Section outline
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Dutch elm disease (DED) is the most devastating disease for elms all over the world (Brasier 1991; Brasier and Webber 2019). Elms have experienced two pandemics – the first at the beginning of the 20th century when 10-40% of elms were killed (Peace 1960; Gibbs 1978; Brasier 1996a; Brasier 2000) and the second since the second half of the 20th century (Brasier and Buck 2001) when also billions of elms were killed (Phillips and Burdekin 1992; Herald 2019). By the beginning of the 21st century (Brasier and Buck 2001; Kirisits 2013) approximately 80-90% (28 million) of mature elms had died in the UK, as well as hundreds of millions in North America (Brasier 2001; Brasier and Buck 2001).
DED agent is known to kill trees rapidly, even during one or two seasons (Phillips and Burdekin 1992, Schmidt 2006). Mortality by DED varies according to the host (Ulmus) species and depends on the susceptibility and genetic variety (Martín et al. 2019), the stand density and possible rootgrafts (Santini and Faccoli 2013), as well as on the seasonality of the infection and stress factors like drought (Kirisits 2013); also, mortality is influenced by the pathogen´s spore concentration inside the tree (Flower et al. 2017).