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 relatively uneventful week for plant diseases, with few confirmed diagnoses. Many oak samples tested for oak wilt came back negative. However, a few notable cases stood out:
- Black Spot on Rose: A classic case caused by the fungus Marssonina rosae, easily identified by its distinctive curved, two-celled spores.
- Pear Scab: Observed primarily on fruit, leading to cracking and deformities. Sporulation was evident, though leaf loss was minimal.
- Phytophthora Root Rot: Diagnosed on phlox from a nursery—an uncommon setting for this pathogen.
- Pythium Root Rot: Found on other plant samples.
- Transplant Stress: A recurring issue, with one case involving a recently transplanted plant surrounded by rock mulch. Contributing factors included retained burlap and wire basket, and inadequate watering.
Additional Plant Disease Resources
- Black Spot – UW Plant Disease Factsheet
- Apple (Pear) Scab – UW Plant Disease Factsheet
- Root and Crown Rots – 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 seasonal shift in insect activity, with fewer landscape-related cases and more structural pest inquiries. Key highlights included:
- Fall Webworm: Still active and widespread this season.
- Lace Bugs: Continued activity, especially on oaks and hawthorns.
- Monarch Butterflies: Encouraging reports of sightings during migration, likely aided by summer rains.
- Fruit Pests: Ongoing homeowner concerns about fruit deformities caused by:
- Plum curculio
- Apple maggot
- Codling moth
- Grape phylloxera
- Parasitized Hornworms: Notable photos of hornworms with Cotesia wasp cocoons.
- Orb Weavers: Increased spider ID requests, especially for conspicuous species like the black-and-yellow garden spider (Argiope spp.).
- Asian Lady Beetles & Western Conifer Seed Bugs: Active around homes in northern Wisconsin.
- Tiger Mosquitoes: Public concern driven by news reports. Though present in Wisconsin since 2017, they are not established due to cold winters. Disease risk remains low.
- Large Mosquitoes: Reports of the “gallinipper” (Psorophora ciliata)—a large, native mosquito species following recent flooding.
- Kissing Bugs & Chagas Disease: No verified sightings in Wisconsin. Disease risk is extremely low. Increased public concern has led to misidentification of native assassin bugs, which are harmless and beneficial.
Additional Note: PJ advised against fall spraying for asparagus beetles, recommending sanitation instead.
Additional Insect Pest Resources
- Apple Maggot – UW Horticulture
- Asparagus Beetle – UW Horticulture
- Codling Moth – UW Horticulture
- Common Milkweed Insects – UW Horticulture
- Fall Webworm – UW Horticulture
- Garden Spiders – UW Horticulture
- Multicolored Asian Lady Beetle UW Horticulture
- Plum Curculio – UW Horticulture
- Western Conifer Seed Bug – UW Horticulture
