Causal Agent: 

Fungus (Alternaria cucumerina)

Characteristic symptoms:
 
Brown necrotic lesions initially appear on older leaves near the crown.
 
Affected leaves initially have small yellow brown spots with light green or yellow halo which eventually expand to large brown necrotic areas.
 
Conditions for Disease Development:
 
The pathogen can survive for 1-2 years as mycelium in diseased plant debris.
   
Sources of primary inoculum are conidia produced by dormant mycelium in cucurbit fields with recent history of the disease and airborne conidia.
   
Conidia/spores produced on foliage are disseminated by wind, rain splashes, tools/implements and field workers.
   
Humid, rainy weather favours infection.
   
Disease severity increases with increased duration of leaf wetness (2-24hr) over a range of temperature (12-30°C).
   
Management and Control:
 
Use resistant varieties, if available.
   
Removal or deep plowing of plant debris after the cropping season can help reduce primary inoculum.
   
Avoid overhead irrigation or prolonged moisture to reduce disease severity.
   
Staking increases air movement and may help reduce infection in the field.
   
Crop rotation with non-cucurbit crops for at least 2 years can reduce levels of primary inoculum.
   
Regular application of protective fungicides such as copper-based fungicides (e.g. Cupravit®, Super BlueⓇ, Vitigran blueⓇ, FunguranⓇ, KocideⓇ, Hydroxide superⓇ), mancozeb (e.g. Attain M-80Ⓡ, Achem Mancozeb 80 WPⓇ, Micron 80 WOⓇ, VanzebⓇ) or propineb (e.g. AntracolⓇ) can delay the onset of the disease and slow its development.
   

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