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Emerald Ash Borer Biocontrol
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Left: Two T. planipennisi, a larval parasitoid of EAB, about 2mm long
Right: O. agrili, an egg parasitoid of EAB, 1mm in length. Photo: Jian Duan USDA-APHIS
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Help may be on the horizon for ash trees in Nebraska. This year, the USDA began releasing EAB biological control agents in 4 locations in the eastern part of the state including Mahoney State Park, Platte River State Park, Fremont Lakes State Park, and Pioneers Park in Lincoln. These small parasitic wasps have been successfully introduced in many parts of the Eastern US, and researchers are hopeful that they may help to control EAB populations in the future.
The main agents being released are an egg parasitoid wasp (Oobius agrili), and two larval parasitoids (Tetrastichus planipennisi and Spathius galinae). These wasps do not sting and are completely harmless to humans. Additionally, through extensive testing, they are only known to attack emerald ash borer. The hope is that in the future these wasps will act as a natural enemy to EAB and thus be able to help keep its populations at more manageable levels.
The parasitoids are released either as adults, or in "bolt" or "obinator" form. The bolts are sections of an ash tree that have been infested with EAB then exposed to T. planipennisi to be parasitized. Within a few days to weeks multiple new broods of the wasp will hatch out. Similarly, the obinators are containers filled with EAB eggs laid on filter paper that have been parasitized, from which newly hatched wasps will emerge and seek new hosts in the wild. These releases will be done on a weekly basis throughout the summer to increase the chance of establishment.
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Left: a bolt of ash with T. planipennisi which will emerge and seek out EAB larvae.
Right: an obinator filled with O. agrili which will parasitize EAB eggs.
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Trees infested with Zimmerman pine moth will need to be treated a second time starting around the second week of August (The first treatment should have been done the 2nd week of April). During this time, larvae will once again be active and at a stage where they will be exposed to the pesticide.
Unlike many tree pests, which cause little damage, Zimmerman pine moth can be quite damaging to young trees and thus control is warranted. Trees should be bark drenched with either permethrin or bifenthrin, taking caution to follow all pesticide safety label instructions (be aware that some pesticides may list it incorrectly as a foliar pest).
Evidence of Zimmerman pine moth includes popcorn like masses of pitch on the base of branches as well as possible branch failure from the larvae feeding underneath the bark.
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Many citizens in the eastern part of the state have noticed high levels of this pesky beetle following a late emergence this year. Japanese beetles are a highly invasive insect that are known to feed on over 350 species of plants, and Nebraska is the front line of the invasion. Some trees, such as lindens, are favorites of the adult beetle and can be completely defoliated or skeletonized.
Unfortunately, treatments are extremely limited. Lindens are poor candidates for systemic insecticides since most of these products are neonicotinoids and thus extremely toxic to bees when the tree blooms. Likewise, foliar sprays can be difficult on large trees and may need to be applied multiple times in order to fend off new arrivals of beetles. In many cases the tree is already defoliated before it can be sprayed. However, as long as the tree is healthy it should be able to recover from the attack, either by sending out new growth or simply returning next year. Japanese beetle populations should also start to fluctuate from year to year once it establishes in an area due to pressure from things such as predators, environmental conditions, and disease.
Another reminder is to avoid using Japanese beetle traps, which are available at many stores. While these traps are extremely effective and can be quite satisfying, they actually draw more beetles into an area than they are able to catch, making the problem worse.
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Left: The early stages of feeding by Japanese beetle
Right: A heavily defoliated linden,
Photo Credit: Steven Katovich, USDA Forest Service, Bugwood.org
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Sawflies are often misidentified as caterpillars but actually belong to the same order as bees and wasps. The larvae can be most easily distinguished as having six or more pairs of ‘prolegs’ (those fleshy looking legs behind the three pairs near the head).
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Left: a caterpillar with 5 sets of prolegs, Photo credit: Diane Brown, Michigan State University Extension
Right: Sawfly larva with 7 prolegs, Photo credit: Natural Resources Canada
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Often, damage from sawflies can be found on oak leaves as the larvae skeletonize the tissue, leaving behind a network of veins. In most cases this damage is minor and will go unnoticed, however in the case of this English oak, almost the whole tree was impacted. While this certainly looks bad, if the tree is in good health it should be able to recover provided it doesn’t get hit like this several years in a row and the tissue in the stems is still alive.
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At a glance these leaves look brown, but a closer inspection reveals the tissue between the veins is actually gone. The sawfly larvae which caused this are no longer present.
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Sudden Oak Death in Nebraska
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Recently, a number of great plains states discovered that rhododendron nursery stock infested with the pathogen Phytophthora ramorum, which causes sudden oak death, had been imported into various states. This disease has killed many oaks, particularly in California and Oregon. At this time, all of the infested stock has been destroyed and the pathogen has not been found outside of that in the state. The pathogen is not well suited to survive in the climate of Nebraska since it thrives in mostly wet conditions and has been a problem in areas where rainfall exceeds 50 inches per year. The red oak group is believed to be more at risk than the white oak group. Symptoms include bleeding cankers on the trunk with the leaves turning brown and the tree dying quickly. Suspected sudden oak death should be reported to the Nebraska Plant and Pest Diagnostic Clinic at 402-472-2559.
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Map showing risk for sudden oak death in the lower 48 states.
Kelley et al. 2005
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The gold dust buprestid is much larger than EAB, with characteristic gold spots on the back.
Photo Credit: Beth Arens
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A beautiful jewel beetle, this member of the Buprestidae family feeds as a larva on declining cottonwoods and other poplar species. Its overall shape and appearance make it easy to mistake for the invasive member of its family, the emerald ash borer. The gold dust buprestid generally is a larger insect with a wider overall shape than EAB. Additionally, it will often have distinct gold flecks where EAB tends to be more solid in color.
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Compiled by David Olson, Forest Health Specialist
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