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Nursery & Forest
Volume 65 Number 12 Date 07/23/2020 REDHEADED FLEA BEETLE - These shiny black beetles with prominent reddish heads were prevalent on a wide variety of nursery plants in the past week. Defoliation caused by flea beetle feeding varies by leaf type, appearing as skeletonizing or shredding on thinner leaves and a linear, leafminer-like pattern on the thicker, fleshy leaves of sedum and similar plants. Beetle injury may reduce the aesthetic quality and marketability of stock, but insecticides directed against the adults should only be considered for severe cases. A few cultivars highly susceptible to RHFB damage include Virginia sweetspire 'Little Henry,' hydrangea 'Vanilla Strawberry' and 'Bobo,' red osier dogwood 'Kelseyi,' and weigela 'Fine Wine.' 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, 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 impacted 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. 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 southern and western Wisconsin. 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. Growers who experience problems with tar spot this year should mark their calendars to consider treatment next year. NINEBARK LEAF BEETLE - Adults were observed on ninebark plants in Waukesha County nursery last week. The distinctive reddish brown beetles with ornate black and gold markings are present from July to August and may feed heavily on ninebark foliage. Healthy plants can usually tolerate the feeding, and treatment of this native leaf beetle species discouraged. -- Shanon Hankin and Tim Boyle, DATCP Nursery Inspectors SPINY WITCHHAZEL GALL APHID - DATCP inspectors found these aphids on river birch at a nursery in Marinette County. The eggs of the witchhazel gall aphid overwinter on witchhazel, then hatch and feed on the flower buds, forming a spiny gall, before migrating to river birch. Feeding by the female aphids on birch foliage causes the leaves to pucker and become corrugated in appearance. Birch leaves often turn yellow and may drop prematurely. The aphids, which are covered in a white, waxy coating, live on the underside of these distorted leaves. If aphid populations are high, a fall soil drench of a systemic insecticide such as imidicloprid may be applied to the infested birch tree. -- Jen Oestreich, DATCP Nursery Inspector 
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