Fireblight

Fireblight is a bacterial disease affecting apples, pears, and some other members of Rosaceae. Pears are the most susceptible. Control is chiefly by pruning out affected areas, though streptomycin sprays are effective in those areas where the endemic bacteria is not yet resistant to them.

The bacteria is spread mainly by wind, and to a lesser extent by birds and insects.

The disease spreads during hot, wet weather. Blossoms and new growth are the most susceptible portions of the tree. Overpruning and overfertilization (especially with nitrogen) can lead to waterspouts and other midsummer growth that leave the tree more susceptible.

Fireblight is not present in Australia.