Primarily on broccoli in the United States
This disorder is most commonly seen when broccoli heads reach maturity. Sepals of individual buds turn from green to yellow to brown. As the necrotic buds die, they often dry up and senesce. This opens an avenue for soft rotting bacteria (Pectobacterium spp. and Pseudomonas spp.) to enter the host and cause further damage.
Conditions for Disease Development
Brown bead is often seen when a period of high soil moisture is followed by a period of high temperatures and rapid plant growth, especially at the time of bud development. Widely varying relative humidities play a role in the expression of brown bead. Lack of boron may also be a contributing factor to this disorder.