Fire Blight Fright~June 14, 2014

By June 15, 2014 Farm News

fire blight leaf 0614This leaf is not what we want to see on our apple trees.  Or our pear trees or crabapples, for that matter. As the seasons of the farm roll through, we find ourselves in the season of fire blight, which begins during bloom time and goes through June. Fire blight is a fast moving, destructive bacteria that will leave trees with cankered branches that must be cut out with the hopes of saving the remainder of the tree.

Steve says that he has fought with fire blight most of his life.  He remembers cutting out branches of pear trees when he was a kid on his family’s orchard in Grand Junction. Fire blight looks like a fire has singed branches and leaves throughout the orchard.  I can look out the window at our trees right now and see branches that are brown, withered and dying. The infections we see in the trees now actually began during bloom.  Fire blight is sort of like human Staph infection.  The bacteria can hang out on the bark of the tree or on your skin and are harmless.  But give them an entry point such as the nectaries of the flower or a skin wound and the results can be deadly.  Once the bacteria are inside the tree, there is nothing that can be done since it is darn hard to get a tree to take any internal medicine.  Try telling a tree to take two aspirin and call in the morning?  At least with Staph, people can take antibiotics.

The severity of a fire blight infection is influenced by moisture (dew or rain) and warmth during bloom.  When a blossom opens up and is fresh, a wetting event such as rain or dew can move the bacteria down into the floral nectaries, one of the few places they can gain access to the inside of the tree.  Then, if the temperatures are warm, the bacteria can multiply and reach a critical level where they move into the sap of the tree.  If there are warm temperatures or no moisture or moisture and cool temperatures, there is no problem.  But, when the combination hits, trouble looms.  During bloom, Steve watches for these wetting events and monitors temperatures, checking for possible infection periods.  It is a beautiful time of year, but stressful due to frost and these possible infections.

fire blight pruned trees 0614Above: Jonathon trees with the branches cut out to eliminate fire blight

Conventional growers can use antibiotics on their trees right at the time of infection to kill the bacteria and keep them from entering the sap. Organic growers are not able to use antibiotics as these materials are no longer approved by the National Organic Standards Board. To prevent infections, we attempt to keep the overall amount of bacteria in the orchard low by spraying other materials like copper and lime sulfur.  Then we apply a preventative yeast spray which can populate the nectaries.  The yeast will fill the niche of the nectaries where the bacteria likes to be and keeps the bacteria out. One variable in using the yeast for fire blight control is when we spray lime sulphur (a thinning spray), it can kill the yeast, so the sequence of applications is important. Another difficulty in managing fire blight is the time of year when infections occur. Steve is generally up to his eyeballs in planting, getting water in for irrigating, fertilizing and applying other sprays.  Spring is just plain busy on the farm and fire blight becomes another crisis to manage.

The hardest thing with blight is that it can kill the tree.  Many other things in the orchard hurt the crop, but leave the tree there for another year.  Not so with blight.  Orchardists and researchers have spent entire careers trying to eliminate or control fire blight, yet after all that research, once it is in the tree there is not much that can be done.  Steve likes to say that fire blight is akin to Civil War battlefield medicine. If a soldier gets shot in the foot, he’ll have to have his leg amputated at the knee or hip to save himself. Subtley is not an issue.  Fire blight is the same.  Once we see an infection in a tree, it’s already too late.  We have to “amputate” the limb 2-3 feet below where the infected branches are since the bacteria move ahead of the visible symptoms.

Some apple varieties are less susceptible to blight than others.  Unfortunately, many of the varieties you all love to eat are susceptible – Gala, Honeycrisp, Jonagold, Fuji, Esopus Spitzenberg… We have a block of Jonathon trees right now that are twenty-one years old that are dessimated due to fire blight.  Our crew is in the process of cutting out years and years of growth in these trees to save them. After each cut they have to disinfect the saws and shears so they don’t accidentally spread the bacteria with the tools.  It is pretty depressing to have an old block of trees where years of watering, pruning, fertilizing and picking have gone into them, only to have two-thirds of the tree cut out due to fire blight.  And even then, not being sure whether that will be enough.

fire blight branch 0614

Leaves on the right infected with fire blight

Some years of the blight are worse than others, this year is worse.  Steve didn’t see an obvious infection period at bloom and thought we were safe.  Then a few weeks ago he started seeing leaves curl up and got a sinking feeling.  As I was out in the orchard taking photos of the trees with our daughter the other day and talking about fire blight, she looked at me and said, “Mom, I’m going inside. Seeing all these sick trees makes me sad”.

Agreed. So in parting, here is our dog, who was happily tromping about the fire blighted trees, looking for someone to play with. Thank goodness for dogs.

Patches 0614

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