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Plantwise Technical Factsheet

black spot of elm (Stegophora ulmea)

Host plants / species affected
Ulmus (elms)
Ulmus alata (Winged elm)
Ulmus americana (American elm)
Ulmus crassifolia (Cedar elm)
Ulmus davidiana (japanese elm)
Ulmus glabra (mountain elm)
Ulmus hollandica (hybrid elm)
Ulmus laciniata
Ulmus laevis (Russian white elm)
Ulmus minor (European field elm)
Ulmus parvifolia (lacebark elm)
Ulmus procera (english elm)
Ulmus pumila (dwarf elm)
Ulmus rubra (slippery elm)
Ulmus serotina (red elm)
Ulmus thomasii (rock elm)
Zelkova serrata (Japanese selkova)
List of symptoms/signs
Fruit  -  abnormal shape
Leaves  -  abnormal colours
Leaves  -  abnormal leaf fall
Leaves  -  abnormal patterns
Leaves  -  necrotic areas
Stems  -  dieback
Symptoms
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.
Prevention and control
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.

Chemical Control

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:

Phytosanitary Measures

S. ulmea was added to the EPPO A1 action list in 2003, and endangered EPPO member countries are thus recommended to regulate it as a quarantine pest. It is suggested that plants for planting of Ulmus should be dormant and free from leaves, and either originate from a pest-free area, or else from a pest-free place of production where the plants were fungicide-treated.
Impact
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.
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