Melanose: identify, prevent, control

Updated October 2026

Worst in wet springs and summers in Northland, Auckland, Bay of Plenty and Gisborne, while new leaves and young fruit are developing from October to February.

Melanose is a fungal disease of citrus that leaves small, raised, dark brown specks on fruit, leaves and young twigs. The fungus lives on dead twigs inside the tree, and rain splashes its spores onto new growth. It rarely harms the tree or the eating quality of the fruit, but heavily marked fruit looks rough and sandpapery.

Diaporthe citri

How to identify it

• You first notice tiny dark brown to black specks, about the size of a pinhead, scattered across young leaves and the skin of developing fruit.
• The specks are raised, so the surface feels rough like fine sandpaper when you run a finger over it.
• On leaves the specks sometimes start with a faint yellow halo that fades as the leaf hardens.
• Where rain or dew has run down the fruit, the specks can line up in streaks, a pattern growers call tear staining.
• Heavy infections join up into a cracked, crusty patch that looks like dried mud, which is called mudcake melanose.
• Look inside the canopy and you usually find dead twigs, because that is where the fungus breeds.

What it is often confused with

When and where it is worst

Melanose is most common where citrus grows best in New Zealand, in Northland, Auckland, the Bay of Plenty, Gisborne and warm parts of Hawke's Bay. Trees in humid, sheltered backyards with plenty of dead wood in the canopy are the most affected. Grapefruit, oranges, tangelos and pomelo tend to show it most, while lemons, limes, mandarins and cumquats can also carry the specks.

Spores are made on twigs that have died in the past few months and are spread by rain and irrigation splash. Leaves are only susceptible while they are young and soft, and fruit is at risk from petal fall for roughly two to three months. In most of the North Island that means spells of warm, wet weather between October and February cause the infections you see later in the season.

Plants it affects

These plants in our library list it as a problem to watch for.

How to prevent it

• Prune out dead and dying twigs every year, ideally in late winter or early spring before the main flush of growth, because dead wood is the source of the spores.
• Thin the inside of the tree a little so it dries quickly after rain and sun can reach the centre.
• Water at the base of the tree rather than over the canopy, so you are not splashing spores about.
• Rake up and remove prunings and fallen twigs rather than leaving them under the tree.
• Keep the tree well fed and watered through summer, since stressed trees die back more and create more dead wood.
• When you choose a new tree for a very wet spot, a lemon or mandarin usually copes better than a grapefruit or orange.

Organic control, step by step

• Start with hygiene, removing every dead twig you can reach and taking the prunings out of the garden.
• Open up crowded growth so the canopy dries out quickly after rain.
• In a wet spring, apply a copper spray at petal fall to protect the newly set fruit, since copper is allowed in organic growing in limited amounts.
• Repeat the copper about four to six weeks later if the weather stays wet, and stop once the fruit is about two to three months old, because older fruit is no longer infected.
• Accept light specking on home fruit, as it only affects the skin and the fruit is fine to eat or juice.

Conventional control

• Copper oxychloride or copper hydroxide applied at petal fall gives the best protection for young fruit, because sprays before flowering do not prevent fruit infection.
• Follow with a second copper spray about four to six weeks later in a wet season, and a third only if rain continues while fruit is still small.
• Cover new leaf flushes as well as fruit, spraying to the point of run-off on both sides of the leaves.
• Read the label before you buy or spray, check that citrus is listed, and keep to the withholding period before picking.

Frequently asked questions

Related problems

Sources: Chaisiri et al. 2022, Diaporthe citri: a fungal pathogen causing melanose disease, Plants (PMC); Royal New Zealand Institute of Horticulture, Plant Doctor: Scaly skinned citrus; NSW DPI, Melanose (citrus disease factsheet). Identification and control follow these sources. Always read the product label before use.