Exceptionally wet spring weather exacerbates susceptibility of crabapple trees to a
dangerous fungus known as Apple Scab.
A recurring call that I repeatedly receive every year around June or July is that a property
owner’s crabapple tree is losing its leaves and appears to be dying — followed by an
appeal for help saving the crabapple tree.
Knowing the time of year that | receive such calls sometimes helps in diagnosing the
I respond with questions about the symptoms they should notice on the leaves, which
helps confirm my initial assessment of the problem.
I try to provide the best answer possible over the phone but it is important not to make
false assumptions without examining the tree in person.
The initial assessment is preliminary and cannot replace actually being on-site to
perform detailed diagnostics.
Apple scab is a fungus which annually occurs on older flowering crabapple trees and
worsens during wetter spring seasons.
Apple scab is a fungal disease that a lot of apple orchards are familiar with.
Typical symptoms include yellow leaves with circular brown-to-black spots followed
by leaves falling to the ground, beginning in early summer.
During years that begin with exceptionally wet spring weather, crabapple trees can
become totally defoliated by the end of June.
Apple scab should be considered a serious problem with the tree, because not only is
it unsightly looking, but the loss of leaves results in a serious debilitation of the tree to
capture energy to sustain itself.
Repeated defoliations year after year will cause the tree to decline over time.
The first and best solution is to replace the tree with a more scab-resistant variety.
Although some crabapple species are more resistant, that does not mean they are totally
resistant but are less prone to apple scab.
Sometimes replacement is not an option for the owner because the tree has sentimental
value, such as a memorial tree or that by removing it, it will cause too big of a void for
the owner while waiting on a new tree to grow to maturity.
l often recommend timely selective pruning and fungicidal applications for treating
older, less-resistant crabapple trees if the tree is salvageable.
The procedure involves selectively thinning the canopy to provided for better air
circulation for faster drying conditions and penetration of chemicals used to prevent
When | mention selective thinning, | am not implying cutting every interior branch,
because that will cause more harm than good by causing excessive sucker sprouting.
Excessive interior branch removal will cause a lion-tail effect which leads to limb
Chemical applications of a fungicide should be applied between April through early
May for adequate control of the disease.
This procedure should be done yearly, starting as the buds begin to show pink
coloration just before bloom.
The fungicide application acts as a protective coating on the leaf surface during wet
weather that inhibits the fungal disease from setting in.
In summary, the best option for your old crabapple is replacement with a more-resistant
variety, which is more economical in the long run.
If this is not an option, then if the tree is salvageable, perform selective-thinning and
proper applications of a fungicide to maintain optimal health and beauty of your
flowering crabapple trees.
I have included a publication from Purdue University which contains detailed
information about apple scab. APPLE SCAB OF FLOWERING CRABAPPLE TREES (PDF)
If, you need help with chemical applications of a fungicide, then time is of the essence,
because April is past half-over and has been unusually wet — and the forecasts are that
the rains will continue at current levels for some time, which means a BAD SCAB year!
We also can remove the old crabapple tree and replace with a more-resistant variety in
the same location for you.