Nebraska's Forest Health Report June 2024

Nebraska's Forest Health Report June 2024
Nebraska's Forest Health Report June 2024
Pockets of Moderate Drought Persist 

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:
Japanese Beetle Emergence
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
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.)

Photo Courtesy of Joel Floyd, USDA APHIS
Plum Web Spinning Sawfly
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.

Photo courtesy of Toby Burnham
Webbing on a plum from web spinning sawfly - notice the missing leaf tissue and left over debris.
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. 
Red Turpentine Beetle
Bob Oakes, USDA Forest Service,
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,

Red Turpentine Beetle Adults are 1/4"-3/8" Long
Photo Courtesy of Joseph Berger,
European Elm Scale
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. 
Compiled by Jennifer Morris, Forest Health Specialist
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