• Botrytis is the major disease of onions in cool climate areas.
• Light infections do not affect yields but heavy infections causing major yield reductions can occur.
• Hundreds of white specks are seen on the foliage.
• The disease then spreads very rapidly and tops of the entire crop may be killed.

• Botrytis is characterized by its conidiophores which present an appearance of grapebunch. The conidiophores are tall, erect and branches irregularly or dichotomously. They are dark and septate. The terminal cells swell to produce sporogenous ampullae. On each ampulla numerous conidia arise simultaneously on short denticles. The conidia are hyaline or tinted, aseptate and globose to ovoid.

• Bulb treatment with Captan /Thiram 0.25%
• Spraying of Maneb or Mancozeb or Chlorothalonil.
• Fungicides may be applied every 5 - 7 days for disease control.

Source:

Images: http://aces.nmsu.edu/pubs/_circulars/CR538/welcome.html, http://www.padil.gov.au/pests-and-diseases/pest/main/136568/1837
Microscopic images: http://www.padil.gov.au/pests-and-diseases/pest/main/136568/1843, http://www.plantmanagementnetwork.org/pub/php/diagnosticguide/2006/pears/