Question
I have 2 white paper birch trees and noticed a couple of days ago that an orange stain was showing on the trunk of one of the trees and seemed to be spreading. It seems to be running sap. The other tree is also developing orange spots and I also noticed small round holes in the trunk. They are not D holes. I am assuming some kind of boring insect. What can I do to save my trees ?

Answer
Sounds like it could be Bronze Birch Borer. The bronze birch borer attacks paper (canoe), European white (especially cutleaf variety), gray, yellow, and other birches, as well as poplar, cottonwood and willow. The larva bores in the trunk and larger limbs, often girdling them. Trees weakened by drought or injured are most susceptible to attack.Tree injury is caused by larval tunneling in the inner bark or cambium. The girdling of the trunk or branches interrupts sap flow downward to the roots and destroys the tree's cambium tissue. The interruption and subsequent accumulation of sap flow above larval tunnels often causes characteristic swollen bands or vein-like ridges in trunks and affected branches. The galleries range to approximately 1.5 meters (5 feet) in length and are packed with a dark brown sawdust-like frass.

Adults begin to emerge through "D" shaped holes in the bark in early to mid-June and may continue for five to six weeks. They feed on the foliage of alder, aspen, birch, willow or poplar for at least a week before beginning to lay eggs in bark crevices or beneath loose bark. Like other flatheaded borers, the bronze birch borer is attracted to the sunny side of trees for feeding and egg laying (oviposition). Areas of recent injury, mechanical or other, appear most attractive to the borer. Females lay up to 76 eggs, which hatch in two weeks. The larvae bore into the inner bark (phloem) and cambium to feed. Mature larvae construct oblong cells in the thick bark or wood in the fall and pupate the following spring. There is only one generation per year.

Since it sounds like the borer has entered the trunk spray the trunk with an insecticide called Merit. This will control the insect under the bark but depending on how much of the cambium layer has been killed the tree may still exhibit dieback of the foliage. The cambium layer is the living cells under the bark and if the layer is killed all the way around the trunk the tree may die.

Bayer Tree and Shrub Insect Control (imidacloprid): This product is labeled for both roundheaded and flatheaded borers. It contains the same active ingredient found in Merit and is systemic in the tree. Historically systemic insecticides have given poor control of borers. It appears that imidacloprid is better on flatheaded borers than roundheaded borers though even the results on flatheaded borers are inconsistent. Flatheaded borers are more likely to be controlled because they feed more in the vascular tissue than the roundheaded borers and are more likely to take up the insecticide. Examples of flatheaded borers include the bronze birch borer. This is applied to the soil round the tree and the roots will take up the insecticide killing the borer.


There are other borers that can attack Birch I would not take a chance and go ahead and treat with the Bayer product. It is applied to the soil and the roots will take it to the stem and branches. Here is a web link to this product. http://www.bayeradvanced.com/tree-shrub-care/products/12-month-tree-shrub-insect... Check with your local garden type store for this product.