268 DISEASES OF TREES 



DEFOLIATION OF TREES BY INSECTS 1 



The effects on dicotyledonous trees of defoliation by insects 

 depend on the season when it occurs. When the young shoots 

 as well as the leaves are destroyed in spring, fresh shoots are soon 

 produced by the dormant eyes of the older branches, or by the 

 buds that may have escaped at the base of the young shoots. 

 Should defoliation occur in June or July, the trees reclothe 

 themselves during August with leaves which spring from the 

 buds of the defoliated shoot itself. When defoliation takes 

 place still later, fresh leaves are either not produced at all or 

 only very sparingly. In the following year it usually happens 

 that the effects of the defoliation are entirely obliterated. The 

 wood-ring formed during the year of defoliation is narrow, and 

 the growth of the succeeding year is usually also below the 

 normal. The effects on the larch are similar to those met with 

 in dicotyledons. In mixed woods of beeches and conifers, 

 the former often suffer very severely from bark-scorching after 

 the conifers have been stripped of their leaves. 



As compared with dicotyledons, evergreen conifers usually 

 suffer very severely from defoliation, but in their case also much 

 depends on the season of the year when the damage is done. 

 Should this occur in spring, before the new shoots have been 

 formed, or in autumn, after the wood-ring has been nearly 

 or entirely completed, the life of the tree is not endangered. 

 The new shoots, being prevented from deriving any nourishment 

 from the leaves of the older branches, do not indeed develop so 

 vigorously as those of trees that have not been defoliated, still a 

 sufficient quantity of foliage is produced to enable such a tree to 

 regain its normal condition in a few years. Fatal results, on the 

 other hand, attend total defoliation at, or shortly after, the time 

 when the new shoots are formed that is to say, in May and 

 June. On account of their tender condition, the young shoots 

 are either totally destroyed or a portion persists long enough for 

 the buds to develop. In any case there is a reserve supply of 

 dormant buds, which the defoliation may stimulate to further 



1 R. Hartig, Das Erkranken und Absterben der Fichte nach der Entnade- 

 lung durch die Nonne. Forst. naturiuiss. Zeitschrift. Nos. I, 2, 3, 7, 10. 

 1802. 



