Tuesday, 4 March 2019
Name: Gummy stem blight, Stagonosporopsis spp.
Symptoms on seedlings occur as light to dark brown spots on the cotyledons. Infection of the cotyledons or hypocotyl causes a water-soaked, brown discolouration of the tissues, followed by tissue desiccation and collapse. Seedlings die rapidly after infection of either the hypocotyl or cotyledons.
On older plants, leaf symptoms appear as small circular, tan spots up to 5 mm in diameter, sometimes surrounded by a yellow halo. Under favourable conditions, the leaf lesions may enlarge rapidly and become irregular in shape. When the lesions coalesce, the entire leaf may become blighted. The spots dry, become cracked and may tear, giving leaves a tattered appearance. Infection often begins at the leaf margins.
Stem infections consist of brown oblong water-soaked lesions. Main stem lesions enlarge and slowly girdle the main stem resulting in a brown canker that produces a characteristic red or brown gummy fluid. Tiny black pimple-like fruiting bodies of the fungus (pycnidia) develop within the infected tissue. Cankers can girdle the entire stem and result in foliage wilting and affected areas dying. Vine wilting is usually a late symptom of the disease.
The most important form of the disease is crown rot, which may kill plants. At first, pale brown, then bleached areas develop, and a reddish gum oozes from cracks. Fruit develop water-soaked, small oval to circular spots that are a greasy green colour and turn dark brown as the spots enlarge. Gummy exudate and black fruiting bodies may develop on the spots. Affected fruit may eventually become black in colour.
Transmission: The fungus is seed-borne and can survive in soil, weeds and on crop residues. The fungal fruiting bodies contain large numbers of spores that spread in wind and splashing water.
Favoured by: Warm, wet weather favours the disease.
Host range: Gummy stem blight is a major disease of cucurbits, particularly in tropical and subtropical areas. The disease can cause serious losses in watermelon, rockmelon, honeydew, squash, pumpkin and cucumber. It has also been reported from papaya. The classification of gummy stem blight has changed in recent years. There are now three species of gummy stem blight all in the genus Stagonosporopsis. Research indicates that all species can cause damage to all host plants species, at least under laboratory conditions.
If you suspect that you have detected this species contact your local biosecurity agency or the emergency plant pest hotline: 1800 084 881.
Note that the Pest ID tool is now available with free access to industry.
An initiative of the Nursery Levy funded National Nursery Industry Biosecurity Program (NY15004) and ‘Building the resilience and on-farm biosecurity capacity of the Australian production nursery industry’ Project (NY15002).