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Birmensdorf, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) 227-228.
OCCURRENCE OF FOREST INSECT PESTS AND FUNGAL DISEASES IN CZECHIA IN 1998
Jan Liska, Petr Kapitola & Vitezslava Peskova Forestry and Game Management Research Institute
Jiloviste-Strnady, CZ-156 04, Praha 5- Zbraslav, Czech Republic
The data given below represent about 75% of forest area in Czechia from where numbers are available (an area of ea 2 000 000 ha). Occurrence can be quantified in insect pests but not in fungal diseases for which number data are lacking from the territory of Czechia in the present.
Insect pests
The conditions in 1998 can be generally considered as rather unfavourable for development of forest insect pests. Practically in all of the observed insect groups
considerable decrease of infested areas was recorded. Only in some cases this decrease was a result of conducted control measures.
The complex of bark-feeding insects on Norway spruce, first of all Ips typographus and other bark beetles, belongs to the most significant forest insect pests in the conditions of Czechia for decades. Their last extensive outbreak has been recorded just in the nineties (1992-1996) when a total of 6 150 000 m3 of spruce wood was infested by these pests. In last two years the amount of wood infested has markedly decreased (1997- 390 000 m3, 1998- 330 000 m\ Within the country the situation in 1998 was worst again in the Sumava Mts., in conjunction with the outbreak of Ips typographus in the National Park of Sumava (74 000 m3).
In the same period as in spruce (1993-1996), also Scots pine stands were affected by outbreak ofbark borers; during these years about 220 000 m3 of pine wood were infested.
Similarly to 1997, neither in 1998 these pests caused any significant damage (a total volume of 2 600 m3 was infested what is almost by half less than in 1997).
The situation was similar in bark-feeding pests of other coniferous trees, larch and fir, which population numbers were in general lower last year.
As far as broadleaved trees are concerned, last years smaller damage is caused regularly by the bark beetles Hylesinus crenatus and Leperisinus fraxini on ash, and by Scolytus ratzeburgi on birch. Higher attention should be paid to bark and wood borers in oak stands. An
increasing harmful occurrence was observed mainly in the bark beetle Scolytus intricatus, the siricid Xiphydria longicollis and the buprestids of the genus Agrilus.
Of defoliating insect pests which infest coniferous trees are in the last period important mainly those damaging the spruce stands. In the stands of other conifers no significant damage has occurred in the last period.
In this decade, the most important outbreak has been represented by the gradation of Lymantria monacha in years 1993-1996. As it was expected, any high population density of this pest was not found out in 1998. Of great importance are further the spruce sawflies of the genus Cephalcia; last year an outbreak only of Cephalcia arvensis s. 1. was recorded in traditional focus in east Bohemia (600 ha). In spruce tenthredinids, first of all Pristiphora abietina, the similar infested area as in 1997 was recorded (increase by ea 5% to 4 400 ha).
In another significant pest of spruce stands, Zeiraphera griseana, any reports on its harmful occurrence were not received again.
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To the most important defoliating insect pests on broadleaved trees belongs a complex of tortricids and geometrids living on oaks, with the dominant species Tortrix viridana. On the contrary to previous years, the extent of severe defoliation markedly decreased, from
approximately 16 000 ha in 1997 to 4 800 ha in 1998.
The continuing outbreak of the moth Cameraria ohridella, feeding on horse chestnut, causes in forest stands problems in game preserves where negatively influences the chestnut crop. However, the health condition ofhorse chestnuts in general is not seriously endangered for the time being.
Of other insect groups, the large pine weevil (Hylobius abietis) damaged conifer plantations covering 2 300 ha last year. The extent is still at low level in long-time measurement. In sucking insects no significant damage was reported.
Fungal diseases and physiological disorders
In 1998 precipitation was very unsteady (dry winter and spring, the wet beginning of summer and again dry autumn), and considerably influenced the occurrence of fungal diseases. It concerns particularly to forest nurseries, where relatively low incidence was recorded in soil fungi causing seedling damping-off, and also the damage of seedlings by Botrytis cinerea was less spread than in other years.
In recent years, plants (first of all ofbeech) are more frequently infested by fungi ofthe genera Verticillium, Fusarium, Cylindrocarpon and others, which cause diseases of tracheomycotic character.
Infections of the pine needle cast (Lophodermium spp.) in nurseries were in general not so high nevertheless there occurred high to total losses of pine planting stock in some localities.
Production of oak plants has been increased because of higher crop of acorns in last two years; however, the incidence of Microsphaera alphitoides intensified as well.
Of the significant rusts, first of all Coleosporium sp. div. should be mentioned. In recent years it spreads epidemically in pine plantations in some areas.
As far as the complex diseases of stands are concerned, the extent of so called ,spruce yellowing" remained at similar level as in 1997. The significant phenomenon of last years is still beech withering in mature and premature stands.
Serious damage was last year caused by wood-destroying fungi among them Armillaria spp. were dominated; it was first of all Armillaria ostoyae on conifers of all ages, also higher occurrence of Arm ill aria gallica in older broadleaved stands was recorded. Of the wide spectrum of wood-destroying fungi Stereum sanguinolentum, a significant injury parasite of conifers, should be mentioned as well.
Dying ofbroadleaved trees (first of all oaks) with tracheomycotic symptoms, widespread in Czechia mainly in the eighties, continued to decline also in 1998.
In the conclusion of the presented short contribution it can be said that the year 1998 was really favourable for forest protection as far as the occurrence of forest insects and diseases is concerned. It is our wishing for the forests in Czechia, so suffering in the past, to get also over future years with only a low impact of biotic harmful agents.
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