Q.I’m having a problem with my Japanese blueberry trees. Some are fine but the
two on the end appear to be drying out from the top down. Do you have any idea what’s causing this? The
soil is not dry and they all get the same amount of irrigation.
A.
The usual problem in damage or death to the top of a tree can be found on the
main trunk just below the damaged area. I am guessing something has damaged the
tree at that point.
The reason for the damage could be
several. Borers cause mechanical damage to the trunk and shut off the water
going to the top. Diseases in this same location can do exactly the same thing.
several. Borers cause mechanical damage to the trunk and shut off the water
going to the top. Diseases in this same location can do exactly the same thing.
Because Japanese blueberry is
relatively thin barked, sunburn from our intense sunlight can kill the trunk in
that location and shut off water to the top. Humans can cause damage to the
trunk and shut off its water supply as well.
relatively thin barked, sunburn from our intense sunlight can kill the trunk in
that location and shut off water to the top. Humans can cause damage to the
trunk and shut off its water supply as well.
 |
| Top of dead stem on readers Japanese blueberry |
I think we can rule out pathological
diseases in our climate. The two most likely culprits are mechanical damage to
the trunk by borers or the same type of damage caused by sunburn.
Inspect the trunk at the location
just above the healthy area of the canopy. Use your fingers and see if you can
pull away any loose bark. Borers tunnel just under the bark usually on the side
towards the most sunlight. This kills that part of the trunk and the bark peels
away easily.
just above the healthy area of the canopy. Use your fingers and see if you can
pull away any loose bark. Borers tunnel just under the bark usually on the side
towards the most sunlight. This kills that part of the trunk and the bark peels
away easily.
If you don’t see bark peeling from
the trunk at this location, look for discoloration of the trunk on this side
facing the sun. Sunburn to the trunk can happen in one hour of intense sunlight
during the midday or late afternoon.
the trunk at this location, look for discoloration of the trunk on this side
facing the sun. Sunburn to the trunk can happen in one hour of intense sunlight
during the midday or late afternoon.
If it is borers there is nothing you
can do to raise the dead area back to life but you can protect the tree from
extensive borer damage with an insecticide soil drench once a year.
can do to raise the dead area back to life but you can protect the tree from
extensive borer damage with an insecticide soil drench once a year.
In any case, you’ll be forced to
remove the dead top from the tree with a pruning shears or saw this winter. Once
you do this, it may open remaining branches for sunburn as well. Give them as
much protection as you can.
remove the dead top from the tree with a pruning shears or saw this winter. Once
you do this, it may open remaining branches for sunburn as well. Give them as
much protection as you can.
I would not do it now because the
sunlight is too intense and will probably cause even more damage to the lower,
healthier part of the tree.
sunlight is too intense and will probably cause even more damage to the lower,
healthier part of the tree.
Would you just cut off all the dead tops as well ?
You have to remove the dead tops. When you cut and remove the dead tops make your pruning cuts inside the canopy of the plant so that you do not leave it open for more sun damage to occur. The reason the plant had bores in them after the sun damage was because of exposed stems that received too much sun. By pruning deep inside the canopy you leave the shade remaining so that the plant gets less sun damage to the exposed branches.
Would you just cut off all the dead tops as you go ?