Heterobasidion annosum (Fr.) Bref. s. lato causes severe damage to forests. This study describes a model for simulating the infection and spread of Heterobasidion spp. in stands of Picea abies (L.) Karst. and Pinus sylvestris L. The model includes submodels for stand dynamics (plot simulation, growth and yield, and cross-cutting of trees) and disease dynamics: (i) spore infection, (ii) stump colonization, (iii) colonization of stump roots, (iv) vegetative transfer to tree roots, (v) spread of disease in tree roots, (vi) spread of decay in stems, and (vii) disease effect on tree growth and survival. To illustrate the model, a simulation was carried out on a Swedish Norway spruce stand where logging occurred during the high-risk season for spore infection. The model provides a means of incorporating the impact of root disease into forest planning. A change of parameters indicated that model predictions were sensitive to the spread rate and presence of initial disease centers. Further research is called for in areas related to the development of coarse root systems of various tree species and the probability and rate of transfer of disease from various sources of inoculum to healthy trees. Résumé :Heterobasidion annosum (Fr.) Bref. s. lato cause des dommages sévères en forêts. Cette étude décrit un modèle pour simuler l'infection et la propagation de Heterobasidion spp. dans les peuplements de Picea abies (L.) Karst. et de Pinus sylvestris L. Le modèle inclut des sous-modèles de la dynamique du peuplement (simulation de parcelles, croissance et rendement et coupe radiale des arbres) et de la dynamique de la maladie : (i) infection par les spores, (ii) colonisation des souches, (iii) colonisation des racines associées à la souche, (iv) transfert végétatif dans les racines des arbres sains, (v) propagation de la maladie dans les racines des arbres sains, (vi) progression de la carie dans la tige et (vii) effet de la maladie sur la survie et la croissance des arbres. Pour illustrer le modèle, nous avons fait une simulation pour un peuplement d'épicéa commun en Suède qui a été coupé pendant la saison où le risque d'infection par les spores est élevé. Le modèle permet d'incorporer l'impact de la maladie de racine dans la planification forestière. Une modification des paramètres indique que les prédictions du modèle sont sensibles au taux de propagation et à la présence, initialement, de centres d'infection. D'autres recherches sont nécessaires dans les domaines reliés au dé-veloppement du système racinaire grossier de différentes espèces d'arbres et à la probabilité et aux taux de propagation de la maladie à partir de différentes sources d'inoculum vers des arbres sains.[Traduit par la Rédaction] Pukkala et al. 84

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The root and butt rots caused by the Heterobasidion annosum species complex, hereafter referred as H. annosum sensu lato, are among the most destructive diseases of conifers. In this chapter, the host range, distribution, detection, infection biology, patterns and rate of spread, as well as the potential dispersal range of spores and temporal patterns of primary infection, of the pathogen are discussed. The factors affecting disease incidence in a stand, the estimation and prediction of disease incidence using models, and the different management strategies and tactics are described.

Airborne Heterobasidion annosum (Fr.) Bref. sensu lato infections can be controlled by winter thinning or by mechanically spreading urea or Phlebiopsis gigantea (Fr.) Jülich spores on stump surfaces during summer thinning operations. The long-term outcomes of these control methods when applied as part of the conventional forest operations are unclear. We studied the rot incidence and population structure of H. annosum in plots of Picea abies (L.) Karst. thinned in winter or thinned in summer with and without treatment of the stumps. Plots were distributed among 11 stands in Sweden representing two different land use histories: forest and agricultural. After 13 years, the effect of stump treatment on rot incidence was only evident in stands on former agricultural land. In stands planted on former forest land with higher levels of preexisting rot than on former agricultural land, the expansion of preexisting genets of H. annosum might have masked the effects of stump protection. In former forest land, unprotected summer plots showed a greater diversity of H. annosum genotypes and a smaller number of trees infected by each genet than in protected plots, suggesting that protection treatments prevented the establishment of new genets, which may result in a reduced rot incidence in the future.