Treating apple scab in crabapples #743248 - Ask Extension


Treating apple scab in crabapples #743248

Asked April 08, 2021, 11:45 AM EDT

We have two Prairiefire crabapples that we planted with the understanding they were scab resistant, but an arborist identified apple scab in them about three years ago and has sprayed them each spring. They now are scheduling again for this spring and we are wondering if it is advisable to continue the spraying or not. We have not seen evidence of scab the last couple of years but cannot be abaolutely certain there isn’t some of the fungus around.

Hennepin County Minnesota

Expert Response


Thank you for contacting Ask Extension.

Apple scab is common in Minnesota, so chances are, the pathogen spores are around your garden every year. However, some years apple scab infection on the trees is worse than others. If we are having a dry summer, we will see very little apple scab infection. In a wet year, we experience more apple scab. Last year for instance, the summer was very dry and we had minimal to no apple scab in Minnesota orchards. This year is predicted to also be drier than normal in Minnesota. You should also know that a little bit of apple scab on a tree is not devastating. You will still get a good crop even if a little bit of apple scab is present. However, large infections can definitely lead to a lot of inedible and disappointing fruit.

Resistant variety does not mean that it will never get apple scab. It only means that it is less likely to get apple scab than other varieties.

Armed with all this information, it is up to you whether or not to continue to spray for apple scab every spring. It is present in the environment, but won't cause infections on the trees every year. This year has a lower risk of apple scab than others, if dry weather predictions turn out to be true. If it is important to you that you do everything you can to eliminate the chance of apple scab, then continue having them spray annually. If you are ok with a little bit of scab, and want to reduce chemical inputs, you could consider telling them not to spray if the season is predicted to be very dry.

Hope this helps.

Jackie Froemming Replied April 08, 2021, 1:28 PM EDT
Thank you so much, Jackie.  It does indeed come down to a question of whether to add more chemicals to the environment.  I think we are basically inclined to take a pass this year and hope for the best.  

I am an old Extension person myself so always trust the advice I get from this source.  I was a county agent in Rochester NY 1972-76, then moved to Ithaca and worked with Extension for several more years at Cornell University before moving on to other positions on campus.  I'm not a pomologist or horticulturist, though, so I have to depend on you experts.  I do appreciate your taking the time to steer me in the right direction on this question.

With gratitude,

On Thu, Apr 8, 2021 at 12:28 PM Ask Extension <> wrote:
Lani Peck Replied April 08, 2021, 1:38 PM EDT

Glad to be of assistance.  

Jackie Froemming Replied April 08, 2021, 1:44 PM EDT

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