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Initial diagnostic symptoms on elms are small yellow spots (1 mm diameter) which turn black as stromata develop, hence the common name 'black spot'. The black spots measure up to 5 mm in diameter. Other symptoms are premature shedding of leaves and, in a severe infection, blight of young leaves and shoots and complete defoliation by early August. Green fruits can become infected and crumpled. Disease symptoms can be observed throughout the year in species of evergreen elm.
Cultural Control and Sanitary Methods
Cultural control involves reduction of inoculum by removal of all leaf debris, which might be achieved in nurseries, or managed parks and gardens, but not in other situations. If leaf infection has already occurred, the pathogen can in any case survive in dormant buds. On nurseries where overhead watering is practised, cessation of such watering would reduce inoculum spread.
Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:
Black spot was the best known disease of elms in North America prior to the advent of Dutch elm disease, but the effects of infection are rarely fatal on mature elms and recovery has been observed even where repeated defoliation has occurred (Sinclair et al., 1987). In the 1930s, nursery stocks of young Ulmus americana in northern Illinois, USA, were severely damaged by infection by the fungus in combination with 'Gloeosporium inconspicuum'. The worst damage was attributed to 'G. inconspicuum' (Trumbower, 1933). S. ulmea can cause significant defoliation and twig dieback on susceptible elm cultivars in nurseries.