Citrus
Melanose
Diaporthe citri
Fungus
In a Nutshell
- Small brown discrete spots appear on leaf about one week after infection. Dark colored raised pustules appear after leaf infection, and are surrounded by yellowed leaf tissue or yellow halos.
Can also be found in
Citrus
Symptoms
Melanose symptoms occurs as reddish-brown to dark-brown specks (0.2 - 1.5 mm in size) on fruits at the late stages of maturation. The specks form around the oil glands present on the skin. Wound tissue and cracking is common in the process of infection. Fruits may be stunted and fall prematurely. Contrarily to similar spots caused by other diseases, melanose spots have a sandpaper-like texture when touched. On fully mature fruits the pathogen causes fruit rot, which typically develops from the stalk and may also cause early fruit fall. Foliar symptoms appear first as small brown discrete spots that later develop into raised pustules impregnated with a reddish-brown gum. They are often surrounded by a yellow halo, eventually forming small, hard corky pustules. Under storage conditions, stem-end rot may occur.
Recommendations
Organic Control
Use sprays containing organic copper compounds to treat D. citri. Initial application should take place at petal fall, followed by a secondary treatment 6-8 weeks later.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. Applications of pyraclostrobin during the spring flush growth has been proved effective against the development of melanose on fruits. Products based on mancozeb and fenbuconazole are also recommended. Strobilurin fungicides have also given satisfying results and may also be applied.
What caused it?
Melanose is a decomposing organism, that completes its life cycle on dead twigs. The severity of the disease is determined by the amount of fungal growth on dead wood and the duration of continuous wetting periods following rainfall or overhead sprinkler irrigation. Around 18-24 hours of wetting and temperatures between 20-24 °C are required for infection to occur. Spores cause problems when there are significant amounts of dead wood on trees, on the ground or in piles of brush left in the grove.
Preventive Measures
- Remove dead tree material regularly in the orchard.
- Prune the trees 1-2 times per year of damaged or dying parts.
- Ensure a balanced fertilization for the trees to improve the physical resistance to the pathogen.
- Monitor regularly for symptoms of the disease.
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