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Nebraska's Forest Health Report

July 2019
Verticillium Wilt
Symptoms of Verticillium wilt are now becoming apparent in infected trees in the form of wilting and dying branches. This is most often seen in species of maple, elm, catalpa, and magnolia. The disease is caused by a fungal pathogen that lies dormant in the soil, often in pockets. If roots of a susceptible tree run into this fungus, it may infect the plant, often causing dieback on branches. Certain infections may also be chronic and lead to a slow dieback. Infested tree tissue may or may not show staining of the vascular tissues.

Unfortunately, there is no cure for this disease. Trees showing symptoms can be pruned back and properly mulched and watered to improve tree health. Remember to sterilize all tools used for pruning after each cut. If the tree dies or removal is desired, it is advised to plant a resistant species in its place. Resistant species include oak, willow, honeylocust, walnut, and linden among others. 
Verticillium wilt is often seen on Norway Maples, presenting as sudden dieback as vascular tissues become blocked.
Zebra Swallowtail Butterflies
Zebra Swallowtails (Eurytides marcellus), are striking butterflies that are currently flying in parts of Southeastern Nebraska. The larvae of these butterflies are unique in that they feed only on Paw-paw (Asimina triloba). While they will create some small holes in the leaves, they rarely cause any serious damage and are generally not regarded as pests. Larvae are striped, usually either green or black, with the area around the head being wider than the rest of the body. Nebraska is on the edge of this butterfly’s native range, so be sure to be on the lookout for it!
Clockwise from upper left: Egg, 1st instar black larva, adult feeding, 2nd instar yellow/green larva

Adult Photo Credit: Pennsylvania DCNR - Forestry, Bugwood.org
Hackberry Tatters 
Recently, damage was noticed on the leaves of this hackberry tree near Wayne NE. Damage closely resembles leaf tatters, a condition thought to be linked with herbicide but is not yet fully understood. Herbicides suspected of causing tatters include those with the active ingredients acetochlor, metolachlor, and dimethenamid. 

The cupping and curling of leaves seen on hackberry and many other trees is due to a different class of herbicides, the growth regulator herbicides such as dicamba and 2, 4-D.
Left: Hackberry leaves showing tatters possibly caused by herbicide
Right: Hackberry showing damage more typical of a growth regulator herbicide
Cedar Bark Beetle
Cedar bark beetles, (Phloeosinus spp.) are small beetles approximately 1/8 inch long which feed on the inner bark of cedar trees. Under normal conditions they usually cause little damage to redcedar, and their presence goes unnoticed. However, when large numbers of trees are stressed they can reach high population levels.

Clearing redcedar from pastures and leaving the cut trees in piles can attract large numbers of beetles, which will lay eggs in the newly dead trees. The following spring, new beetles will emerge and search for new trees to feed on, likely in the form of desirable windbreak trees. Adult feeding causes browning in tips. If trees are stressed or populations are too high, larval feeding on the main stem may lead to dieback or death. If clearing large numbers of cedars from the landscape consider burning the trees before June when adults will emerge and begin to feed.  
Left: Dead branch tips and the entrance hole where the adult beetle is feeding
Right: Main trunk with exit holes where larvae have damaged the tree
Stag Beetle Larvae
These beetle larvae (most likely stag beetle Family: Lucanidae) were found inside a recently cut ash tree near North Platte, NE. The inside of the tree was heavily decayed, and the larvae were feeding on decomposing matter inside of what appeared to be an old tunnel of carpenterworm.

While large, the beetles are harmless (aside from the pinch you may receive. The adults are one of our most striking beetles. In this case the larvae were not a threat to the tree, as the damage had already been done by other borers and environmental stress factors.
Left: The larvae are over 2 inches long and believed to be in the family Lucanidae.
Right: Adult male reddish brown stag beetle (Lucanus capreolus)
Compiled by David Olson, Forest Health Specialist
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