Asian pears (Pyrus pyrifolia and also p. ussuriensis) are fast trees which produce across crisp pears. They are susceptible to the majority of the diseases suffered by the European species of this pear genus Pyrus. They especially suffer from the fungal diseases pear scab, powdery mildew and sooty blotch. Asian pears may be grown in U.S. Department of Agriculture plant hardiness zones 5 through 9.
Fungicides for Pear Scab
Velvety, dark olive to dark spots of pear scab develop on the leaves, stems and pears. These spots are fungal spores and may cause scabs on the surface of this pears, causing them to become misshapen. The fungal spores spend the winter on dead leaves and are spread by spring rains. The California Integrated Pest Management says the most effective fungicide is spraying lime sulfur on diseased twigs when the trees are dormant. The best fungicides implemented when the trees demonstrate green hints through the spring growing season, ranked by effectiveness, are those containing the active ingredients fenamirol; triflumizole; diefenoconazole and cyprodinil; teubuconazole and trifloxystrobini; trifloxystrobin; pyraclostrobin and boscalid; cyprodinil; kresoxim methyl; pyrmimethanil; thiophanate methyl; mancozeb; dondine and lime sulfur. Check with your county extension agent to find out the constraints and specific conditions which apply when using those fungicides. IPM warns that if one fungicide is used year after year, the pear scab fungi may develop a resistance to it.
Fungicides for Powdery Mildew
The California Department of Natural Resources recommends spraying trees with wettable sulfur or calcium polysulfide, liquid lime sulfur. Spray when you see a light green shade in the swelling buds and again when the buds turn pink and are going to start. Repeat every 10 days until the spring rains stop.
Fungicides for Sooty Blotch
Sooty blotch (Gloeodes pomigena) causes black, sooty smudges over the surfaces of pears. Sooty blotch usually infects pears during intervals of early spring rain and continues into the summer. Prolonged cloudy weather and frequent rain showers make it more difficult. Appropriate fungicides comprise Thiophane methyl employed in combination with ferbam or mancozeb.
Fungicides to deal with Fire Blight
Fungicides aren’t restricted to combating fungal diseases. IPM recommends spraying pear trees with a 5 percent solution of Bordeaux mixture several times since flowers open to combat fire blight (Erwinia amylovora), a bacterial disease that causes oozing cankers on the bark of trees that are crocheted. Fire blight spreads in moist or humid weather especially with daytime temperatures over 75 degrees Fahrenheit. For your own Bordeaux mixture to be effective, you want to spray when the blossoms are open along with the average of the daytime high and nighttime low temperature is at least 60 degrees F. Spray blooms when they start in the spring and then apply every four to five days until late blossom is complete. The Bordeaux mixture is a combination of copper sulfate and lime.