers increase infection rates. Pruning out infected shoots and
thinning dense groves will help. If fungicide applications are necessary, spray fungicides
labeled for Venturia sp. in the spring as new leaves/shoots emerge to help protect the shoots from
infection. Look for fungicides with an active ingredient of myclobutanil, mancozeb, or copper among
others.
Photo submitted by Terry Morris
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Rust projections on infected
apples
Photo by Rebekah D. Wallace University of Georgia, Bugwood.org
Cedar-apple rust and Cedar hawthorn rust diseases require 2 hosts to
complete their life cycle. The fungus overwinters on juniper or eastern redcedar trees in the winter.
The spores are released in the spring from gelatinous orange galls on junipers or cedars and land on
apple, crabapple and other susceptible deciduous trees. After infecting their growing season hosts,
spores are released in late summer to infect their Juniperus host, completing the life cycle. If severe
defoliation is occurring each year, an application of fungicide labeled for rust at bud break and 2
additional applications 7-14 days apart will help to lower the effects of the disease.
Rust Fruiting Bodies on
Cedar
Photo by Terry S. Price, Georgia Forestry Commission,
Bugwood.org
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Pine needle scale infestation on pine sp.
Photo by USDA Forest Service - Coer d'Alene Field Office, Bugwood.org
Scale insects are a diverse and numerous group of insects. Scales have sucking mouthparts that suck
nutrients out of tree tissue. In some cases, damage is minimal and chemical treatments are not
necessary. Often natural predators and parasites control the populations of the insects but sometimes
scales can heavily infest a tree to the point of dieback, creating the need for more aggressive
control.
Scales are classified into two categories - soft scales and armored scales. Soft scales feed
from the phloem tissue of plants, causing them to excrete honeydew, a waste product highly sweet that
attracts other insects and mold. Soft scales also can develop a waxy layer over their body protecting
them from predation. Armored scales feed from mesophyll cells of plants, do not excrete
honeydew and develop a hard, detachable outer shell for protection.
Pine needle scale is an armored scale that can infest may species of evergreens. In Nebraska it
commonly infests pines, namely white, mugo and Austrian. They also can infest spruce and
fir.
Adult pine needle scale
Photo by Robert J. Bauenfeind, Kansas State University, Bugwood.org
Pine needle scale has a first-generation spring hatch roughly around the time of lilac bloom, where
immature scales are called the "crawler" stage. The crawlers emerge from eggs that have been
protected by the adult female scale covering over the winter. Armored scale crawlers are only
mobile until their first molt. They lose their legs and become immobile. This generation
develops into adults, mate in July, and lay eggs for the second generation.
Immature crawlers are small, oval shaped and range from rusty red to
purple in color
Photo by Howard Russell, MSU Diagnostic Services
If high numbers of scale are present, needle browning, needle loss and branch dieback can
occur. Oils or traditional insecticides can be applied at the crawler stage to lower populations
in either the 1st or 2nd generation. Traditional insecticides as overhead sprays during the adult
stage are not as effective due to the protection of the adult scales outer shell.
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Compiled by Jennifer Morris, Forest Health
Specialist
jmorris12@unl.edu
402-326-7276
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