Insect damage, fungal infections, fire blight or stony pit virus can cause black leaves on pear trees. Frost damage, spider mite or pear psylla infestations, blossom blast, pear scab or sooty mold cause leaves with black tips.
Most often, leaves on pear trees turn black due to fire blight, a highly contagious bacterial infection. The culprit is the bacterium Erwinia amylovora. This disease not only attacks pear trees, but it endangers apple and crabapple trees as well.
Fire blight is identified early on by spots on the trees with bark that oozes a light tan material. This ooze leads to streaked bark. If left untended, the bacteria first infects open flowers and young fruit, which turn black. Eventually the leaves turn black and die as well.
Fire blight grows best during rainy weather with temperatures between 75 and 85 degrees Fahrenheit and attacks the growing wood first. In order to prevent fire blight, a gardener needs to avoid over-fertilizing or over-pruning the tree. These two actions promote growth, which creates the ideal home for the bacteria. A gardener also needs to cease watering the tree as it blossoms. If fire blight occurs, the infected growth needs to be pruned away and new blossoms sprayed.