Thousand cankers disease, caused by the walnut twig beetle (Pityophthorus juglandis Blackman) and an associated fungal pathogen (Geosmithia morbida M. Kolarík, E. Freeland, C. Utley, and N. Tisserat), threatens the health and commercial use of eastern black walnut (Juglans nigra L.), one of the most economically valuable tree species in the United States. Effective phytosanitary measures are needed to reduce the possibility of spreading this insect and pathogen through wood movement. This study evaluated the efficacy of heat treatments and debarking to eliminate P. juglandis and C. morbida in J. nigra logs 4-18 cm in diameter and 30 cm in length. Infested logs were steam heated until various outer sapwood temperatures (60, 65, and 70 degrees C in 2011; 36, 42, 48, 52, and 56 degrees C in 2012) were maintained or exceeded for 30-40 min. In 2011, all heat treatments eliminated G. morbida from the bark, but logs were insufficiently colonized by P. juglandis to draw conclusions about treatment effects on the beetle. Debarking did not ensure elimination of the pathogen from the sapwood surface. In 2012, there was a negative effect of increasing temperature on P. juglandis emergence and G. morbida recovery. G. morbida did not survive in logs exposed to treatments in which minimum temperatures were 48 degrees C or higher, and mean P. juglandis emergence decreased steadily to zero as treatment minimum temperature increased from 36 to 52 degrees C. A minimum outer sapwood temperature of 56 degrees C maintained for 40 min is effective for eliminating the thousand cankers disease vector and pathogen from walnut logs, and the current heat treatment schedule for the emerald ash borer (60 degrees C core temperature for 60 min) is more than adequate for treating P. juglandis and G. morbida in walnut firewood.

Select insecticides can significantly reduce transmission of CYSDV. However, insecticide management of CYSDV incidence in cantaloupes has limitations in chronically high infestation areas such as the southwestern USA, and is often only able to delay disease onset rather than prevent its occurrence. © 2016 Society of Chemical Industry.

In the past decade, black walnut (Juglans nigra) trees throughout western North America have suffered from widespread branch dieback and canopy loss, causing substantial tree mortality (2,3). The fungus, Geosmithia morbida, vectored by the walnut twig beetle (WTB), Pityophthorus juglandis, has been associated with this devastating disease known as Thousand Cankers Disease (TCD) (2,3). In August of 2012, branch samples from TCD symptomatic black walnut trees (5 to 10 cm in diameter and 15 to 30 cm long) were collected on the North Carolina side of the Great Smoky Mountain National Park (GRSM) in Cataloochee Cove (35°37.023′ N, 83°07.351′ W) and near the Big Creek Campground (35°45.290′ N, 83°06.473′ W), in Haywood County. Five symptomatic trees near the Big Creek Campground and three from Cataloochee Cove displayed typical TCD signs including progressive crown thinning, branch flagging, and branch dieback; however, insect holes were not observed. Samples were double bagged in Ziploc plastic bags, sealed in a 19-liter plastic bucket, and transported to the University of Tennessee. Outer bark was removed from the samples and small, elliptical, necrotic cankers were observed. Wood chips (3 to 4 mm2) from cankers were excised and placed on 1/10 strength potato dextrose agar amended with 30 mg/liter streptomycin sulfate and 30 mg/liter chlortetracycline HCL and incubated on a 12-h dark/light cycle at 22°C for 5 to 7 days. Fungal isolates were tentatively identified as G. morbida by using culture morphology, and characteristics of conidiophores and conidia (2). The isolated fungus from the Cataloochee Cove location was grown in 1/10 strength potato dextrose broth at room temperature for 2 weeks. Isolates from Big Creek Campground were contaminated and were not analyzed further. Fungal colonies were tan to light yellow. Conidia were tan, subcylindrical, and catenulate. Conidiophores were multibranched, verticillate, and verrucose. To verify the morphological data, DNA was extracted from fungal mycelia using DNeasy Plant Mini Kit (Qiagen, Valencia, CA) according to the manufacturer's published protocol. Isolates from Cataloochee Cove were characterized using ITS1 and ITS4 universal primers (4). The putative G. morbida isolate (GenBank Accession No. KC461929) had ITS sequences that were 100% identical to the G. morbida type isolate CBS124663 (FN434082.1) (2). Additionally, fungal DNA from Cataloochee Cove was amplified using G. morbida-specific microsatellite loci (GS04, GS27, and GS36) (1). PCR products were analyzed with the QIAxcel Capillary Electrophoresis System (Qiagen) and were similar to those previously published (2). To date, all confirmed cases of TCD in the native range of black walnut have been in urban areas, along rural roadsides and/or fence rows. The report in North Carolina is the first finding of G. morbida, the causal agent of TCD, in a forest setting. References: (1) D. Hadziabdic et al. Conserv. Genet. Resources 4:287, 2012. (2) M. Kolarik et al. Mycologia 103:325, 2011. (3) N. Tisserat et al. Plant Health Progr. doi:10.1094/PHP-2011-0630-01-BR, 2011. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, CA, 1990.

Thousand cankers disease (TCD) is an insect-mediated disease of walnut trees (Juglans spp.) involving walnut twig beetle (Pityophthorus juglandis) and a fungal pathogen (Geosmithia morbida). Although first documented on walnut species in the western U.S., TCD is now found on black walnut (J. nigra) in five states in the eastern U.S. Most collections of P. juglandis or G. morbida are from trees in agriculturally- or residentially-developed landscapes. In 2013, 16 pheromone-baited funnel traps were deployed in or near black walnuts in forested conditions to assess the risk of infestation of forested trees by P. juglandis. Four of the 16 funnel traps collected adult P. juglandis from three forested areas (one in North Carolina and two in Tennessee). These collections, while in forested settings, may still be strongly influenced by human activities. The greatest number of P. juglandis (n = 338) was collected from a forested location in an urbanized area near a known TCD-positive tree. The other two forested locations where P. juglandis (n = 3) was collected were in areas where camping is common, and infested firewood may have introduced P. juglandis unintentionally into the area. Future studies to assess P. juglandis on more isolated forested walnuts are planned.

Black walnut, a valuable economic and environmentally important species, is threatened by thousand cankers disease. Systemic imidacloprid and dinotefuran applications were made to mature black walnut trees to evaluate their translocation and concentration levels in various tissue types including leaf, twig, trunk core, nutmeat, and walnut husk. The metabolism of imidacloprid in plants produces a metabolite, olefin-imidacloprid, which has been documented to have insecticidal properties in other systems. Trunk CoreTect (imidacloprid) soil pellets and a trunk spray of dinotefuran were applied to mature black walnuts in spring 2011. Imidacloprid concentrations were detected in both the lower and upper strata in all tissue types tested and progressively increased through month 12 post-treatment in twig and leaf tissue. Olefin-imidacloprid was detected in the nutmeat and walnut husk. Dinotefuran was only detected in the first sampling period and was found in low concentration levels in leaf and twig tissue types, and was not detected in the trunk, nutmeat or the walnut husk.