ROLE OF ARMILLARIA-CALVESCENS AND GLYCOBIUS-SPECIOSUS IN A SUGAR MAPLE DECLINE

Sugar maple, Acer saccharum Marsh., decline may be reversible during early stages before secondary insects and fungi invade stressed trees. Treatment with boric acid reduced the regenerative capacity of Armillaria calvescens Berube & Dessureault rhizomorphs and the percent infection of trembling aspen, Populus tremuloides Michx., stakes used as a bioassay. One year after treatment, crown condition and cambial electrical resistance of trees initially in early stages of crown dieback improved compared with controls. The crown condition of sugar maples previously attacked by the sugar maple borer, Glycobius speciosus (Say), did not improve during 5 years of observation, whereas 18% of uninfested trees in similar initial crown condition did improve. Sugar maple borer was more abundant in declining trees (xBAR = 5.6 galleries/tree) than is typical of nondeclining infested trees (xBAR = 1.3). Declining trees had more sugar maple borer damage than apparently healthy trees (no evidence of crown dieback). The borer and the fungus are important contributing agents that prevent recovery of many declining sugar maples.