A couple of weeks ago I sat and admired my beautiful dwarf Japanese maple. The burgundy leaves had filled in and it looked so nice in the container next to the deck. It was a pat yourself on the back moment! Then the next day when I went over to gloat again I noticed the leaves were covered with brown spots. Ok, it wasn’t exactly the next day and the brown areas aren’t exactly spots either but still it was one sad looking plant.
What I discovered is a non infectious condition called leaf scorch. It is often mistaken for for a disease but it isn’t caused by the usual suspects – fungus, bacteria or virus. Leaf scorch is a warning sign that something is negatively impacting the plant. Water is being lost from the leaves quicker than the veins can transport it. This is most often caused by an unfavorable environment, and the symptoms are typically light brown to tan areas found between leaf veins or the leaf margins. The color can also be yellow or chlorotic. Even though it sounds simply like type of “sunburn”, leaf scorch can be a little more complicated especially in the Piedmont.
There are many conditions that can lead to leaf scorch including dry hot winds, temperatures at/above 90 degrees, drought conditions and low humidity or even drying winds when the ground is frozen. There are some less obvious conditions that may impact Japanese Maples that should be investigated if you are unable to pinpoint the cause at this point. One of these is soil condition such as poor heavy soils – which is so common in the south. If you are planting the tree in the ground, please get your soil tested!
A small specimen grown in a pot will primarily be impacted by weather conditions. So far spring in the Durham area has been wild. Days of cool and rainy weather followed by wind and 90 degrees temps are perfect conditions for leaf scorch. Trees in very sunny and windy locations are even more susceptible.
So what to do…to begin with make sure you have chosen not only the right Japanese Maple but also the correct container to grow it in. Try keep the tree shaded from afternoon sun and protected from the wind. Test your potting soil for mineral imbalance and check for insects. Neither of these are the cause of leaf scorch but healthy plants are warriors! Then make sure you water thoroughly each time versus a little now and then. Make sure to cover the soil with a fine mulch. The reality is the damaged leaves will not get better and there will probably be more of them but if you take precautions this isn’t a death sentence for Japanese maples. Don’t let visitors get too close and no one will notice. Well, except maybe me but I won’t say anything!
http://extension.missouri.edu/p/G6881
https://www.pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/430/430-023/430-023_pdf.pdf