Synonyms: Peronospora geranii, Peronospora nivea, Rhysotheca geranii.
Plasmopara geranii is a downy mildew fungus that infects plants in the Geraniaceae family. In East and Central Texas, it has been found to primarily affect geranium and pelargonium species. The fungus produces yellowish or whitish sporangiophores on the underside of leaves, with corresponding yellow or chlorotic spots on the upper surface. It thrives in warm and humid environments, typically between 64°F and 90°F, and is often spread by wind-borne spores or contaminated water. Infected plants may exhibit stunted growth, leaf distortion, and premature defoliation.
Underside of a leaf of crane's bill (Geranium carolinianum) with white web-like downy mildew fungus Plasmopara geranii or may be P. pusilla on a trailway near Birch Creek Unit of Somerville Lake State Park. Texas, March 5, 2023
Burleson County, Texas, United States
Leaves of crane's bill (Geranium carolinianum) with white web-like downy mildew fungus Plasmopara geranii or may be P. pusilla on a trailway near Birch Creek Unit of Somerville Lake State Park. Texas, March 5, 2023Burleson County, Texas, United States
Spores (in KOH, x40 objective) of downy mildew fungus Plasmopara geranii or may be P. pusilla from a leaf of crane's bill (Geranium carolinianum), collected near Birch Creek Unit of Somerville Lake State Park. Texas, March 5, 2023
Conidiophores and conidia of downy mildew fungus Plasmopara geranii or may be P. pusilla from a leaf of crane's bill (Geranium carolinianum), collected near Birch Creek Unit of Somerville Lake State Park. Texas, March 5, 2023
Conidiophores and conidia (x100 objective) of downy mildew fungus Plasmopara geranii or may be P. pusilla from a leaf of crane's bill (Geranium carolinianum), collected near Birch Creek Unit of Somerville Lake State Park. Texas, March 5, 2023
Conidiophores and conidia (in lugol, x40 objective) of downy mildew fungus Plasmopara geranii or may be P. pusilla from a leaf of crane's bill (Geranium carolinianum), collected near Birch Creek Unit of Somerville Lake State Park. Texas, March 5, 2023
Conidiophores (in lugol, x100 objective) of downy mildew fungus Plasmopara geranii or may be P. pusilla from a leaf of crane's bill (Geranium carolinianum), collected near Birch Creek Unit of Somerville Lake State Park. Texas, March 5, 2023
Conidiophores and conidia (in lugol, x100 objective) of downy mildew fungus Plasmopara geranii or may be P. pusilla from a leaf of crane's bill (Geranium carolinianum), collected near Birch Creek Unit of Somerville Lake State Park. Texas, March 5, 2023
Conidiophores and round conidia of downy mildew fungus Plasmopara geranii or may be P. pusilla from a leaf of crane's bill (Geranium carolinianum), collected near Birch Creek Unit of Somerville Lake State Park. Texas, March 5, 2023
Downy mildew fungus Plasmopara geranii on leaves of cranesbill (Geranium carolinianum) in Lick Creek Park. College Station, Texas, December 15, 2023Iron Bridge Trail, College Station, Brazos County, Texas, United States
White mold like fungus Plasmopara geranii on underside of leaves of cranesbill (Geranium carolinianum) in Lick Creek Park. College Station, Texas, December 15, 2023Iron Bridge Trail, College Station, Brazos County, Texas, United States
Sporangiophores of downy mildew fungus Plasmopara geranii from leaves of cranesbill at low magnification, collected in Lick Creek Park. College Station, Texas, December 15, 2023
Sporangiophores and conidia of downy mildew fungus Plasmopara geranii from leaves of cranesbill at low magnification, collected in Lick Creek Park. College Station, Texas, December 15, 2023
Branches of sporangiophores with obtuse tips and oospores of downy mildew fungus Plasmopara geranii from leaves of cranesbill, collected in Lick Creek Park. College Station, Texas, December 15, 2023
White mold like fungus Plasmopara geranii on underside of leaves of cranesbill (Geranium carolinianum) on a lawn near Nature Center in Lick Creek Park. College Station, Texas, December 23, 2023Iron Bridge Trail, College Station, Brazos County, Texas, United States
Downy mildew fungus Plasmopara geranii on leaves of cranesbill (Geranium carolinianum) on a lawn near Nature Center in Lick Creek Park. College Station, Texas, December 23, 2023Iron Bridge Trail, College Station, Brazos County, Texas, United StatesIn East and Central Texas, observations of the fungus Plasmopara geranii were made on crane's bill (Geranium carolinianum) plants. The fungus was found to produce white, web-like downy mildew on the underside of leaves. Microscopic examination revealed conidiophores and conidia, with some samples showing round conidia. The fungus was observed in various locations, including Somerville Lake State Park and Lick Creek Park in College Station. In December 2023, observations in Lick Creek Park showed the fungus producing sporangiophores with obtuse tips and oospores. The fungus was also found on lawns near the Nature Center in Lick Creek Park, indicating its presence in different environments. Overall, the observations suggest that Plasmopara geranii is present in East and Central Texas, infecting crane's bill plants in various locations.
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