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 quieter week due to the holiday, but shared several notable cases:
- Fernleaf Buckthorn: Diagnosed with crown rust. Symptoms included dieback, branch galls, and sporulation of the causal fungus on leaves and stems. Brian reiterated that this buckthorn cultivar is not truly sterile and can contribute to spread of buckthorn, an invasive plant.
- Ornamental Cherry: Diagnosed with bacterial canker (caused by Pseudomonas syringae), identified by sap blobs on dying branches.
- Crabapples: Multiple samples showed branch dieback likely due to winter injury, with some fungal cankers (Diplodia, Cytospora, Phomopsis) and fire blight also confirmed in some samples.
- Ninebark: Powdery mildew found on fruit of a green-foliaged variety—unusual compared to more typical powdery mildew issues on red-leafed cultivars.
- Smoke Bush: Diagnosed with Verticillium wilt. Brian noted unusually sparse fungal growth in culture, which is atypical for the pathogen (Verticillium) involved.
- Virginia Wild Rye: Sample showed stripe smut caused by Ustilago nunavutica (confirmed via DNA sequencing).
- Strawberries: Crown and root rot caused by Phytophthora. Brian warned of long soil persistence of this pathogen and limited replant options.
- Needled Ornamentals: Winter burn symptoms on arborvitae and junipers continue to appear.
- Watermelon Seedlings: Yellowing and poor growth linked to allelopathy and nitrogen tie-up from recently tilled rye cover crop.
- Parsley: Bacterial leaf spot caused by Xanthomonas [confirmed via polymerase chain reaction (PCR)].
Weekly Insect Pest Summary
By PJ Liesch, UW Insect Diagnostic Lab Director
Website: insectlab.russell.wisc.edu
PJ Liesch shared a wide-ranging update:
- Japanese Beetles: Emergence confirmed in southern Wisconsin. Activity is currently low, but PJ is monitoring for increases. He highlighted sightings of the Winsome Fly, a parasitic fly that lays eggs on beetles’ pronotum and may help suppress Japanese Beetle populations.
- Asiatic Garden Beetle: Active in Dane and Green Lake Counties. Adults are nocturnal and highly attracted to lights. PJ encouraged reporting suspected sightings to him at the UW Insect Diagnostic Lab.
- Lily Leaf Beetle: New county records in Dunn and Adams Counties bring the total to ~30 counties statewide.
- Zimmerman Pine Moth: Confirmed with live caterpillars from Brian’s lab—the larvae are not commonly seen.
- Lace Bugs: Active on hawthorn, crabapple, and fruit trees. PJ described their speckled leaf damage and ornate appearance.
- Fruit Crop Pests: Codling moth and plum curculio are damaging apples and plums. Lots of secondary pest activity such as sap beetles on damaged or compromised fruits.
- Vegetable Crop Pests: Purple carrot-seed moth and black swallowtail caterpillars were found on dill.
- Turfgrass Pests: Black turfgrass ataenius larvae confirmed in Fort Atkinson. This is an occasional pest of manicured turfgrass such as golf course fairways. PJ distinguished them from annual bluegrass weevil.
- Other Sightings: Stag beetles, hermit flower beetles, box elder bugs, carpenter ants, and cicada killer wasps are active. PJ also addressed public concern over Asian longhorn beetles and Asian needle ants, confirming no current threats in Wisconsin.
Additional Insect Pest Resources
- Black Swallowtail – UW Horticulture
- Boxelder Bug – UW Horticulture
- Carpenter Ants – UW Horticulture
- Cicada Killer Wasps – UW Horticulture
- Codling Moth – UW Horticulture
- Japanese Beetles – UW Horticulture
- Lily Leaf Beetle – UW Horticulture
- Plum Curculio – UW Horticulture
- Zimmerman Pine Moth – UW Horticulture
