Although resistance to insecticides may occur in some cases, failure of contact sprays is more often the result of not timing the applications to coincide with crawler activity. Even when sprays are timed for optimum effect, complete control may not be achieved by single applications if crawler activity is spread over an extended period of time, or if populations are heavy and crawlers are under old scale shells. Thorough spray coverage is essential for good control. The leaves of plants affected by fireblight appear to have been scorched black. Flowering shoots die, and cankers, cracks and dry spots may appear on the base of twigs.
Stems affected with fireblight take on a shepherd s crook appearance.
Fireblight targets members of the Rosaceae family, and plants are most susceptible during flowering. Warm, wet conditions also contribute to the spread of the disease. For now, all that can be done for control is to prune back infected branches and twigs at least six inches below the damaged area. Pruning tools should be disinfected between cuts. In future years, trees should be sprayed with fixed copper when trees are just breaking dormancy.