African Sumac Attacked by Borers

Q. What should I do now with my 14-year-old, damaged African sumac? I think it had borers as you mentioned in a previous column, but the tree top is lush and green and showing no dieback of the limbs.

A. Many older trees damaged by borers show only subtle, outward signs of damage. Early borer damage is difficult to see. It isn’t until damage is extensive, usually from attacks every year, does it become obvious to the casual observer because of limb dieback.

This is a Purple Robe locust but it developed sunburn on the side facing the sun and this damaged area was followed up by an attack of borers. 

            I can see in the picture you sent that the borer damage to the trunk is healing. Encourage this type of healing with regular watering coupled with fertilizer applications twice a year. If it hasn’t been fertilized during the past 12 months, make an application when temperatures cool off a bit.

            The best time to see “hidden damage” in the spring done by borers is immediately after a good rain. Damage to trees due to borers is expressed through the wet trunk or limbs as a reddish, jellylike ooze. If not seen right away, this “jelly” dries in a day or two leaving reddish crystals behind.

Sap can sometimes be seen from trees attacked by boring insects. The best time to see this sap losing from the tree is immediately after rain.

            It looks like a limb broke and ripped the trunk, perhaps as it fell. This could have been because of previous borer problems that weakened the tree at this location. The central core of all trees is dead and surrounded by a cylinder of living tissue that can heal these types of wounds.

Sometimes trees can recover from an attack by boars if they are removed with a sharp knife or killed with a systemic insecticide.

            This living cylinder can be thick or thin depending on tree health. When trees are healthy and vigorous, this living cylinder repairs damage quickly by “rolling over” damaged areas as seen in your picture. Large areas can heal over in a couple seasons of growth if the tree is healthy.