By: Anthony Arnoldi - Board Certified Master Arborist WI-0102B
Wood-boring insects are at the top of the list of concerns arborists have for the trees they care for. They cause damage that cannot be ignored. Their damage is not just cosmetic, but significant, permanent and potentially lethal. Last year’s heat and drought has set up a situation where that concern is much more elevated.
Generally, borers are not able to attack just any tree they fly to. They need a tree that has been weakened or compromised in some way. They need a tree whose defenses are diminished and cannot fight back as well. (There are some exceptions to this, such as Emerald Ash Borer, that can attack perfectly healthy trees). Predisposing events that can put a tree at risk include root damage (like trenching, grading, soil compaction), storm damage, improper pruning, flooding, wounding (such as heavy equipment hitting the trunk), insect damage (defoliation, scale, etc.), and the list goes on. The extended heat and drought has been severe, and many trees have been stressed enough to have their defenses significantly compromised.
The Borers are waiting for spring, too. Their numbers are expected to be very high because more larvae have been able to complete their life cycle feeding on trees that were not able to defend themselves well last year. They have transformed into adults and will emerge from the trees looking for susceptible trees to lay their eggs on. And they will find such trees everywhere.
One group of borers has already been on the rise: bark beetles. These insects bore into the bark and in the first few rings of wood, destroying patches of trunk or limbs as they feed. One group of bark beetles in particular, Ips, is a big pest of pines (especially Red and Scots pines). It recently has attacked many more Austrian and White pines as well. As stresses have continued, it has even attacked Spruces much more heavily, and arborvitaes too. This is unusual and a harbinger for what is yet to come.
Oaks are expected to have much more difficulty with 2-lined chestnut borer. Oaks and other slow-growing trees don’t handle drought as well as some others and will need to be monitored for signs of infestations.
White-barked birches usually need help keeping Bronze Birch Borer from entering their trunks, but now that help will be imperative.
All trees have potential borer enemies, but many borers are problems only after trees are stressed greatly. We will be seeing much more from all borers, much like what happened after the heat and drought of 1988. This drought however was worse, in that the soils were much drier at the beginning of 2012 than they were at the beginning of 1988.
What can be done? Watering when dry this year will be paramount. Conserving moisture with mulch or compost will help. Increasing tree health and the ability to defend can be done with these procedures, as well as through fertilization, root biostimulants, mycorrhizae, and compost tea applications. Many borers have treatment programs that can defend key, susceptible trees well. These programs should be in place in many situations. Call your Wachtel Certified Arborist for help in determining what trees may be at risk and the best measures to protect them. This should be part of our efforts to weather the drought impact.