Many broccoli varieties are intolerant of hot weather. High temperature affects the quality of broccoli heads by causing uneven development of buds. This results in heads being uneven and poorly shaped. Indents in heads from uneven growth form areas where water can remain for extended periods following rain, heavy dew and irrigation, thereby creating conditions favorable for infection by soft rot bacteria. The critical period during which heat causes uneven bud development in broccoli is about a 10-day period when the growing tip shifts from vegetative growth to flower bud initiation. This is before a tiny crown is visible in the center of the plant. Heat can also kill buds which further predisposes heads to head rot caused by soft rot bacteria, which is visible in the last image below. These photographs were taken on 26 November 2017.
