Agriculture Reference
In-Depth Information
Importance
Powdery mildew is a sporadic field problem that occurs in
all mango growing areas. It causes the most serious losses
when f flowering and growth f flushes occur during dry, cool
conditions. Mango cultivars vary considerably in their
susceptibility to powdery mildew.
Management
Screen germplasm and only use resistant types as parents
in areas where the disease is prevalent.
Spray with the recommended fungicides at the correct
rates and timing of application. Avoid sulphur sprays at
fl owering, because they may scorch fl owers and young
fruit when applied under warm and sunny conditions.
SCAB
Fig 12.34 Scab symptoms on leaf petioles and stems.
Cause
The fungus Denticularia mangiferae .
However, close examination shows them to be raised areas
in contrast to the non-raised lesions of anthracnose.
Fruit: the most distinctive symptoms are on fruit. Small,
black lesions form on newly set fruit and severely affected
fruit fall off. Lesions on young fruit are greyish brown
scabs with dark, irregular margins. These lesions enlarge as
the fruit increase in size, eventually imparting a cracked
and corky appearance to affected fruit.
Symptoms
Leaves: lesions usually begin on lower leaves and are
circular to angular and dark brown to black in colour.
Common symptoms observed are brown spots with haloes,
lesions on leaf margins, corky lesions and elongated dark
lesions along main veins. During rainy weather, numerous
small, brown lesions or shot holes may develop on young
leaves. Infected leaves often become distorted as they
mature, due to the effects of marginal or leaf-edge lesions.
Source of infection and spread
Disease development is favoured by many factors,
including frequent irrigation that encourages lush growth.
Stems: the most common symptom on stem tissue is the
occurrence of numerous slightly raised, oval to elliptical
lesions. In dry environments, these lesions appear black in
colour, and can easily be confused with anthracnose.
Fig 12.33 Scab symptoms on mango leaves showing the shot hole
symptoms (right).
Fig 12.35 Mango scab symptom on fruit. Inset: detail of the lesions.
Search WWH ::




Custom Search