Why is the Top of My Birch Tree Dead?

Posted by shane - December 15, 2014 - Insect Pests, Insects, Diseases & Other Problems - No Comments
All over Red Deer and other Alberta towns and cities, the big mature birch trees are dying.  Why?

There are a number of factors that contribute to the decline of a weeping or paper birch.  First, the majority of our soils in the Red Deer area are clay-based, alkaline grassland soils, which are not particularly well suited for birch trees that prefer moist, acidic forest soils.  So they can be expected to live an abbreviated existence by that fact alone.

Dead top due to bronze birch borer infestataion.

Dead top due to bronze birch borer infestataion.

Birches also prefer moist, well drained soils, and aren’t exceptionally tolerant to drought conditions.  Stressed trees are prone to insect attack by birch leafminer wasps, and bronze birch borer, both of which heavily infest Red Deer trees. Birch leafminer is very common.  If your birch leaves are brown and crispy by late June, and the leave look like skeletonized, that’s leafminer.  There are several species with up to many generations of attack per growing season.  Birch leafminer doesn’t kill the tree directly, but it does add stress to already troubled trees, opening it up to attack by the more serious boring insects.  Leafminer attack tends to stunt the growth of trees by limiting sugar production in the leaves through photosynthesis. The presence of bronze birch borer indicates that your tree is in decline and most likely won’t recover, unless you can catch it in the very early stages, which is tough to do.  The first sign of attack is yellow, sparse, or stunted growth in the upper part of the crown.  This leads to twig and branch dieback  (see picture).  Trees often decline for several years before dying, although if conditions are right, they can die quickly.  I’ve pruned trees that seemed okay in late summer, only to have them die over the winter.

 So what can we do about bronze birch borer?

Every spring, as soon as your birch tree “leafs-out”, inspect the canopy.  Look at the ends of the branches for deadwood.  I always take tip-dieback in the crown more seriously than dead branches within the crown.  Tip-dieback can be a sign of serious problems, such as root dysfuntion or boring insects.  If you see tip-dieback, chances are it is out of your reach and you will need to contact a professional arborist.  I’m not telling this to make you spend money. I’m telling you this because if you want to save your tree, now is the time and you will need someone who can: 1) access the tips, and 2) knows what and where to prune the branches once he gets there.  So if you remove the die-back early enough, the arborist may be able to remove the borer infestation as well.

Inspect the tree in summer.  If there are branches that have flagging leaves (yellow/orange leaves that are dying but not falling off the branch), that is an indication of borer attack.  Now is also the time to call the arborist for the same reasons mentioned above.

There are chemical controls for bronze birch borer, but there effectiveness is limited.  I believe they slow the insect down but the trees continues to slowly decline.

What can we do about birch leafminer?

Birch leafminer is becoming so common that almost every weeping birch I see in Red Deer is affected by mid- to late June.  Some trees look so bad I wonder how they survive.  There are a number of controls.  Some work and some do not.  Many people are finding live nematode treatments from local garden centres.  They are costly and the feedback I’ve continue to receive is that they don’t work.

Leafminer infested trees in Westpark neighbourhood, Red Deer. S.LePage photo 2014.

Leafminer infested trees in Westpark neighbourhood, Red Deer. S.LePage photo 2014.

There are two chemicals that I use that offer good control: TreeAzin (derived from neem kernel oil), and Orthene (a conventional systemic insecticide).  I will also mention the chemicals Cygon and Lagon (same thing, and dimethoate is the active ingredient).  Cygon and Lagon are banned for use in residential areas, because they were found to leach into groundwater to enter our streams and rivers.  They offered excellent control (almost 100%) and I haven’t found anything that offers as good of control since.  That said, the other two systemics I use are very good and offer 85+% control.

TreeAzin: as close to “organic” as you can get.  Very safe for the applicator, homeowners, kids, and pets.  Applied by trunk injection and taken up into the trunk and into the leaves within 48 hours.  It is a feeding suppressant and the leafminer larvae starves inside the leaves.  This is a safe and effective chemical that will be the dominant treatment we use for this insect in the coming years.

Orthene: a system chemical applied to the foliage by spraying.  Orthene works very well, but it is also a very toxic chemical for humans, pets, birds, fish, and pretty much everything.  I use it in areas where spray drift can either be controlled, or is not a factor.  If there is any chance the drift will contaminate a neighbouring property, or there is any evidence of children or pets, I will not spray this chemical.  Thanks to TreeAzin, Orthene use is becoming obsolete for use on birch.

Chemical controls are best administered as a preventative treatment in late May.  Some people like to wait until they see damage, but by that time a large portion of the tree can be affected. If your tree is normally infested each year by leafminer, there is an excellent chance that it will be infested next year too, as the larvae overwinter in the soil beneath the tree.  Preventative control works.  Systemic chemicals must be applied annually.

TreeAzin applied by trunk injection. S. LePage photo 2014.

TreeAzin applied by trunk injection. S. LePage photo 2014.

 If I remove my infested and declining tree, should I plant another birch?

Maybe.  That depends on how much you like birch.  When someone asks us to remove a sick birch, I normally recommend 4 or 5 different species to use as a substitute for the next planting.  I don’t plant very many birch trees anymore, but if I do, it is only because the homeowner insists on having birch and is prepared for the annual preventative maintenance of controlling the pests.  Leafminer species attack all species of birch, including river birch, dwarf birch, actic birch, and hybrids.

What are some suitable species to use instead of birch if I want a nice shade tree?

We like ‘Prairie Cascade’ weeping willow, Silver-leaf willow, ‘Silver Cloud’ maple, ‘Patmore’ elm, ‘Sienna Glen’ maple, bur oak, trembling aspen, and others, depending on the exposure and the site.

(c) 2014 Shane LePage, Wild Rose Garden & Tree Service Inc., Red Deer, AB