Question
I have a much beloved crab in the middle of our small garden, and for the past four years it has had fire-blight.  I want to do everything I can to save it.

My neighbor has just cut down all three of their crabapples becasue they had the fireblight.

For the past two years, around the end of July and during August, when the fireblight appears, I have had a tree company cut off the affected branches, washing the pruners in bleach after each cut.

Last spring and this spring, I have had three sprayings against the virus.  The same tree company, which has done the spraying, has warned me that it might not help, and last year even after the spraying one big branch had to go, but I love the tree so much I want to do everything I can to save it, so I am continuing the spraying.

I have three questions.

1) Should I ask the person who cuts my grass to use a blower every couple of weeks to blow up the dead leaves that fall on the ground because the leaves might spread the virus?

2) Will cutting the suckers around the trunk help (because it will send the tree's strength to the existing branches) or hurt (because every open cut makes the tree more vulnerable to the virus)?

3) I have heard that too much water is bad for crabapples.  I water the lawn around the crab for 20 minutes twice a week in the early morning.  Should I water less?

In addition, if you know anything else that might help, I would be very grateful.

Thank you!  

-- Obessed with my lovely crab in Cambridge Mass.

Answer
Crabapples and other pome fruit trees vary in susceptibility to fire blight. It sounds like you have a highly susceptible variety.  Fireblight is a bacterial disease and once a tree is infected, it cannot be cured.  The purpose of bactericides is to prevent the disease from being spread to healthy areas of the tree.  Since the tree is infected, some of the pathogens' movement will be internal and cannot be stopped.  

I would periodically examine the tree and verify that there are no visible cankers present.  If you find cankers, they need to be removed as soon as possible.  Fire blight cankers are generally sunken and dark brown to black in color.  Especially in the spring but also early summer, the cankers exude strings of bacteria which can be blown, splashed or carried by insects to nearby trees or healthy areas of the tree.  This is how new damage is initiated. Secondly, the bacteria are growing in the canker and slowly invading the tree.  If they reach large branches or the main trunk, they can girdle the branch and cause everything above it to die.

It is not necessary to have your lawn person blow away the leaves.  For this disease, it is not spread in the leaves.  The leaves contain only dead dried up bacteria.  If the tree should develop any fungal leaf spot problems, then the leaves should be removed.

I would recommend removing the suckers around the trunk.  If you do not have an infection in the trunk, this would be a way that one could be introduced.  When removing the suckers, prune only during dry weather periods.  Start with clean pruning tools and be sure to dip between each and every cut in a disinfectant solution such as 10% bleach.  If you are expecting wet weather in the next few days, I would recommend to postpone pruning.

As for watering, if your soil is properly drained and you have had dry weather, than watering should actually be beneficial.  It is best to select an irrigation method that avoids wetting the underside (canopy) of the tree.  Sprinklers that spray the canopy will wet the cankers and the bacterial strands can be splashed to healthy plant parts.  A sprinkler that waters without spraying the canopy of the tree is desired.  For instance, tractor sprinklers (http://www.amazon.com/John-Deere-4010J-Traveling-Sprinkler/dp/B0001ANC7M) can cover a large area, but do not spray high into the air.  It is best to water diseased trees in mid-morning.

A few other fire blight tips.

Succulent tissue is most susceptible.  This means the new growth.  Do not apply excess nitrogen to the trees since it promotes succulence.  This will mean adjusting your lawn fertilizer around the tree to a lower level since it is high in nitrogen.  Do not over prune the tree.  This will also promote succulence.  Only prune what is necessary.

If you are removing a canker, be sure to cut at least 10-12 inches below the canker site into healthy wood.  If you prune close to the canker, you will not eliminate all of the bacteria.

Do not irrigate during bloom time.  This is when the twigs are most likely to become infected.  Since the bacteria can be water splashed, irrigation should be avoided until after blooming is complete.


Since you truly enjoy your crabapple I wish you luck in your continued plight.  Your tree may survive for many more years.  I might suggest that you consider installing a crabapple tree that is resistant to fire blight now so that it will have time to grow and enlarge.  Resistance does not imply immunity, but resistant trees generally do not die from the disease.  There are so many varieties of crabapple to choose from.  Here are a few lists to review which include both crabapples and other pome fruits:
http://www.umassgreeninfo.org/fact_sheets/plant_culture/apples.pdf
http://www.ext.colostate.edu/pubs/garden/02907.html

Good Luck!