Janna Beckerman, Department of Botany and Plant Pathology, Purdue University
Fire blight has become a serious problem this year on ornamental pears and crabapples, and even apples and pears in commercial orchards. Erwinia amylovora is the name of the bacterium that causes this disease. After having overwintered on cankers that formed last year (Fig.1), it has been spreading like…wildfire throughout Indiana. This pathogen is primarily infects flowers, and is spread by insects, wind and rain. It also gets into small lesions caused by hail. The bacteria begins infecting flowers, and then spreads to the entire shoot, causing the characteristic shepherd’s crook (Fig.2). On pear, the damage looks black, and scorched, giving it the name ‘fire blight’. Within the year (on young trees) or several years (on older ones, or stressed trees) it can get into the rootstock, killing the tree (Fig.3).
Pruning out fire blight infected branches is essential to managing the disease before more than 30% of the upper portion of the tree is infected. Pruning must be done correctly and at the right time to be effective. Ideally, late winter is the best time to prune out fire blight cankers before new growth begins. For trees with minimal infection, make sure the terminal bud has set. This has already happened in Southern Indiana, but patience may be necessary for another week or two in Northern Indiana. When pruning, be sure to: