Forest Insect and Disease Newsletter
2010 in the Rear-view Mirror
Division of Forestry Produces Guidelines for Managing Sites with Ash to Address the Threat of Emerald Ash Borer on Forestry-administered Lands
EAB was discovered in the United States in 2002 was found in Minnesota in 2009; currently EAB's only known occurrence within Minnesota is in the counties of Hennepin, Houston, and Ramsey. EAB populations can spread rapidly in infested firewood, logs, and ash nursery stock. Therefore, it is assumed that EAB will soon infest Minnesota's forested areas and cause significant impact to the ash resource. Ash in Minnesota comprises some 900 million trees and is the second most common hardwood tree genus in the state. Experience from other states has shown that EAB kills over 99 percent of the ash in a stand once that stand becomes infested. This level of impact is greater than what occurred with American elm following the introduction of Dutch elm disease to Minnesota.
To date, there has been no evidence of resistance to EAB within any North American ash species. Resistance does exist in some Asian ash. Subtle differences in susceptibility to EAB between white, green, and black ash have been reported, but those differences are minor and should not influence management options. All three ash species in Minnesota will likely succumb to EAB attack.
Scope of the guidance document
This document applies to:
- Forested stands classified as ash cover type
- Forested stands with an ash component of at least 20 percent of stand basal area but not typed as an ash cover type. Native plant communities where ash is and can be significant include: FDw44, MHs49, MHw36, MHc47, MHn46, FFs58, FFs59, FFn57, FFn67, WFs57, WFw54, WFn53, WFn55, WFn64.
- Forested stands with ash that are free of EAB occurrence and are greater than 25 miles from the closest known EAB infestation. This distance will allow multiple entries into a stand based on an average, "natural" movement of EAB of ~1/2 mile per year.
Ash management objectives
- Landscape perspective: Manage ash populations in the landscape to protect sensitive wetland ecotypes, reduce outbreak costs, and restrict emerald ash borer introduction and spread without eliminating ash within forest ecosystems.
- Stand perspective: Create conditions that will reduce potential impacts and increase the resiliency of forested stands by
- Keeping forested sites forested
- Maintaining an ash component but reducing the size and number of ash in the stand.
- Increasing tree species diversity.
- Management objectives should focus on ecosystem health and management, not on the emerald ash borer. The intent is to limit habitat attractiveness to EAB.
- The Division of Forestry will work within its nursery program and with other partners for maintaining representative samples of genotypes but not for processing seeds for reforestation.
- There is a likelihood that the vast majority of ash trees in Minnesota will be killed by EAB regardless of the type or magnitude of actions taken.
- The large extent of the ash resource, particularly black ash, will likely mean that sufficient management actions will not occur in all stands prior to EAB becoming established in Minnesota. Forested sites will be altered or lost.
- Little is known through research and experience how to maintain black ash forested sites as forested communities once the black ash is killed or removed. On-going research and knowledge gained through experience that can be passed along to all managers are critical to meeting long term ash management objectives. Therefore, this document presents interim guidance that will change as knowledge from research and experience is gained.
The first bona fide case of bur oak blight in Minnesota has been confirmed by Dr. Tom Harrington of Iowa State University. Symptoms of Tubakia leafspot were reported previously in portions of southern Minnesota, thought to be caused by the fungus Tubakia dryina. However, Dr. Harrington has completed testing that confirms this disease is caused by a new, as yet unnamed species of Tubakia, and he has dubbed the disease bur oak blight (BOB).
It is not clear if the new species of Tubakia is a recent arrival to this region or if a shift in climate (e.g., more early-season rain events) have made this disease more noticeable over the last two decades. To date, BOB is known to occur from eastern Nebraska to central Minnesota and southwestern Wisconsin, and it appears to be spread across all of Iowa.
Plant pathologists and arborists have been on the lookout for the new Tubakia species in Minnesota, particularly in central and more northern counties. Jill Pokorny, plant pathologist with the US Forest Service, located symptomatic bur oak trees in Mille Lacs and Sherburne counties, collected leaf samples, and identified the fungus Tubakia to be present. To determine if it was the new species that causes BOB, she submitted samples to Dr. Harrington for further laboratory testing. The samples tested positive for BOB.
In recent weeks, symptoms of BOB have also been reported on bur oaks located in Hennepin and Ramsey counties. These samples have also been submitted for species-level DNA testing, and we are awaiting test results. Jill Pokorny predicts, "As we continue to investigate symptomatic bur oak trees and more samples are tested, it is expected that BOB will be found in additional Minnesota counties."
More information on BOB
Latent Diplodia infections in red pine seedlings from Badoura and General Andrews State Nurseries in 2010
In an effort to monitor the amount of latent Diplodia infections that occur in red pine seedlings produced by the state nurseries, surveys were completed at Badoura and General Andrews Nurseries. The 2-0 and 3-0 seedlings were sampled in a systematic design and assayed for the presence of Diplodia spp. by Dr. Glen Stanosz's lab at the University of Wisconsin.
From Badoura Nursery, 260 seedlings were collected on September 20, 2010
From General Andrews Nursery, seedlings were collected on September 22, 2010.
In 2010, 19,126 acres of tamarack mortality were mapped during the aerial survey, in addition to nearly the same number of acres mapped in 2009. Most of the mortality mapped this year was in northwestern Minnesota in Lake of the Woods, Roseau and Beltrami Counties. Scattered mortality was also found throughout the range of tamarack in the state (see chart and map).
Larch beetle adults, larvae, and pupae overwinter in attacked trees. Adults emerge in the spring, seek out and bore into suitable live trees or fresh logging slash. There they construct galleries and lay eggs. Larvae hatch, feed on the phloem, eventually pupate, and become adults about 4 mm long. There is only one generation per year, but female larch beetles may produce up to 3 broods each year.
