Wet Rot

Wet rot caused by the fungus Choanephora cucurbitarum occurs on both stock plants and on cuttings under mist propagation. The pathogen is capable of killing plants in all stages of production.

Wet rot caused by the fungus Choanephora cucurbitarum on stock plants.
Click on image for larger version. (image © Ron Jones, NCSU)

Wet rot caused by the fungus Choanephora cucurbitarum.
Click on image for larger version. (image © Ron Jones, NCSU)

The symptoms of wet rot on poinsettia plants are a soft, wet, mushy decay of leaves, petioles and stems. If the stems are green and actively growing, they become soft, wet, flaccid and wilt or droop before collapsing. If the stems are somewhat woody, only necrosis occurs. Small plants and rooting cuttings may be destroyed in only a few days when weather conditions are favorable for disease development. On large multi-stemmed stock plants, the fungus may kill the plant stem by stem.

The pathogen usually sporulates profusely on diseased plant parts, especially on stems. The fungus produces single-celled sporangiophores (stalks), each bearing a cluster of black spores on the end. The sporangiophores are long and very abundant, giving the appearance of a coarse, hairy or whiskery growth. The spores can be spread by water, wind, movement of plants (cuttings), hands, knives and insects.

This is primarily a disease of stock plants and cuttings under mist. This fungus attacks the flowers of a wide variety of plants including squash, okra, petunia and hibiscus.

The importance and stage for infection of poinsettia diseases.

Disease

(Common Name)

Pathogen

Importance in North Carolina¹

Occurrence²

Bacterial Canker

Corynebacterium poinsettiae

+

F

Bacterial Leaf Spot

Xanthomonas poinsettiicola

-

F

Bacterial Soft Rot

Erwinia carotovora

+++

P

Botrytis Blight (Gray Mold)

Botrytis cinerea

++++

S, P, F

Crown Gall

Agrobacterium tumefaciens

-

S

Crown Rot

Sclerotinia sclerotiorum

-

S, F

Greasy Canker

Pseudomonas viridaflava

-

S, F

Leaf Spot

Alternaria euphorbiicola

-

S

Powdery Mildew

Unidentified

+

S, P, F

Root Knot Nematode

Meloidogyne spp.

-

F

Root Rot

Pythium spp.

Phytophthora parasitica

Thielaviopsis basicola

++++

+

+

S, P, F

S, F

F

Rust

Uromyces euphorbiae f. poinsettiae

-

F

Scab

Sphaceloma poinsettiae

-

S, F

Stem and Crown Rot

Rhizoctonia solani

++++

S, P, F

Virus

Poinsettia mosaic virus

+

S, P, F

Watery Rot

Rhizopus spp.

++

S, P

Wet Rot

Choanephora cucurbitarum

++

S, P

¹ Relative importance in North Carolina: (++++) most important; (-) very rare or does not occur.

² Stage of production for infection: S=stock plants; P=Propagation; or F=Finish