Copper completes the circle for Sigatoka control

Copper fungicide has travelled the complete circle in the control of Sigatoka disease on banana. Copper was the very first fungicide to be used against yellow Sigatoka over 60 years ago and is now back in contention and favour due to its broad spectrum activity and long history of use without resistance which now plagues many single-site action systemic fungicides.

Yellow Sigatoka (leaf spot) disease caused by Mycosphaerella musicola is long established, but the more recently occurring black Sigatoka (black leaf streak) disease caused by Mycosphaerella fijiensis is more aggressive and damaging. Yellow Sigatoka was first recorded in Java in 1902. By the late 1930's the disease was widespread in Central America and the Caribbean Islands where chemical control using copper fungicide began in earnest in the early 1950's, first with water-based sprays, using ground sprayers and later by aerial application as oil based sprays.

Sigatoka is a classic crop debilitating disease causing rapid destruction of leaf photosynthesis and accompanying catastrophic reductions in bunch weight and quality. Genomics of the genus Musa (banana) is extremely complex but as a general rule dessert bananas (AAA genome) are more susceptible than plantain bananas (AAB genome) and vegetable bananas (ABB genome). All are essentially susceptible to severe damage caused by M. fijiensis (black Sigatoka).

Black Sigatoka sets the agenda

A major milestone was discovery of the more aggressive black Sigatoka identified in 1963 on Fiji and named as such because of the dark brown or black streaks formed on the leaves. This aggressive disease quickly spread throughout Asia during the 1960's, into Africa and Central America by the early 1970's and into South America by the early 1980's.

In true tropical climates, leaf spotting appears 8 to 10 days sooner (after infection) for black Sigatoka than for yellow Sigatoka. Where black Sigatoka appears, or has been introduced, yellow Sigatoka disappears within about 3 years. Black Sigatoka has set the current agenda for fungicide application throughout the banana growing world.

The first symptoms of black Sigatoka appear on the lower (abaxial) leaf surface as a dark brown streak around l-2mm long. Lesions increase in size and subsequently develop into dark brown to black advanced streaks up to 5 to 10 mm long with an ill-defined border. Advanced streaks coalesce...