Black pear tree
Pears are highly susceptible to a bacterial infection that blackens them from their leaves to roots. Called fire blight, it typically attacks in spring. With the spring warmth, it multiplies rapidly and you’ll see a liquid oozing from tree tissues. Insects carry this ooze to blossoms and infect them in turn. Blackening at other times signals an insect infestation.
The key to controlling fire blight is sanitation. Fixing pear tree problems with fire blight requires that you remove all old fruit and fallen foliage from the orchard. Prune back wounded or cankered branches – at least 8 inches below the problem area – and burn or dispose of them during winter. If you are just installing pear trees, look for cultivars with some resistance to this disease.
Repeatedly spraying your pear with organic Bordeaux mixture after its blossoms open reduces its risk of new infection. To make the mixture, dissolve 3 1/3 tablespoons of powdered copper sulfate and 5/8 cup of dried lime in 1 gallon of water. Many garden supply stores carry the ingredients. Apply the solution when the average daily temperature has reached 60 degrees Fahrenheit and rain or high humidity is likely. Treat the trees every four to five days until it finishes flowering. Always wear protective clothing, eyewear and gloves when handling any chemicals.
Another reason for the blackening is pear psyllas (Cacopsica pyricolla). These insects lay eggs in late winter on developing leaf and flower buds. Their nymphs feed on sap, injecting the trees with the pathogen responsible for pear decline disease and excreting copious amounts of sticky waste called honeydew. Sooty mold fungi landing on this honeydew germinate into grayish-black mats. Heavy sooty mold may compromise photosynthesis. Remove sooty mold by smothering the psylla insects with organic dormant horticultural oil. Mix a solution of 7 1/2 tablespoons of oil concentrate per 1 gallon of water. During the tree's winter dormancy, apply the oil with a pressurized sprayer at a temperature below 90 degrees Fahrenheit, watering the tree well before treating it. After saturating the infested leaves and branches, wait four hours before allowing children or pets near the tree. If necessary, repeat after one month. Without the honeydew-producing insects, the sooty mold starves and withers away.
Hope this helps!