The susceptibility of herbal willow to Melampsora rust and herbivores

Eight Dark-leaved willow ( Salix myrsinifolia ) clones and two naturally hybridised clones ( S. myrsinifolia × S. phylicifolia ), that are considered to be suitable for herbal production, were cultivated for 2 years in Luikonlahti and Punkaharju. Both experimental sites are located in eastern Finland and the distance between the sites is 140 km. Different cultivation methods were used, including combinations of soil tillage, plastic mulch and fertilisation, with the aim of comparing the growth and susceptibility of plants to pathogens and willow-eating herbivores amongst the clones cultivated by different methods. In both study years 2001 and 2002, Melampsora rust-infected willows occurred in Luikonlahti and in Punkaharju. The extent of rust severity varied greatly between the years and experimental areas and amongst the clones. In 2002, fertilisation increased rust severity in Luikonlahti, but the effect was the converse in Punkaharju. Mulch effect on rust severity was clone-dependent. Vole feeding was observed in 56% of the plants in Luikonlahti during the winter 2001–2002 and the frequency of damaged plants was nearly twice as much amongst the willows grown in unmulched soil as those with plastic mulch. Cultivation method had no effect on feeding by leaf beetles or the abundance of aphids. Of the cultivation methods tested here, plastic mulch seems to have the most important influence on willow cultivation, particularly by improving willow growth and also by decreasing winter-feeding by voles.