The extensive damage to elms by Dutch elm disease agents and their hybrids in northwestern Russia

Abstract

Elms are important amenity trees in the European part of Russia, incl. the St. Petersburg and Leningrad Region. The native species Ulmus glabra and U. laevis mainly grow there, on the northern border of their natural range. Hybrid elm cultivars have been planted since the early 2000s. Thousands of elms suffer from Dutch elm disease in the Leningrad Region. We found that in the north-western part of Russia Ophiostoma novo-ulmi subsp. novo-ulmi and O. novo-ulmi subsp. americana as well as hybrids of these subspecies are aggressive agents of DED on elms. According to in vitro experiments of hybrids in pure cultures, O. novo-ulmi subsp. americana x novo-ulmi had the highest growth rate, and O. novo-ulmi subsp. novo-ulmi the lowest growth rate.Ulmus glabra (>40 years old) was affected the most, with ca. 20 % of assessed trees found to already be dead and only 56 % found to be in good condition. The documented health among young elm cultivars (<25 years old) revealed that only 4% were dead, and 91 % were healthy or only experiencing some branch loss. Ulmus laevis (with 74 % of individuals healthy or with some branch loss, and 5% dead) was significantly healthier compared to U. glabra. In the city, the health of all assessed elm species was significantly better in greenspaces than next to highways.As the potential vectors of DED, Scolytus scolytus, S. multistriatus and S. pygmaeus are registered in the assessed region.