The fungus Stagonosporopsis citrulli has been detected in a watermelon crop at Mareeba in Queensland. Until recently, the fungus Didymella bryoniae was thought to be the sole cause of gummy stem blight (GSB). Now three morphologically similar species, Stagonosporopsis cucurbitacearum (synonym Didymella bryoniae), Stagonosporopsis citrulli and Stagonosporopsis caricae, have been recognised as causing GSB.
Symptoms are leaf spots, internal fruit rot and gum oozing from plant stems, hence the common name ‘gummy stem blight’.
The detection occurred as a result of relatively new molecular identification techniques. Stagonosporopsis citrulli is known to affect Citrullus species (e.g. watermelon), Cucumis species (e.g. cucumber, honeydew melon, rockmelon), and occasionally on Cucurbita species (e.g. pumpkin, squash, zucchini).
The Consultative Committee on Emergency Plant Pests (CCEPP) has agreed that this fungus is not an Emergency Plant Pest (EPP) under the Emergency Plant Pest Response Deed and likely to have been present for some time. Some records from Queensland under the names of similar species have now been shown to be Stagonosporopsis citrulli.
Growers are encouraged to maintain good on-farm biosecurity and continue with current control practices such as crop rotation, applications of fungicides and the destruction of crop debris.
About gummy stem blight
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.
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 can spread in the wind and splashing water. Warm and wet weather favours the disease.
Control options include the use of healthy planting material; rotating cucurbits with other non-cucurbit crops on a two-year cycle; correct application of the recommended fungicides, particularly if wet weather occurs; and the destruction of all organic debris from previous cucurbit crops by deep ploughing to reduce sources of inoculum from carrying over to new plantings.
Growers are reminded that a disease survey is being conducted by the melon industry. Access the survey here. Note: this survey is for growers only.
Industry Development Manager
Australian Melon Association Inc
Mobile: 0413 101 646