An outbreak of larch beetle has been occurring in Minnesota since 2000. During this same time period we have also experienced an unusual outbreak of larch casebearer. It has been suggested that in some areas, larch casebearer defoliation has been stressing the tamarack, leading to attack and mortality from eastern larch beetle. However, this does not appear to be the case in Minnesota, as less than 5 percent of the acres of tamarack mortality due to larch beetle have also been defoliated by larch casebearer.
To monitor populations of EAB, Minnesota Department of Agriculture (MDA) staff placed 2,840 purple prism traps statewide in 2010, with placement in three categories: risk-based, grid-based and quarantine trapping. Risk-based traps were placed at campgrounds, compost or environmental waste sites and at various other locations considered high-risk. Grid-based traps were placed in order to monitor the front line of EAB movement in seven counties along the St. Croix and Mississippi Rivers. Traps were placed based on 1.5 square-mile grids covering Anoka, Washington, Dakota, Goodhue, Wabasha, Winona, and Houston counties.
Quarantine trapping in Hennepin and Ramsey counties focused on detecting EAB movement in the known infested areas of St. Anthony Park in St. Paul and Prospect Park in Minneapolis. Using EAB population densities and ash tree inventories provided by the cities of Minneapolis and St. Paul, traps were hung in an attempt to measure how far these infestations have grown so that mitigation strategies can be employed. Traps were also placed in suburbs and in other outlying communities of Hennepin and Ramsey Counties.
Fourteen EAB adults were found on traps throughout the survey season, all from the known infested areas. Four adult beetles were collected from traps placed by MDA: two in Houston County and two in the St. Paul-Minneapolis infested area. Ten beetles were collected from traps placed by U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) staff in the St. Paul-Minneapolis infested area.
In addition, 135 trees found positive for EAB were removed in the St. Paul-Minneapolis infested area.
In September, MDA and partners including APHIS, the U.S. Fish and Wildlife Service, the U.S. Army Corps of Engineers, and the Minnesota DNR conducted the state's first release of parasitic wasps as a biological control effort to slow the spread of EAB. The release took place in the infested area of Houston County. The two species of larval parasites were approved for release and reared by APHIS in Brighton, Michigan. Tetrastichus planipennisi adults find and insert their eggs into EAB larvae. Spathius agrili lays its eggs on the outside of EAB larvae. The developing wasps feed on and eventually kill the EAB larvae. MDA released the wasps after extensive testing confirmed they will not harm people, other animals or the environment.
March, 2011 marked the fourth year of Forest Pest First Detector workshops taught by the award-winning Minnesota Forest Pest First Detector training team, comprised of representatives from University of Minnesota Extension (UMnExt), the Minnesota Department of Agriculture (MDA), and the Minnesota Department of Natural Resources (DNR). Minnesota is the first state to use the NPDN to focus on detecting forest pests. Using a step-by-step process to identify signs and symptoms of invasive forest pests, the first year of workshops focused on identifying infestations of emerald ash borer (EAB). While continuing to emphasize EAB, training in subsequent years expanded its focus to other forest pests such as gypsy moth, bur oak blight, Asian long-horned beetle, thousand cankers disease, and mountain pine beetle.
Before attending a First Detectors workshop, participants are required to complete three online modules: NPDN Overview and Missions, Minnesota Invasive Species Program, and How to Collect and Package Weed, Insect, and Plant Samples. Before walking in the door, First Detector candidates arrive armed with background knowledge, bringing their printed module completion forms to prove it.
UMnExt houses the database of Minnesota's First Detectors and directs calls from concerned citizens who think they've spotted a pest to a trained Minnesota First Detector. The First Detector can then determine if the call warrants a site visit. In addition, Minnesota First Detectors can contact the MDA themselves using the MDA's Arrest-the-Pest hotline at the first sign or symptom of EAB or other forest pests.
In the past three years, UMnExt referred 463 out of 1,229 calls regarding potential forest pests to First Detectors. In 2010, First Detectors volunteered 1,316 hours and traveled 7,733 miles, which resulted in a total public value of nearly $29,000. The discovery of EAB by a tree care worker in St. Paul on May 13, 2009 was a result of First Detector training, demonstrating the value of the Forest Pest First Detector program.
These popular workshops attracted 180 participants in 2008, 146 in 2009, 152 in 2010, and 203 in 2011. In all, 411 volunteers from 66 out of 87 Minnesota counties have committed to becoming First Detectors. Volunteers from Wisconsin, Iowa, North Dakota, and South Dakota have also attended the workshops. Passion for healthy forests and trees must run deep in these volunteers: several First Detectors have attended additional trainings for updated information! Minnesota"s army of detectors is on alert.
Spruce budworm is a native insect in North America. Massive outbreaks periodically occur in spruce-fir forests of eastern Canada and the United States. Since 1954, when annual aerial sketch-mapping began, spruce budworm has caused defoliation of balsam fir and white spruce every year in Minnesota. This year, we observed 121,492 acres of defoliation in northeastern counties (see map below). This is slightly more than double last year's defoliation. Defoliation was greater than 50 percent on 114,800 of the acres. The major area of defoliation has shifted to the east and south and now extends from the western edge of Lake Vermillion to east of Ely into Lake County on the north and from Buhl to Hoyt Lakes on the south. Almost 5,000 acres were defoliated near Pequaywan Lake in the Cloquet Valley State Forest in southeastern St Louis County, and another 1,200 acres near the Knife River in extreme in southeastern St Louis County. Mortality and top-kill begin to occur after 3 to 4 years of heavy defoliation in balsam fir. Defoliation on the western end of Lake Vermillion has been occurring since at least 2003.