The UW Lab Lens summarizes current pests, diseases, and problems occurring throughout Wisconsin to help you stay ahead of pests in your garden or landscape.
Weekly Plant Disease Update
By Brian Hudelson, UW Plant Disease Diagnostics Clinic Director
Website: pddc.wisc.edu
Brian Hudelson reported a surge in root rot diagnoses across a wide range of woody ornamentals, both deciduous and coniferous. The culprits include Phytophthora, Pythium, Fusarium, and Cylindrocarpon, with Phytophthora being the most aggressive. Saturated soils from recent rains are providing an optimal environment for root rots to develop.
- Herbaceous Ornamentals
- European Ginger: Diagnosed with white mold (Sclerotinia)
- Hosta:
- One sample tested positive for Hosta virus X.
- Another tested positive for Cucumber mosaic virus (aphid-transmitted).
- A third sample showed signs of Southern blight (tiny sclerotia were present on petioles).
- Spirea: Diagnosed with anthracnose.
- Willow: Also showing anthracnose symptoms.
- Conifers & Needled Woody Ornamentals
- Juniper & Limber Pine: Diagnosed with Diplodia shoot blight, which causes shoot dieback and can eventually kill infected plants if the causal fungus moves into the main trunk of trees or the crowns of shrubs.
- Spruce:
- Classic case of Cytospora canker (lots of bleeding on the infected branches with fruiting bodes of the causal fungus present).
- Also a case of herbicide damage (distorted growth).
- Deciduous Trees & Shrubs
- Pagoda Dogwood: Diagnosed with golden canker (Cryptodiaporthe canker) – golden branch tissue with orange spots (fruiting bodies of the causal fungus).
- Maple:
- Anthracnose present.
- Chlorosis symptoms likely due to manganese deficiency.
- Some leaves showed sunburn (blotchy brown areas).
- Oak:
- One confirmed case of oak wilt.
- Chlorosis likely due to iron deficiency.
- Vegetables & Fruit Crops
- Pepper: Charcoal rot (caused by Macrophomina phaseolina). This disease often is more common in hotter, drier environments.
- Tomato: Diagnosed with Herbicide Drift symptoms.
- Snap Bean: Diagnosed with Halo Blight (Pseudomonas syringae pv. phaseoli), a bacterial disease with large yellow halos around small necrotic spots.
- Apple: Cytospora Canker (fire blight ruled out).
- Other Diagnostic Notes
- Chlorosis: Differentiation between iron and manganese deficiencies is crucial; nutrient testing and soil pH analysis recommended.
- Dog Vomit Slime Mold: Found on onion stems – a curious but non-disease sample.
Additional Plant Disease Resources
- Anthracnose – UW Plant Disease Factsheet
- Chlorosis – UW Plant Disease Factsheet
- Cucumber Mosaic – UW Plant Disease Factsheet
- Cytospora Canker – UW Plant Disease Factsheet
- Diplodia Shoot Blight and Canker –
- Golden Canker – UW Plant Disease Factsheet
- Herbicide Damage – UW Plant Disease Factsheet
- Hosta Virus X – UW Plant Disease Factsheet
- Oak Wilt – UW Plant Disease Factsheet
- Root and Crown Rots – UW Plant Disease Factsheet
- Slime Molds – UW Plant Disease Factsheet
- Southern Blight – UW Plant Disease Factsheet
- White Mold – UW Plant Disease Factsheet
Weekly Insect Pest Summary
By PJ Liesch, UW Insect Diagnostic Lab Director
Website: insectlab.russell.wisc.edu
PJ Liesch noted a slight tapering of insect cases but highlighted several active pests:
- Lace Bugs – heavy activity on asters (chrysanthemum lace bug), oaks (oak lace bug), and hawthorns (hawthorn lace bug).
- Imported Willow Leaf Beetles – damaging willows, including weeping varieties.
- Dog-Day Cicadas – widespread and noisy, as expected this time of year.
- Cicada Killer Wasps, Great Black Wasps, and Great Golden Digger Wasps – active and hunting cicadas and other respective prey insects. Large, but generally harmless..
- Introduced Pine Sawfly – active on conifers; multiple generations per year.
- Elm Zigzag Sawfly – increasing reports statewide.
- Walnut Caterpillars – gregarious larvae molting on walnut trunks.
- White-Marked Tussock Moth – fuzzy caterpillars; avoid touching due to urticating hairs.
- Broad Mites – suspected on peppers; awaiting confirmation. When encountered, these are generally on plants that had originated in a greenhouse.
- Japanese Beetles – active in northern counties, feeding on grapes, apples, and landscape plants.
- Apple and Thorn Skeletonizer – minor leaf damage on apples; more curiosity than concern.
- Carpenter Bees – increasing sightings in southern Wisconsin; males are territorial but generally harmless.
- Butterflies & Moths – sightings include summer azure and the endangered Karner blue.
PJ also reminded the group to be on alert for Spotted Lanternfly emergence, especially in late summer and early fall.
Additional Insect Pest Resources
- Cicadas – UW Horticulture
- Cicada Killer Wasps – UW Horticulture
- Elm Zigzag Sawfly – UW Horticulture
- European Pine Sawfly – UW-Horticulture
- Insect Identification Tool: Pine Insects – UW Entomology
- Japanese Beetle – UW Horticulture
- Sawflies – UW Horticulture
- Spotted Lanternfly – UW Horticulture
- Wisconsin Bee Identification Guide – UW Horticulture
