A Four-Year, Seven-State Reforestation Trial with Eastern Hemlocks (Tsuga canadensis) Resistant to Hemlock Woolly Adelgid (Adelges tsugae)

We conducted over a decade of research into individual eastern hemlock (Tsuga canadensis; hemlock) trees that are potentially resistant to hemlock woolly adelgid (Adelges tsugae; HWA), an invasive xylem-feeding insect that is capable of rapidly killing even mature trees. Following clonal propagation of these individuals, in 2015 we planted size- and age-matched HWA-resistant and HWA-susceptible hemlocks in HWA-infested forest plots in seven states. In 2019, we re-surveyed the plots; 96% of HWA-resistant hemlocks survived compared to 48% of susceptible trees. The surviving HWA-resistant trees were also taller, produced more lateral growth, retained more foliage, and supported lower densities of the elongate hemlock scale Fiorinia externa, another invasive hemlock pest, than the surviving HWA-susceptible trees. Our results suggest that HWA management may benefit from additional research exploring the identification, characterization, and use of HWA-resistant eastern hemlocks in future reforestation efforts.

Elongate hemlock scale, an exotic scale insect pest of Christmas trees and other conifers

Elongate hemlock scale, Fiorinia externa Ferris (Hemiptera: Diaspididae), is an armored scale insect native to Japan and eastern Asia. This insect was first documented in the United States in 1908 in Queens, NY, and has since spread throughout most of the eastern United States. Though the primary hosts of the pest, hemlocks and firs, do not occur in Florida, there are concerns that elongate hemlock scale coming into the region on cut Christmas trees may disperse and establish on conifers that do occur in Florida. Of specific interest are two endangered species, Florida torreya (Torreya taxiflora) and Florida yew (Taxus floridana), which are native to a small region in northwestern Florida. Also of concern are Florida forestry species, Florida Christmas tree species, and species used for ornamental plantings in Florida. What can Florida do to protect its native conifers and farmed trees from the elongate hemlock scale? Find out in this 5-page fact sheet written by Adam Dale, Travis Birdsell, and Jill Sidebottom and published by the UF/IFAS Entomology and Nematology Department. http://edis.ifas.ufl.edu/in1253

Susceptibility of Chinese Hemlock (Tsuga chinensis) to Injury from Autumn Horticultural Oil Applications

Chinese hemlock (Tsuga chinensis) has been suggested as a possible replacement in landscape plantings for eastern hemlocks (T. canadensis), which are being lost due to infestations of hemlock woolly adelgid (Adelges tsugae). Chinese hemlock is highly resistant to hemlock woolly adelgid, but is a host for elongate hemlock scale (Fiorinia externa). Horticultural oil is a popular insecticide commonly used by professionals to manage various insect and mite pests of hemlock in landscapes, including hemlock woolly adelgid, spruce spider mite, and armored scales. In tests, horticultural oil applied in two separate autumn sprays was not phytotoxic to Chinese hemlocks. Therefore, 1% or 2% horticultural oil may be used to maintain Chinese hemlocks in landscape plantings.

Eastern hemlock (Tsuga canadensis) regeneration in the presence of hemlock woolly adelgid (Adelges tsugae) and elongate hemlock scale (Fiorinia externa)

The hemlock woolly adelgid (Adelges tsugae Annand) is an invasive hemipteran that poses a major threat to eastern hemlock (Tsuga canadensis (L.) Carrière) forests in the United States. We conducted three surveys over a five-year period that assessed the density of hemlock woolly adelgid (HWA) and a second invasive pest, the elongate hemlock scale (EHS; Fiorinia externa Ferris), overstory hemlock mortality, and hemlock regeneration in ~140 hemlock stands (mean size, 44 ha; range, 7–305 ha) within a 7500 km2 north–south transect of southern New England (USA). In each stand, we rated HWA and EHS density on 50 hemlock trees using a 0–3 scale (0, none; 1, 1–10 organisms/m branch; 2, 11–100 organisms/m branch; 3, >100 organisms/m branch). Data on the presence or absence of regeneration were taken in 2005; in 2007 and 2009, we quantitatively assessed regeneration by counting the number of hemlock seedlings in three 16 m2 plots per stand. In 2005, 81% of sampled stands had HWA, 72% had EHS, and 66% had hemlock regeneration. In 2007, 86% of sampled stands had HWA, 79% had EHS, and 46% had hemlock regeneration. In 2009, 91% of stands had HWA, 87% had EHS, and 37% had hemlock regeneration. The proportion of stands with hemlock regeneration declined 46% between 2005 and 2009, and hemlock seedling density declined 71% between 2007 and 2009. A best-fit model selection algorithm found that this decrease was inversely correlated with stand-level adelgid density. There was no correlation between the change in seedling density and stand-level density of the elongate hemlock scale. The apparent decline in regeneration suggests that the ecosystem-level changes currently occurring in southern New England may be difficult to reverse.

Description of the adult male elongate hemlock scale, Fiorinia externa Ferris (Coccoidea: Diaspididae), with notes on the seasonal development of the species on eastern hemlock, Tsuga canadensis (L.) Carrieré (Pinaceae), in the southern Appalachian region (U.S.A.)

The adult male of Fiorinia externa Ferris is described for the first time. Its morphology agrees with that of previously described adult males in the tribe Diaspidini, and suggests a close affinity to Pseudaulacaspis. F. externa has two complete overlapping generations per year on the needles of eastern hemlock, Tsuga canadensis (L.) Carrieré, in the eastern Tennessee (USA) southern Appalachians. Adult females (both gravid and non-gravid) and first-instar nymphs were the dominant overwintering stages, although all stages apart from the adult males were present throughout the winter months. Adult males began emerging in mid March with emergence peaks in mid April to early May and again in mid to late September.