Disease identification
A working reference for the diseases that trouble roses in humid Texas. Symptoms, progression, the conditions that favor each pathogen, and a treatment ladder from cultural to organic to chemical. Updated as Birgit catalogs new symptoms in the garden.
What are you seeing?
Tick what you actually observe in the garden. We'll re-rank the diseases below by how well they match. Pick a few — three or four is usually enough.
Severe & high
Black Spot
Diplocarpon rosae (Marssonina rosae)
The most damaging rose disease in humid climates. Round black spots with feathery edges; leaves yellow and drop. Texas humidity makes it relentless.
Powdery Mildew
Podosphaera pannosa
Talcum-like white coating on new growth and buds. Looks like the rose has been dusted with flour. Loves dry days and humid nights.
Downy Mildew
Peronospora sparsa
A different and more dangerous disease than powdery mildew. Purple-red blotches with yellowing; rapid leaf drop in cool, wet spring weather.
Rose Rosette Disease
Rose Rosette Virus (Emaravirus); vectored by the eriophyid mite Phyllocoptes fructiphilus
The most serious rose disease in North America. Distorted growth, witches' broom, hyper-thorny canes. Currently no cure — infected plants must be removed.
Botrytis Blight (Gray Mold)
Botrytis cinerea
Buds that "ball" — fail to open and rot brown — and a fuzzy gray mold on dying flowers in cool wet weather.
Rose Rust
Phragmidium spp.
Bright orange pustules on the underside of leaves. More common in cool coastal climates than humid Texas, but still occasional.
Crown Gall
Agrobacterium tumefaciens (now Rhizobium radiobacter)
Tumor-like swellings at the base of the plant or on roots. A bacterial cancer that compromises the bush from below.
Stem & Cane Cankers
Coniothyrium spp. (Brand Canker, Common Canker, Brown Canker)
Sunken, discolored patches on canes that girdle and kill from the canker outward. The reason a perfect-looking cane suddenly wilts in midsummer.
Verticillium Wilt
Verticillium dahliae
A soil-borne fungus that clogs the vascular system. Sudden one-sided wilt on a hot day; brown streaking inside cut canes.
Phytophthora Root Rot
Phytophthora spp. (often P. cactorum, P. cinnamomi)
A water-mold root rot that kills roses in poorly drained soil. Sudden wilt and decline in spite of "plenty of water".
Moderate
Rose Anthracnose
Sphaceloma rosarum
Small, sharp-edged spots that drop out of the leaf, leaving a "shothole" pattern. Often confused with mild black spot.
Rose Mosaic Virus Complex
Prunus Necrotic Ringspot Virus (PNRSV); Apple Mosaic Virus (ApMV); others
Yellow patterning on leaves — rings, oak-leaf shapes, or yellow veins — that varies with weather. Once present, it is permanent.
Treatments listed organically before chemically. As an experienced grower, Birgit will know when each rung of the ladder is appropriate. When in doubt, the Texas A&M AgriLife Extension office and the American Rose Society Consulting Rosarians are excellent second opinions.