Occurrence of disease symptoms and selected biotic factors connected with beech (Fagus sylvatica L.) dieback phenomenon in stands of The Magurski National Park

The studies were carried out in 12 beech stands, growing on mountain fresh forest site in Magurski National Park. Stands differed in respect of exposition (northern and southern) and age - lower age classes (21-60 years old) and higher age classes (81-120 years old). This paper presents evaluation of frequency of disease symptoms occurrence in the crowns and on the trunks of beeches. The presence and the place of occurrence of fungus <i>Ascodichaena rugosa</i> and insects <i>Cryptococcus fagisuga</i> and <i>Ectoedemia liebwerdella</i>, which could be connected with beech bark necrosis on the trunks were noted down. In each stand 50 trees, growing side by side in center of the stand, were analyzed. Among 600 analyzed trees of <i>Fagus sylvatica</i>, 2.6% had a dead top. Crown thinning were present on 51.8% of trees. It appeared frequently in higher age class stands and didn't cover more than ¼ of the crown. Moreover, in crowns of 4.1% of trees the leaf chlorosis appeared. The most frequent symptom on trunks of beeches were local necroses (98% of trees), that were sometimes connected with slime fluxing (3.3%). Necroses were the most number in stands growing on the southern exposition and on south parts of the trunks. <i>Cryptococcus fagisuga</i> appeared mostly in high age class stands. Intensity of its appearance was similar on the trees growing on the southern and northern exposition (respectively, 48.3% and 53.3%). Particular parts of the trunks were colonized with similar frequency by <i>C. fagisuga</i> irrespective of cardinal points (N-29.3%; S-21.7%; W-22.7%; E-26.2%) and number of necroses on the trunks. <i>Ascodichaena rugosa</i> appeared on 8.6% of trees, more frequently on their north parts of the trunks (7.3%). In the places colonized by fungi <i>A. rugosa</i>, insect <i>C. fagisuga</i> was absent. Occurrence of larvae of <i>Ectoedemia liebwerdella</i> was mostly found on trunks of beeches growing on the southern exposition (43.0%), on 35.3% of trees they colonized south parts of trunks. There wasn't observed any connection between the occurrence of these larvae and symptoms of local necroses.

Distribution of American Beech (Fagus grandifolia) and Beech Scale (Cryptococcus fagisuga Lind.) in Michigan from 2005 to 2009

Beech scale (Cryptococcus fagisuga Lind.) (Hemiptera; Coccidae), an invasive insect associated with beech bark disease, was discovered in 2000 in a localized area of northwest Lower Michigan and one area in the eastern Upper Peninsula. From 2005 to 2009, we surveyed 809 sites in 73 Michigan counties to determine whether American beech (Fagus grandifolia) trees were present and, if so, whether trees had been colonized by beech scale. Beech trees were present in 696 sites in forest, recreation, and residential areas. By 2009, beech scale had infested beech trees in 8 of 15 counties in the Upper Peninsula, 14 of 68 counties in the Lower Peninsula, one of three islands in Lake Michigan, and all three sampled islands in Lake Huron. Colonization of islands more than 20 km from infestations on the mainland suggest that beech scale was likely introduced by humans or birds. Rates of expansion of 12 discrete beech scale populations varied from 3.3 to 14.3 km per year.

Evaluation of Resistance to the Beech Scale Insect (Cryptococcus fagisuga) and Propagation of American Beech (Fagus grandifolia) by Grafting

Scions collected from diseased trees and from those without symptoms of beech bark disease (BBD) were cleft-grafted in 2003 and 2004 onto rootstock of unknown resistance to BBD. Grafting success varied among genotypes and year (30% in 2003 and 12% in 2004), and improved with increasing rootstock diameter. Successful grafts were used to test resistance to the beech scale insect, Cryptococcus fagisuga (the initiating agent of BBD) by introducing eggs onto the bark of scions and allowing time for the emergence of all developmental stages of the insects. Significantly fewer insects colonized scions collected from putatively resistant trees than those collected from diseased trees. In some cases, where egg placement overlapped a portion of the rootstock, insect colonies developed on the rootstock but not on the scion collected from resistant trees. Occasionally, scions from putatively resistant trees were colonized, whereas some of those from diseased trees were not. When scions from putatively resistant trees were heavily colonized, only adult insects were present and no eggs or other life stages of the insect were found. The findings indicate that the extent of resistance to the scale insect (hence to BBD) ranges from partial to total resistance.