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Nursery & Forest
Volume 63 Number 4 Date 05/24/2018 BLACK SPOT ON ROSE - Symptoms of this fungal disease were observed on the hybrid rose cultivar 'Top Gun' at a nursery dealer in Dane County. Diagnostic features are small, round black spots with feathery margins on the leaf surface that enlarge and cause foliage to turn yellow and drop prematurely. The fungus overwinters on leaf and cane litter infected the previous season, and the fungal spores spread during wet weather to initiate disease development on new growth. There are many rose cultivars that are resistant to this disease, such as the hybrid (Rosa chinensis x R. multiflora) 'Desmond Tutu'. Cultural management techniques include removal of diseased debris and avoidance of splashing water on the foliage. Approved foliar fungicide applications may be applied prior to disease development. POWDERY MILDEW - Dahlia plants in a greenhouse in Vernon County were infected with this very common fungal problem of ornamentals, characterized on most plants by its grayish white powdery dusting on the upper leaves. This disease is favored by high humidity and wet weather. Reducing humidity levels and increasing air circulation will help to alleviate the problem. Fungicidal control is usually not necessary as this disease is largely a cosmetic concern. POTYVIRUS - An undetermined potyvirus was confirmed in spiderwort plants from nursery dealers in Washington and Kenosha counties. The symptom noticed by inspectors was severe light-green mottling on the foliage. Plant viruses may reduce plant vigor and spread to other plants of the same or different species. It is imperative to remove and destroy all virus-infected plants. NR-40 INVASIVE SPECIES RULE - As of 2018, the phase-out period for selling herbaceous plants classified as 'restricted' in Wisconsin, has ended. DATCP inspectors recently found the restricted plant moneywort (green-leaved cultivar) at nursery dealers in Brown and Sawyer counties. Nursery managers are reminded to review the NR40 list of invasive species before purchasing plants, as restricted species will need to be removed and destroyed. Although the phase-out period for herbaceous plants classified as 'restricted' has ended, the phase-out period for shrubs and trees does not end until 2020. -- Shanon Hankin, DATCP Nursery Inspector 
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