EPPO Pest Risk Analysis for Thekopsora minima (Fungi: Pucciniastraceae)
The areas more at risk would be those where evergreen Vaccinium are grown and T. minima may overwinter and continue its cycle outdoors in the absence of Tsuga, as well as areas of extensive cultivation of hosts under protected conditions. Areas with wet conditions during the growing season might be especially at risk. T. minima may also have a higher impact where Tsuga (e.g. private gardens and parks) and especially where it is frequent (i.e. close to plantations).
Overall assessment of risk: The risk of entry of T. minima into the EPPO region is mostly linked to the trade of Vaccinium plants for planting. T. minima is a serious pest in some countries. In the EPPO region, the disease has a limited distribution in the Netherlands and is under eradication in several others countries.
T. minima would have impact on cultivated North American blueberries, which is an expanding crop in the EPPO region. It is likely to spread naturally and through the trade of Vaccinium plants for planting. Damage is expected to be more severe in areas with sufficient humidity and where evergreen Vacciniums are grown, while in general it would mostly present a problem for nurseries. In areas where Tsuga occurs, these may increase the build-up of inoculum, spread and impact of T. minima. The wild Vaccinium species in the EPPO region are currently not known to be hosts, but damage may be higher if they are. The Panel on Phytosanitary Measures emphasized that eradication of rusts is very difficult, and that NPPOs should aim at preventing the introduction of the fungus. T. minima still has a very limited distribution at the scale of the EPPO region, and although it will spread naturally, such spread will be slow at the scale of the region, and phytosanitary measures have to be strengthened to prevent its introduction into other EPPO countries. Trade of plants for planting is a major pathway and large quantities are traded from the USA and also within the EPPO region. Phytosanitary measures to reduce the probability of entry: Measures were recommended for the high risk pathway, i.e. Vaccinium plants for planting. Because T. minima has often been found in association with V. corymbosum and hybrids, measures on plants for planting of those, and possibly V. angustifolium and V. ashei, would be especially important. However, there is still an uncertainty about the host range. For Vaccinium fruit, even if the risk of entry if considered as very low, producers should be encouraged to not import bulk fruit to be repacked in their production units (or at least to manage any waste safely to avoid spread of spores).
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