| Currently eastern hemlock Tsuga canadensis L. existence in the hemlock-hardwood forest is severely threatened by the hemlock woolly adelgid, Adelges tsugae Annand. This is an important economic pest and has already destroyed large tracts of eastern hemlocks in Virginia, Maryland and southern Connecticut. Chemical controls are not possible nor desirable over large forests. Alternate methods to manage the problem including biocontrol are being tried, with some reported success. Several factors contribute to the death of hemlocks. These include the removal of nutrients during HWA feeding, thereby lowering resistance, and the subsequent invasion by other pests such as scale, mites and blight. Drought stress in addition can hasten death. The exact mechanisms by which tree death occurs are still unknown. The role of duration and severity of infestations and saliva toxicity are still to be studied. This study documents the changes that occur in host plant morphology, anatomy, and physiology as a result of adelgid feeding, and the role of organic biostimulants (Roots™) in ameliorating the effects of insect damage.; HWA infestation reduces seedling height, diameter, needle area, needle dry weight and total biomass production. In contrast, specific leaf area and photosynthetic rate per unit leaf area are higher in infested seedlings indicating compensation for infestation. However, per plant photosynthesis is lowest in infested seedlings.; Adelgid densities were significantly reduced on hemlock seedlings treated with organic biostimulants, which are essentially a stress vitamin mix. Height and diameter growth, above-ground bio-mass, cell wall thickness, xylem cell numbers, lumen and tracheid diameters, needle and cuticle thickness in infested seedlings treated with organic biostimulants were significantly higher than infested controls not treated with the biostimulants.; Results of this study allow speculation that site conditions determine whether infested trees will survive. Trees on water stressed sites are more likely to die due to HWA infestation, than trees growing on moist sites. Under experimental conditions the regular supply of water and nutrients was found to reduce the impact of adelgid feeding on seedling health and vigor. |
