What Is Burning Up My Pear Trees?
Does it look like someone tried to set your pear or apple tree on fire? You may be experiencing Fire blight, which is caused by Erwinia amylovora. Fire blight is a bacterial disease of apples and pears. The blossoms, fruit, twigs, branches and sometimes entire tree can die. The wilting starts at the branch tips giving the affected parts the look of a shepherd’s crook. The bacteria starts in the blossoms or in other openings or wounds in the tree and then moves down into it.
Spring weather promotes bacteria that has over-wintered in cankers in the trunk to spread up and out, carried by wind, rain and insects to new blossoms and shoots. We’ve recently had temperatures between 65-90F, with rainy / moist weather – just the way the fire blight bacteria likes it.
This infection takes hold in any wound or natural opening in the host plant and continues through the growing season. Each infection may result in new canker all its own, waiting for next season’s perfect conditions to set up house all over again.
So what’s a pear tree owner to do? Controlling this disease is tough, but you can reduce the severity of the blight.
First of all, choose resistant varieties (no immunity, just a bit of tougher fighting power). Some resistant apple trees for NC are the Golden Delicious, Lodi, Stayman, and Red Delicious. For pears, skip the Bartlett, Bosc and Clapp’s Favorite and go with Kieffer, Orient, Stark’s Delicious. Event the Magness and Moonglow are somewhat resistant.
Secondly, cut out the infection. All the cankers and blighted twigs need to be removed down 4-6 inches – up to 12 inches into the non-infected part of the stem. Remember, this is a bacteria. It hitchhikes on your cutting tools, your hands, etc… so practice disinfecting with 1:10 chlorine bleach solution or benzalkonium chloride (Lysol) between cuts. Don’t put the cut pieces in the compost pile. Burn them.
Thirdly, deal with the piercing, sucking insects like aphids with appropriate pest management methods. Watch during the flowering season. The bacteria can catch a ride on bees during pollination. We like the bees and need the pollination so during this stage use streptomycin products instead of insecticides that will kill the pollinators. A copper spray applied at the dormant/green-tip stage and streptomycin applied at the bloom stage can help manage the blight. Agricultural streptomycin (Agrimycin, Agri-Strep, for example) sprays at 1 tsp/gallon applied every 5 days when the petals start to open until they drop, then 2-3 sprays after petal drop every 7-10 days will help reduce the blight. However, streptomycin shouldn’t be applied within 50 days of harvesting apples, or within 30 days of harvesting pears.
In addition, watch the new growth. The bacteria like sweet, juicy, tender growth. Don’t go overboard with the fertilizer to make your plants shoot up too fast. Control the growth while maintaining the plant’s vigor and health. Slow and steady wins the race when we have weather conditions that promote this bacteria outbreak.
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The use of brand names and any mention of commercial products does not imply endorsement by N.C. Cooperative Extension nor discrimination against similar products not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label.
Minda Daughtry is Horticulture Agent for North Carolina Cooperative Extension in Lee County.