摘要：The appearance of mass multiplication of a primary defoliator - Stereonychus fraxini L.- in the past years, which caused injuries of economic importance, imposed measures of knowledge of pest biology in order to supervise and even combat it (Simionescu et al., 2012). The research aimed at understanding the influence of defoliation caused by the Stereonychus fraxini L. beetles on the growth and vitality of forest stands with ash trees in their composition or ash forest stands. The network with permanent control surfaces was materialized in the field, there where observations and measurements were taken and biological material for laboratory analyses was periodically harvested throughout the entire vegetation season, at different stages of insect development. Defoliation causes a sensible reduction in growth of trees in forest stands. Complete, unrepeatable defoliation has important consequences on tree vitality, especially in the case of early defoliation, causing a 50-70% reduction in the vegetative mass compared to the witness trees unaffected by defoliation; the effect of defoliation manifests differently, depending on the age of the stands, being more pronounced in young stands than in older ones; repeated defoliation within the same year causes partial or total drying of the trees towards the end of the vegetation season (Blaga, 2010). The defoliation caused by Stereonychus fraxini L. in ash stands or broad-leaved stands with ash trees in their composition generates the reduction in growth of wood mass (when the defoliation exceeds 25% of the foliage surface); the age of the stands influences the reduction in growth due to defoliation, in the sense that young stands are more sensitive than old (mature) stands; in severely and very severely defoliated stands, a small percentage of dry trees is observed. Drying occurs especially among the trees belonging to the last classes in Kraft’s classification and in the case of young stands not subjected to specialized treatments/care; it would be equivalent to an accentuation of the self-elimination phenomenon (Blaga, 2010). Prevention of defoliation is possible through pest control methods. Pest control treatments manage to prevent defoliation and to put an end to mass multiplication of insects.
