Jalakasurma levikust ja ohtlikkusest Eestis

Abstract This review provides an overview of and describes the current situation of Dutch elm disease (DED), which is one of the most devastating diseases for elms worldwide and in Estonia. It is known that in Estonia DED’s agent Ophiostoma ulmi has been damaging elms since the 1930s. Today a new species Ophiostoma novo-ulmi is considered to be an agent of DED. Since 2013 the current epidemic has been recorded in most of the counties of Estonia. The both known DED agents, Ophiostoma novo-ulmi subsp. novo-ulmi and O. novo-ulmi subsp. americana were molecularly detected on Ulmus spp. Additionally, one hybrid pathogen of the subspecies (americana x novo-ulmi) was identified in northern Estonia. Also, the health status of elms and the potential vector agents of the pathogen are discussed and recommendations for disease management are provided. Summary The threat to Ulmus spp. has risen in Estonia, apparently due to the trade of infected elm plants and changing climatic conditions having contributed to the invasion of new pathogens and their vectors. It is known that in Estonia Dutch Elm Disease (DED) has had a devastating impact on elms since the 1930s. Today its agent Ophiostoma ulmi has been replaced by a new, apparently an invasive species Ophiostoma novo-ulmi in most countries of Europe, as well as in Estonia. Since 2013 the health status of elms in Estonia has worsened substantially. The aim of this research was to analyse the current spread of DED until 2020, specify the taxonomy of pathogens, evaluate the health status of host plants, and analyse the control options of the disease. Visual assessment has been provided for the period of 2014 to 2020. Methods and results for the years 2014–2016 are presented in a previous paper (see Jürisoo et al., 2019). More precise monitoring of Dutch elm disease in Estonia started in 2014. A preliminary map of DED was provided on the basis of the assessments of the distribution (records). Thereafter, in the period of 2014–2020 more than 2,200 trees of genus Ulmus, mostly Ulmus glabra were assessed. Also, over 500 samples were collected of which 183 pure cultures of Ophiostoma novo-ulmi were isolated and analysed with different molecular primers (Table 3). In the period of 2018–2020, DED was detected in 14 counties of the total of 15 counties in Estonia. The analyses show that O. novo-ulmi subsp. novo-ulmi is widely spread; however, O. novo-ulmi subsp. americana was detected only in northern Estonia and on Hiiumaa island in western Estonia (Fig. 6). For the first time the hybrid pathogen (americana x novo-ulmi) was detected at a sampling site at Kose in northern Estonia (Figure 6). Our investigation demonstrated that in terms of the use of Ulmus as an amenity tree species Ulmus laevis could be considered more prospective than U. glabra because the health of U. laevis is significantly better and DED is not so devastating to the host. Also, we have to test resistant hybrid elms in our environmental conditions before starting massive planting in our green areas. All the plant material should meet the local standard on Quality Requirements for the Nursery Plants (see EVS 939-2, 2020). We have created several provenance trials in Estonia to qualify tolerant elm species or origins in the future. DED control is complicated because effective universal control methods are not available. Thus, a good sanitation program together with a reliable survey is needed. Symptomatic elms should be felled and completely destroyed; this seems to be the most effective method for DED control. Introduced planting material should be certified and controlled to minimise the invasion of diseases and pests.