Grant: Pear fire blight | Way of life

If you've ever grown pears, you've probably noticed dead twigs, dead branches, and even entirely dead trees depending on the cultivar. In wet, disease-prone years, fire blight is usually to blame.

According to our publication on fire blight of ornamental pears by Shelia McBride and Dave Appel, fire blight causes vascular wilt of many varieties of pome trees (apples, pears, and ornamental pears) and other members of the rose family (Rosaceae). This is perhaps our most important fruit family, which also includes peaches, nectarines, plums, apricots, blackberries and strawberries. In vascular wilt, pathogens block the plant's water transport (vascular) system, causing leaves, stems and branches to wilt, weaken and die. Fire blight, one of the most destructive diseases of commercial apples and pears, is also a serious disease of popular ornamental Bradford pears used in many East Texas landscapes. Other common ornamental woody plants in Texas affected by fire blight are loquat, cottoneaster and pyracantha.

Symptoms: Infected flowers become water-soaked (translucent and wilted), shrivel and turn brown. The leaves gradually turn brown, develop black spots, curl and eventually shrivel. The twigs wilt from the tip down, turning black and curling into a “shepherd’s crook,” giving them a burnt appearance. Branches develop dark, sunken cankers that enlarge and girdle the branches. Eventually, the entire branch may die.

Causes and environmental factors: The bacterium Erwinia amylovora is responsible for fire blight. The pathogen overwinters in cankers, bud scars and branches; forms a silt that attracts insects, including bees, which then spread bacteria via nectarthodes (openings at the base of flowers); also spreads by rain, which splashes bacterial slime and causes new infections; and infects new, tender, succulent twigs and leaves.

Control: During winter dormancy, use sanitary pruning to remove infected wood. Cut off an infected branch 4 to 6 inches below the visible wound or canker. To prevent the spread of bacteria while pruning, disinfect the pruning tool before each cut, using a 10% bleach solution (one part bleach to nine parts water). To prevent rust, dry and oil your tools after using them.

Reduce excessive succulence by avoiding extreme fertilizing and watering. Resistant plant varieties. When possible, reduce new infections by spraying an antibiotic such as streptomycin sulfate (Fertilome® Fire Blight Spray) on flowers or shoots before the bacteria infects them. A copper sulfate fungicide (Bonide® Copper Fungicide) is also an option when applied multiple times while the flowers are open. (None of these options will eliminate all new or existing infections in the wood.) Refer to product labels for proper doses and usage.

Although fire blight can kill susceptible tender pear cultivars such as 'Barlett' (European types are particularly susceptible), it only temporarily spoils the appearance of 'Bradford' and other ornamental cultivars of Pryus calleryana, a more resistant species. Personally, I would not take the time or expense to spray pear cultivars and would rely on resistant cultivars, sanitation and proper cultivation.

For more information, visit the Texas A&M AgriLife Extension Service's Texas Plant Disease Diagnostic Lab website or follow them on Facebook at “Texas Plant Disease Diagnostic Lab.” You can also learn more about blight-resistant pears in the “Pears” publication on the Aggie Horticulture website under the Fruit and Nut Resources tab.

— Greg Grant is the Smith County Horticulturist and Texas A&M AgriLife Extension Service Master Gardener Coordinator. He is the author of Texas Fruit and Vegetarian Gardening, Texas Home Landscaping, Heirloom Gardening in the South, and The Rose Rustlers. You can read his blog “Greg's Ramblings” at arborgate.com, read his “In Greg's Garden” in every issue of Texas Gardener magazine (texasgardener.com), or follow him on Facebook at “Greg Grant Gardens.” More lawn and garden science information from the Texas A&M AgriLife Extension Service is available at aggieturf.tamu.edu and aggie-horticulture.tamu.edu.