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Damage and pests

Plantations of poplars, aspens and willows may be attacked by a variety of fungal and bacterial pathogens, which are harmful both to leaves, shoot tips and stems, while insects mainly damage the leaves.  Frost damage is another problem that could cause dieback, especially for younger willow in combination with bacterial infections.

Defense against diseases and pests is very much a matter of managing measures, in addition to the use of resistant clones. The commercial plant clones on the market today are generally both frost tolerant and show good resistance towards diseases.

A serious problem is that the pathogens are highly adaptable and evolve as new varieties emerge after some time, which will break the resistance. The damages we will notice in the field during the growing season are mainly: premature leaf drop, twig and stem dieback , bark necrosis and stem deformation.

Effects of diseases
Both leaf rust and stem infestation reduces production to various degrees depending on the level of infestation intensity. Stem canker and tip dieback impede transport within the plant and will also lead to excessive branching in willows, which is a serious drawback particularly in the production of cuttings. Poplars are more suffering from bacteria and fungi causing stem canker and wounds, which might increase the risk for stem breakage.

The leaf rust impairs photosynthesis, which especially during summer can result in significant loss of production. An attack later in the fall disrupts the plant winter dormancy, which might lead to frost damages and subsequent stem infestation during the winter. 

Extensive shoot dieback in a willow plantation the year after a severe rust attack followed by secondary fungal infections and frost. Photo: B. Samils

Managing measures
For development of stem damages, planting location and managing appear to be crucial parameters. Poor weed control with dense weed vegetation maintain high moisture and provides favorable environment for both fungi and bacteria, especially for willows densely planted. It also forms an inviting winter habitat for voles which has been found able to kill a complete plantation by feeding on the bark.

The survival prognosis is, however, generally good for willows, even where we experience dieback of the entire main shots during the autumn and winter. New shoots will protrude from the ground the following year if the roots are still alive and the weeds are kept back.

Strategy for future facilities
For a successful crop with high yield and long-term survival, a number of different clones should be used in a plantation rather than a single one. Different types of clone mixtures could prove to be the most appropriate approach for this purpose. Pathogenic organisms have a rapid adaptation and selection ability and poplars and willows aimed for good production for 20 years or more, could be a very vulnerable crop with the wrong measures.

(More information about damage and pests will soon appear on this page.)