Over the past two weeks, we have had a handful of customers come to us with Purple Leaf Sand Cherries that showed symptoms of fire blight, a sneaky bacterial infection that causes the leaves and branches to curl and die. Although this disease can affect many plants, the Purple Leaf Sand Cherry (prunus family) is especially susceptible. Luckily, fire blight is not very common and is often mistaken for leaf scorch, which can be treated quite easily. So how can you tell if your sick tree has fire blight or leaf scorch? Here are some signs to help you identify the difference between the two.
- plant grew healthy in early spring
- leaf edges start to to turn tan/brown and become crispy and dry
- tissues between veins begin to turn tan/brown, making the leaf look as if it has been ‘scorched’
- eventually, the entire leaf became brown, except a small spot of green around the middle vein
- this appears most severely in the upper branches
If you have a tree that shows these symptoms, especially one that is newly planted, the culprit is most likely leaf scorch. Leaf scorch is usually caused by extreme heat and wind, under-watering or sometimes a combination of both. In hot or windy weather, water evaporates rapidly from leaves. Sometimes roots cannot absorb water fast enough to account for the loss of moisture, and the leaves begin to turn brown and wither. This usually occurs in dry soils, but it can also occur in moist soil if the weather is warm enough (~ 37º C). Newly planted trees or ones with small, shallow root systems are most susceptible to leaf scorch.
What to do?
To prevent further scorch, you should give your plant a deep watering during hot, dry periods. The idea is to water the plant slowly to allow the water to flow deep down into the root systems. Short, frequent watering periods only promote shallow roots and can make a tree more susceptible to drought damage.
How much water?
A general rule of thumb is to give a tree 10 gallons of water per every inch of trunk diameter (measure the trunk around knee-height). You can use a soaker hose and coil it several times around the tree to its drip line, or you can manually water with a hose. If you choose to manually water, we recommend using a hose end with a soft spray. It will take approximately 5 minutes to get 10 gallons of water, at medium pressure.
- your tree has a 2″ diameter
- this tree requires 20 gallons of water
- at a medium pressure it takes about 5 minutes to achieve 10 gallons of water
- a deep watering of this tree would only take 10 minutes
- plant grew healthy in early spring
- blossoms and leaves suddenly wilt
- leaves and twigs turn black as if scorched by fire
- affected leaves curl and hang downward
- tips of affected branches are where damage is most severe
- tips often hang down to form a “shepherd’s hook”
- bark at base of twig becomes water-soaked and then begins to darken and become sunken (canker)
- in warm and moist spring weather a brown, oozing, sap-like substance will appear on branch
As an example:
By giving your plant a deep watering, you can usually stop leaf scorch in its tracks. If the plant is newly planted and doesn’t seem to improve, give it some transplant fertilizer and provide a shade covering until the plant is established. If you continually find that your plant is getting leaf scorch, you may want to consider moving it to another location where it doesn’t receive the hot afternoon sun. In our experience, things like Japanese Maples are one of trees that are most sensitive and susceptible to leaf scorch.
Fire blight is actually a bacteria that overwinters on the cankers of various trees. In early spring the sap-like ooze releases to attract bees and other insects, which then carry bacteria-laden nectar to healthy blossoms. In warm humid weather, the bacteria quickly spreads throughout the tissue of the tree.
Here is a sample of a Purple Leaf Sand Cherry with fire blight. Notice the shepherd’s hook starting at the tip, and how water-soaked the leaves and branch look.
Controlling Fire Blight
During spring and summer, prune all infected branches 6-12″ below any signs of discoloration or sap. Make sure you throw these branches out and do not let any infected leaves compost back into the soil. Disinfect your pruning shears in between each cut to prevent spreading the bacteria (you can use a 50/50 solution of rubbing alcohol and water to disinfect). Keep the plant watered during hot spells, as the blight may have the plant under enough stress already. When the leaves have fallen off in spring, check for any more sunken cankers and do another pruning. We also recommend spraying your plant with a a copper sulfate-based fungicide to help prevent infection.
If you have a sick plant do not fear! The staff here at Rice Road are experienced with different arboreal issues and are more than happy to assist you with both the diagnosis and treatment of your plant. If you are noticing symptoms but are still unsure of the cause, cut off a small section of the affected area and bring it in for us to have a look (you may also bring in a picture, but we find that a sample is much more helpful). We are committed to helping you find the issue and to help you “nip it in the bud!”