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 shared a comprehensive update on plant disease diagnoses for the week of September 25. The following is a summary of notable cases:

Trees and Shrubs

• Frasier Fir: Diagnosed with Phytophthora root rot from nursery sample.
• Juniper: Tip dieback observed; likely due to transplant stress, improper planting (burlap left on), and over-fertilization.
• Oak: Leaf diseases including anthracnose (Discula), Tubakia leaf spot (Tubakia dryina), and Monochaetia leaf spot (Monochaetia sp.). Yellowing  and necrosis between veins observed, which is typical of severe chlorosis. No confirmed cases of Bur Oak Blight (Tubakia iowensis).
• Sweet Shrub: Diagnosed with Phytophthora root rot.
• Azaleas/Rhododendrons: Classic dieback symptoms with curled leaves; confirmed Phytophthora root rot.

Vegetables and Fruit Crops

• Apple/Crabapple: Marssonina blotch (Marssonina coronaria) observed on leaves. Fruit issues included flyspeck (Zigophiala jamaicensis) and sooty blotch (miscellaneous sooty blotch fungi). Physiological disorders such as water core, bitter pit, and cork spot also noted.
• Cherry: Cherry leaf spot caused by Blumeriella jaapii.
• Lima Beans: Diagnosed with bacterial brown spot (Pseudomonas syringae pv. syringae) and common blight (Xanthomonas axonopodis pv. phaseoli).
• Beets: Cercospora leaf spot (Cercospora beticola) identified by characteristic circular lesions with dark borders.
• Pumpkin: Plectosporium blight (Plectosphaerella cucumerina) diagnosed by spindle-shaped lesions and dense white sporulation.
• Squash: Squash mosaic virus confirmed via testing; symptoms included mosaic patterns and warts on fruits. Transmission likely via cucumber beetles and contaminated tools.

Other

• Artillery Fungus: Identified from spore packets found on plants and inanimate objects. Commonly grows in mulch. Recommendation: Routinely rake mulch to disrupt fruiting body formation.