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Pockets of Moderate Drought Persist
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Bouts of severe weather that included tornados, caused intermittent
flooding, hail and strong winds in many areas across the state. 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. Reports of downed limbs and entire trees have caused
numerous instances of property damage. The Missouri river has reached peek moderate flooding that
almost rivals the flood of 2019 affecting most counties along the eastern line of Nebraska.
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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Japanese Beetle Emergence
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Japanese beetles are an introduced insect, coming to the United States in
the early 1900's. The larvae (grubs) feed on the roots of turf and the adults feed on over 300
species of plants (including corn and soybeans) creating a lacey pattern on leaf tissue. This insect
can be quite a nuisance, especially on linden, cherry, crabapple, buckthorn and roses.
Photo Courtesy of digitaldiagnostics.unl.edu
Lawns can be checked for grub activity. If there are yellow areas in the
turf, grass can be pulled up close to the edge of the yellowing and grubs will be present in the
soil. Usually, grubs will be actively feeding on turf roots in late May and June before pupating into
adults. Adults will feed, mate and lay eggs through August.
Management of the insect can sometimes be difficult. Pheromone traps are not a good management tool
as the traps have been shown to attract more beetles to the area. Hand picking and disposal is an
option, planting certain plants like chives, garlic and catnip will deter the beetle in rose beds and
gardens. Pesticides can be used as either a soil drench to control the grub or sprayed on the foliage
to discourage feeding of plant tissue by the adult. Be sure to check label guidelines as most
products cannot be used on lindens or basswoods (Tilia sp.)
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Photo Courtesy of Joel Floyd, USDA APHIS
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Neurotoma inconspicua larva
Photos Courtesy of Toby Burnham
As we showcased in our May Monthly Report, 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.
Web spinning sawfly are housed in a smaller family with 75 species represented in North America.
Pupation happens in the spring. Adult flies emerge, laying eggs that hatch within 5-7 days.
Larvae live in the webbing they spin around the leaf tissue and branches of their hosts. Feeding
lasts for 2-4 weeks. The larva then drop to the ground, bury themselves and wait out the
winter.
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Photo courtesy of Toby
Burnham
Webbing on a plum from web spinning
sawfly - notice the missing leaf tissue and left over debris.
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This web spinning sawfly infests plum and sand cherry bushes
specifically.
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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Bob Oakes, USDA Forest Service,
Bugwood.org
Red turpentine beetle larvae feed on the inner bark of pine trees
weakened by drought, fire or other stress. Pitch masses are noticeable on the lower 8
ft. of trunk. A hole is apparent in the pitch mass and this hole is used to push red frass
out of the beetle’s chamber. Red turpentine beetle predisposes the tree to attack from other
beetles. Insecticides labeled for bark beetles can be used on the lower 8 ft. of the tree as a
preventative but will not prevent other insect attacks or tree decline from stress.
Red Turpentine Beetle Larva
Donald Owen, California Department of Forestry & Fire Prevention, Bugwood.org
Red Turpentine Beetle Adults are 1/4"-3/8" Long
Photo Courtesy of Joseph Berger, Bugwood.org
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European Elm Scale on Elm Branch in McCook, NE
Photo Courtesy of Laurie Stepanik
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.
European elm scale is a soft scale with a summer hatch that lasts for several weeks. The
adult female at this time will be reddish brown to grey in color, surrounded by a white ring of fuzz
and stationed sessile on elm bark (pictured above). The crawlers, shown below are very small and
yellow. Crawlers can be found feeding on the underside of elm leaves once they have
emerged. Feeding and development continues through August and September.
Photo Courtesy of Laurie Stepanik
In high numbers, this scale can cause leaf yellowing, defoliation and if infestations continue
yearly, branch dieback. Continuous yearly chemical control of systemic neonicotinoids and
imidachloprid over time can result in resistant populations. Overhead sprays of insecticides
may also lower the populations of beneficial insects and other predators that feed on scale. If
populations are severe, using a combination of dormant oil in the fall and/or spring with a systemic
insecticide of an insect growth regulator like pyriproxyfen may help in lowering scale
populations and have little impact on beneficial predators. Keeping trees watered
during drought and lowering other stressors will also help in scale attack.
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Compiled by Jennifer Morris, Forest Health
Specialist
jmorris12@unl.edu
402-326-7276
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