Over the past few weeks, many homeowners have called our office or sent e-mails with attached photos of blackened leaves at the tips of stems and branches of their apple, pear and crabapple trees.
Everyone wants to know – what is making their fruit trees sick?
The culprit is the disease known as fire blight. Fire blight is caused by the bacteria Erwinia amylovora, which can be transmitted by bees, aphids and other insects, as well as by wind and rain.
Weather conditions conducive to its spread occurs when temperatures are 65 to 90 degrees combined with humid or rainy weather. Typically, this occurs during spring and into early summer.
Once the disease is established, it can be very difficult to control.
Fire blight infects blossoms, fruits, twigs and branches. The first symptom of this disease starts in the spring when the fruit tree flowers. The blossoms will appear water-soaked, wilted, shriveled and finally turn brown to black.
Once infected, branch tips wilt quickly, taking on the characteristic shape of a “shepherd’s crook.” After fire blight gains entry into the tree, the bacteria spreads internally through the stems and begins to work toward the trunk and down to the roots.
Infected leaves remain on the branches, giving the appearance that a fire went through the tree, thus why the disease is called fire blight.
Once infection has occurred, there are no curative sprays. The only treatment option is to cut out infected limbs to help minimize damage. To help prevent future infections, sprays of agricultural-grade streptomycin and tetracycline applied at early bloom have been the standard commercial control since the 1950s.
The best way to minimize the spread of fire blight is to purchase varieties of apple and pear trees that have some resistance to the disease.
Apple varieties more susceptible to fire blight include: Fuji, Gala, Jonathan, Lodi and Yellow Transparent. Varieties less susceptible include: Arkansas Black, Empire, Liberty, Pricilla & Red Delicious (source ATTRA’s Apples Organic Production Guide).
Pear varieties moderately resistant to fire blight include: Keiffer, Moonglow, Magness, Orient and Seckel (somewhat resistant).
Crabapples with moderate resistance to fire blight include: Adams, Donald, Wyman, Pink Princess, Robinson, Profusion and Velvet Pillar.
Sanitation practices such as pruning infected twigs and shoots help manage fire blight before growth starts in the spring. Apple and pear trees should be monitored removing symptomatic twigs and branches as seen.
Cuts should be made eight to 12 inches beyond the last evidence of the disease. Prevent the spread of the bacteria by hands or cutting tools by using a 10 percent bleach or Lysol solution to sterilize pruners and loppers between every cut.
A copper spray in the dormant or green tip stage and streptomycin sprays during bloom, are needed to manage fire blight on susceptible cultivars.
Copper sprays will help reduce the inoculum of the fire blight, but will not provide adequate control alone. Streptomycin sprays at first bloom protect only the open blossoms; consequently, additional applications are needed every three to five days during the bloom period.
For more information on how to control fire blight, visit https://www.ces.ncsu.edu/fletcher/programs/apple/plantpath/FBfact.html.