Introduction to Apple Scab and Fireblight

My original plan for orchyard maintenance involved being passively organic by simply not doing anything beyond occasionally pruning. I expected a certain amount of fruit loss due to birds and insects eating the fruit and some drop in tree productivity due to insects eating the leaves and, since the fruit was destined for my own use, the prospect of having the occasional fungal spot on the fruit was also not a big deal. This worked well for me for the first growing season and as I went into the second season I was confident in the future of my passive approach.

The second season began with a spring which was relatively warm with frequent rains and heavy fogs on cool mornings. The young trees seemed to do well, and an old flowering crabapple by the road bloomed spectacularly. All was fine for a few more weeks, but as the season progressed I started to notice dark splotches on the leaves of the crabapple and the Golden Delicious. There were some on other trees as well, but not nearly to the same extent. I also noticed that many of the crabapples planted in the medians at parking lots around Indianapolis also showed these splotches, and I figured that it must have had something to do with the combination of cool rain and hot sun “burning” the leaves. Since it was so widespread it didn’t bother me and I figured if it was something serious than I wouldn’t see so many trees in a similar state around the city. A couple of weeks later, however, I noticed some of the tips of young branches looking dark and dried out, and in short order both the Golden Delicious and the crabapple were starting to look more brown and black than green. By mid June the young growth on both trees was severely affected, and the older growth was not doing very well. By mid July, both had papery dry leaves on most branches, but a couple of branches at the base of both trees had seemed to recover and were putting out new growth.

The next spring the crabapple only managed to push out one withered blossom, and neither it nor the Golden Delicious were able to push out any leaves. Hoping that warmer weather would help, I checked the swollen buds weekly and managed to convince myself that they were only a day or two away from opening each time. When several particularly warm and humid days sent the rest of the trees into a visible growth spurt and these two didn’t respond in the slightest, I gave up and cut them down.

In hindsight it became clear that these two trees had a contracted a combination of apple scab and fireblight which ended up weakening the tree to the point that it couldn’t respond to the need to put out new growth the following spring. When I realized that I could have done something about the apple scab, I hung my passive organic viewpoint up and opted to use a spray program with the fungicide Captan, which has helped me avoid similar outbreaks of scab in subsequent years. Although I have subsequently learned that it is possible to monitor weather conditions and strategically spray the trees with antibiotics to lessen the severity of fireblight, I am more comfortable keeping a close eye out for the tell-tale dark leaves and shepherd’s crook tip of new growth and vigorously cutting out the infected shoots than I am with spraying antibiotics.

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