Ah, what a beautiful thing is the marriage of intelligent minds!
In early June, 2002 I received three questions in one week asking about cherry trees that were oozing sap. Sensing an incipient problem, I queried my Extension Service colleagues if they had had similar questions.
Some replied that they had seen the phenomena but were unsure of the cause. Gary Peiffer, my tree guru in DeKalb county, felt that the basic cause was stress. Randy Drinkard, in the Bartow county office, opined that the sap flow resulted from the extreme temperature swings that our area experienced in winter.
TEMPERATURE “The Atlanta/North Georgia area actually had some pretty warm winter temperatures earlier this year.” he said. “We had seventy degree readings in January and February for instance, followed by freezing or near-freezing temperatures soon thereafter.
My theory is that rapid winter temperature fluctuations often cause thin-barked plants, especially flowering cherries, to develop minute, barely visible cracks. The cracks partially reseal during cooler weather but then reopen and ‘bleed’ during summer when temperatures rise.
The Bibb county Extension agent, Aaron Lancaster, contributed an Internet link to a Texas A&M document that gave three causes of cherry “bleeding”: borers, mechanical injury or canker.
BORERS It is true that cherry borers can tunnel under the bark of a tree, causing sap to seep. In my experience, the sap that solidifies on the bark will have sawdust in it. When the hardened sap is dislodged a small hole will be visible in the bark, through which the liquid sap oozed originally.
INJURY One of the best reasons to mulch around a tree isn’t to conserve moisture. It’s to keep lawnmowers and string trimmers at bay. Cherry trees have thin bark. When it is damaged by machinery or by kids climbing it while wearing their soccer cleats, sap will seep until the tree can wall off the injury internally.
CANKER When tree bark displays a generalized soft ooziness, gardeners christen it a canker. The canker can be bacterial or fungal in origin. Bacterial cankers usually have more “liquidity” than fungal cankers.
In the weeks since June I have gotten a dozen more complaints about oozing cherry trees. Which of the four causes above might be the culprit?
I laid out my explorations to Dr. Jean Williams-Woodward, an Extension pathologist in Athens. Her opinion was that winter temperature fluctuations have been the culprit this year. Whether the sap oozed from broken but healthy bark or from a canker that infected the tree after winter injury the visible symptom is the same. Her prescription? Baby the tree this year and next, making sure it has water in summer. According to her, no spray will be of any help.
ACIDITY Jean passed on to me another cause of stress to cherry, peach and plum trees: low soil pH. Trees in the peach family are very sensitive to acid soil. Most soils in the Atlanta metro area tend to be acid so flowering cherries often struggle to overcome this environmental factor.
Jean suggests that you first have your soil pH tested by your local Extension office (404-897-6261). A quick method of raising soil pH in a limited area is to apply hydrated lime. This chemical is available at most garden centers. You’ll need one-half pound for every inch of tree trunk thickness.
Mix one pound at a time in five gallons of water and sprinkle it evenly under the drip zone of the tree. Use caution when handling or mixing the stuff – hydrated lime powder is extremely caustic. Afterwards, scatter garden lime over the spot, again at the rate of one-half pound per inch of trunk diameter. Water everything into the soil thoroughly. If the tree survives the next few years, have the soil tested again to make sure the pH is between 6.0 and 7.0.
Unlike the satisfying ending to a Sherlock Holmes mystery, “The Case of the Bleeding Cherries” didn’t point to a single culprit. However, the pleasure of working in tandem with dedicated and knowledgeable experts gave me enough enjoyment to bring this detective story to a close.