Sign of birch borer or not?

[allina]

Planted this Dakota Pinnacle birch about 4 years ago and last spring it started showing signs of the tree's leader drooping, newer lateral branches less upright and upper canopy becoming more sparse. It did seem to put on some growth in the leader this last year so did the leader just "outgrow" itself or is there something internally going on? The first attached picture was taken late October of 2016.

Being patient at the behest of my wife I thought I would see if the tree would properly leaf out and show signs of developing a more upright branch structure at the top of the tree. The second attached picture is of the tree as it appears as of late April 2017. The third attached picture is a close-up of the upper branches from early May 2017.

How much more patient should I be ? The past 2 years I've used a systemic insecticide, imidacloprid (Optrol ®) as prophylaxis against bronze birch borer of which the Dakota Pinnacle is supposedly pretty resistant to already. Thanks in advance for any advice you could provide.

 

[JD3000]

Be more patient. Imidacloprid should take care of Agrilus borers but make sure you pull back the mulch to expose the mineral soil before applying the product. This insecticide can bond to organic matter before reaching the root system. Follow with a light watering and put your mulch back in place while keeping the root flair exposed.

Interior leaf yellowing can be due to nitrogen deficiency as well as a water defecit. A little slow release N fert may be in order but summer watering is more important in all likelyhood. White birches tend to be native at higher latitudes and can resent a hot dry summers and springs.

 

[DSMc]

......Interior leaf yellowing can be due to nitrogen deficiency as well as a water defecit.....

Or it could be because it was October. Judging by the lush green lawn and the dark green of everything in the spring picture, lack of nitrogen and water do not jump to my mind. How much weed and feed and water is the lawn getting?

If the Optrol was applied according to label it should eliminate the borer threat. The most common problem that we see is stress from planting trees too deep and bad root systems from nursery mismanagement.

 

[JD3000]

Was it October? Shoot...

Or excess mulch which we can't see from the pic.

 

[JD3000]

Also too many trees planted close together

 

[allina]

original poster here. Thanks for the responses.

The Dakota Pinnacle birch was not planted too deep (clay soil base so I actually planted the root flare a bit higher than ground level) nor was it "overmulched" in the picture supplied, If anything the mulch was bit thin but seeing that the first picture was in October with cooler weather I hadn't yet applied its winter "coat" of mulch. I contract with a lawn service company who applies the fertilizer and the lawn looks good in background given the wet spring we've had.

Can a soft wooded tree such as a birch which is planted not in its native surroundings and is subjected to routine suburban lawn maintenance possibly have the leader grow "too fast" not harden off in order to grow in its natural upright form?

 

[ghostice]

One of the things I've been told about birch is that they do not seem to like having their root systems exposed to hot summer sun - as I write this I am looking at a white birch in neighbour's yard that is about 1/3 the size of the rest of our neighbourhood's birch trees after 25 -30 yrs. It faces full sun in south backyard all day long. Mulch is good, but also if your climate tends to get hot and dry in summer, I've been told that keeping the roots cooler/ shadier by maybe using small shrub plantings out from the base of the tree is probably not a bad idea. Also if you have a lawn fert company using grass fert a lot of times it's just N and little or no P or K. More balanced fert might be good if it's not, with micronutrients. Watering with a root feeder from 2 feet down, upwards - gets lots of air into the soil. Also check your trees for multiple layers of landscape fabric around the root zone - around here they go wild with the stuff - I've pulled four layers off from around some struggling trees and a year later - magic - green again!