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Nursery & Forest
Volume 64 Number 14 Date 08/01/2019 LEAF SCORCH - Many varieties of nursery plants statewide are exhibiting leaf scorch brought on by the stresses of extended retail display, container compaction, nutrient deficiency, and extreme heat, drought, and over watering. This disorder is characterized by the browning of leaf margins and yellowing or darkening of the tissues between the primary veins. Most affected plants will generally recover once the stress factors have been resolved. However, in retail situations, non-viable ornamental plants and trees that have been reduced beyond reversible levels of physiological damage, have regulated pest or disease infestations, or fail to reach acceptable standards of cleanliness, labeling, and plant quality, must be removed from sales areas. PLANT VIRUSES - Plant viruses continue to be a persistent issue reported by inspectors at both grower and dealer locations. Recently, potyvirus was confirmed among the Iris cultivars 'Sweet Iris', 'Earl of Essex', and 'Tennison Ridge' in Dunn and Waukesha counties, in addition to solid green hosta hybrids at an Eau Claire County grower. A sample of the astilbe cultivar 'Fanal' (Astilbe x arendsii 'Fanal') from a Waukesha County nursery dealer was diagnosed with a form of Ilar virus, and a hosta hybrid from a Vilas County landscaping business tested positive for hosta virus X (HVX). Samples of the hosta hybrid 'Atlantis' from a Polk County nursery were also confirmed with HVX and tomato spotted wilt virus. Plant viruses cannot be directly controlled with chemical products. Depending upon the virus disease, control options for reducing virus transmission may include biological or chemical control of the insect vector(s), preventing viral introductions into uninfected stock, sanitary removal and disposal of infected plant materials, consumer education toward recognizing plant virus symptoms, and industry-wide efforts aimed at virus-resistant breeding and implementation of higher virus-free certification standards. An extensive image gallery of nursery plant virus symptoms compiled by the DATCP Plant Industry Lab can be found at: https://datcp.wi.gov/Documents/PlantVirusSymptoms.pdf. MAPLE LEAF TAR SPOT - Early signs of this normally late-season leaf blight disease of maple were observed this week on Freeman and Norway maples in Oneida and Jackson counties. Symptoms first appear as pale yellow, raised spots on the upper leaf surfaces that later develop into distinctive black, tar-like lesions. Tar spot of maple is usually an aesthetic disorder, but the noticeable leaf lesions can affect the marketability of landscape trees. For severe cases that warrant treatment, three fungicide applications are necessary for control: at bud break, when the leaves are half expanded, and when the leaves become fully expanded. Clearing and disposing of all infected leaves in fall is essential where tar spot is a recurring problem. LILY LEAF BEETLE - UW Entomologist PJ Liesch has confirmed the presence of lily leaf beetle (LLB) in Dane and Door counties. First reported in Marathon County in 2014, LLB has now been detected in 10 Wisconsin counties. The adult beetles are bright red and conspicuous, while the larvae are usually noticed after Asiatic lily leaves become defoliated. Lily leaf beetle feeding damage can be severe and, without intervention, is eventually lethal to plants. Recommended controls include manually removing and killing adults and larvae, scraping eggs from the undersides of leaves, or applying an insecticide labeled for use on ornamentals. Nurseries, gardeners and property owners in Dane and Door counties are advised to be on the lookout for this pest. -- Tim Boyle, DATCP Nursery Inspector 
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