posted 8 years ago
It's gonna be impossible to tell precisely which borer it is based on the bore hole. Could be roundheaded apple tree borer, dogwood borer or a few others. Some are beetles, some are moths, all are little bastards. The grubby larval stage of life is feasting on the cambium and sapwood in the tree. The crown rot may likely be from phytophthora and is usually caused by either planting too deep or piling mulch up against the base of a tree. (Those trees we all see in office parks and shopping malls and parks that have pretty little donuts of mulch around the base of the trees will eventually kill them. Old trees that came from seed that look like they have feet with the crown fully exposed is a good example of how the base of a tree should appear.) Looking in your photo it also appears that there are cankers on the tree, which are often caused by bacteria. There are a couple ways to approach the borers. One is clay based slurries you can apply to the trunk to repel egg laying females. Frequent applications of raw, unadulterated, cold-processed neem oil (diluted in water of course) can help disrupt the life cycle of the borer. Raw neem oil also has some amazing qualities for preventing diseases too. These methods work best to prevent such maladies from afflicting your trees. Your poor trees have sustained a lot and it is quite likely they will never recover. May I suggest planting new trees while also trying to nurse these along if you really want to save them. Quality fruit bearing trees take years to get established and it may be a good idea to have a backup plan planted now instead of trying to rescue these trees only to have them die in 3 or 5 years anyway. One thing you should be aware of is if you plant new trees in proximity to the sick ones, the injured trees already have a weak immune system and can harbor other diseases and result in high disease pressure on your new trees. And by proximity I mean a couple hundred yards. Regardless of what you choose to do, don't let organic matter pile up next to and be in contact with the base of a tree. If you did try to plant them extra deep, and the fruiting cultivar did indeed happen to sprout roots, the trunk will eventually rot. This may not have been what you were hoping to hear, but from the pictures your trees are in bad shape and may I suggest cutting your losses and starting with new trees from a reputable nursery. Hope this helps!
"Study books and observe nature; if they do not agree, throw away the books." ~ William A. Albrecht