Nursery & Forest
Volume 63 Number 6 Date 06/07/2018
FLETCHER SCALE ON YEW - A moderate infestation of adult female scales was found on 'Capitata' upright yews at a nursery dealer in Dunn County. The female's hard shell conceals up to several hundred immature "crawlers," which will likely emerge very soon. Insecticides cannot penetrate the hard shell covering and should be applied when the crawlers are noticed. This pest of arborvitae, juniper and yew can cause yellowing, premature needle drop or branch dieback. For severe infestations, horticultural oils or soaps, insect growth regulators or conventional insecticides may be used. DATCP nursery inspectors are advising retailers not to sell evergreens infested with this scale species.
-- Konnie Jerabek, DATCP Nursery Inspector
DOWNY MILDEW - Downy mildew was observed on butterfly bush shrubs at a nursery dealer in Dane County. The surface of the leaves were showing brown necrotic areas, while the undersides had the characteristic fungus-like mycelium (downy mildew is not a true fungus, it is in the water mold family). Downy mildew usually develops on plants during periods of cool, wet weather. To best manage and prevent this disease, controlling humidity levels, spacing plants to increase air circulation, and removing diseased tissue are recommended. Application of approved fungicides may be warranted in some situations.
PHYTOPLASMA IN ECHINACEA AND COREOPSIS - Phytoplasma infections were diagnosed in echinacea and coreopsis plants from Walworth County. Phytoplasmas were discovered in 1967 but remain puzzling as they are challenging to detect in the laboratory and little is known regarding their lifecycle. Phytoplasmas are bacterial-like prokaryotic organisms that infect the phloem in plants and are spread by phloem-piercing insects such as leafhoppers and psyllids. These organisms are thought to alter gene expression, often causing irregular growth patterns. They are also thought to cause yellowing in plant tissue. Ash yellows is a well-known phytoplasma disease of ash trees which causes gradual crown deterioration and brooms that often develop at the base of the tree.
-- Shanon Hankin, Marcia Wensing and Reba Gruber, DATCP Nursery Inspectors
ROSE SLUG - The tiny green larvae of this sawfly were feeding on rose foliage in La Crosse County this week, skeletonizing the leaves. Severe defoliation may be avoided by removing the larvae and the damaged, lacy leaves. Horticultural oils or residual insecticides are also effective.
EMERALD EUPHORIA - Beetles were noted late last month on perennials in Dane County. This species (Euphoria fulgida) is considered common but not abundant in the state. UW Insect Research Collection records list it as occurring in Crawford, Dane, Door, Iowa, Iron and Monroe counties.
-- Krista Hamilton, DATCP Entomologist