SummaryChina has 12 taxa of white pines (subgenus Strobus), including species of wide distribution valuable to plantation forestry and species of rare endemics only distantly related to other white pines. The most important forest diseases of these white pines are caused by the blister rust fungi of the genus Cronartium that alternate to telial host species of Ribes and Pedicularis. The most serious infestations have occurred in southwestern China on Pinus armandii and in northeastern China on P. koraiensis. The blister rust pathogen on P. armandii has usually been identified as Cronartium ribicola. Several lines of evidence, however, imply this pathogen on P. armandii is different from a pathogen on P. koraiensis that appears more closely related to C. ribicola in North America, Europe, and other Asian countries. In China, C. ribicola is designated as a quarantine pest. Silvicultural control of blister rust relies on pruning and thinning infected trees, herbicide removal of telial hosts, and chemical treatment of blister rust cankers. Although plantation forestry is important in China, little information is available on the genetics of resistance in Chinese white pines to native blister rust fungi. Challenges and opportunities are identified in forest management and research for disease assessment and control, rust systematics and biology, and genetic interactions in the white pine blister rust pathosystem.

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& Key message We assessed the impact of the polyphagous shot hole borer (PSHB), Euwallacea whitfordiodendrus (Schedl), and Kuroshio shot hole borer (KSHB), E. kuroshio Gomez and Hulcr, on hardwood trees in southern California, southwestern China, and northwestern Vietnam. The highest levels of mortality were recorded from 10 of 39 tree species in the survey, and these were primarily native tree species. & Context Two invasive shot hole borers represent relatively recent introductions in southern California, USA, and continue to spread and cause injury and mortality to several native and ornamental tree species. They originate from Southeast Asia. & Aims Knowledge of tree species susceptibility to these wood-boring beetles is essential to inform better pest management and to evaluate future risk for urban and wildland forests. & Methods From 2012 to 2016, ground surveys were conducted in the invaded and native regions at PSHB/KSHB-infested and PSHB/KSHB-uninfested sites to record levels of tree injury and mortality on native and ornamental tree species. & Results In California, several native species of maple, Acer, willow, Salix, and sycamore, Platanus, were infested by either PSHB or KSHB at high rates (> 70%), and comparative rate of infestation by KSHB in all trees and in native trees surpased that by PSHB, whereas rate of infestation by PSHB in ornamental trees surpassed that by KSHB. Mortality of two maple species caused by PSHB exceeded 20%, whereas background mortality rate of hardwoods was 2% in uninfested areas. & Conclusion These data should inform land managers about the tree species at most risk to injury and mortality, facilitate detection ground surveys, and direct prophylactic treatments for these invasive woodborers. Keywords Ambrosia beetles. Hardwood tree mortality. Impact assessment. Invasive species This article is part of the topical collection on Entomological issues during forest diebacks

Diseases and insects, particularly those that are non-native and invasive, arguably pose the most destructive threat to North American forests. Currently, both exotic and native insects and diseases are producing extensive ecological damage and economic impacts. As part of an effort to identify United States tree species and forests most vulnerable to these epidemics, we compiled a list of the most serious insect and disease threats for 419 native tree species and assigned a severity rating for each of the 1378 combinations between mature tree hosts and 339 distinct insect and disease agents. We then joined this list with data from a spatially unbiased and nationally consistent forest inventory to assess the potential ecological impacts of insect and disease infestations. Specifically, potential host species mortality for each host/agent combination was used to weight species importance values on approximately 132,000 Forest Inventory and Analysis (FIA) plots across the conterminous 48 United States. When summed on each plot, these weighted importance values represent an estimate of the proportion of the plot’s existing importance value at risk of being lost. These plot estimates were then used to identify statistically significant geographic hotspots and coldspots and of potential forest impacts associated with insects and diseases in total, and for different agent types. In general, the potential impacts of insects and diseases were greater in the West, where there are both fewer agents and less diverse forests. The impact of non-native invasive agents, however, was potentially greater in the East. Indeed, the impacts of current exotic pests could be greatly magnified across much of the Eastern United States if these agents are able to reach the entirety of their hosts’ ranges. Both the list of agent/host severities and the spatially explicit results can inform species-level vulnerability assessments and broad-scale forest sustainability reporting efforts, and should provide valuable information for decision-makers who need to determine which tree species and locations to target for monitoring efforts and pro-active management activities.

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