APPLE SCAB
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Problem with tree(s)
Here is a before and after picture of two apple trees in an orchard. One has been treated for apple scab and the other has not. You can obviously guess which one was not. It probably looks like your apple tree in July.
OVERVIEW
Ok so we have all seen the pictures to the right hand side of the page. Well that is if you have an apple tree of any variety and do not actively treat it for apple scab. So I will teach you a bit about apple scab and give you some options to take care of this fungal disease. Apple scab is a fungus so it is spread by spores. I will talk about the process near the picture on the bottom that shows the process. Apple scab show up on the leaves of the tree as well as the fruit. It effects all of the apple species and crosses into some other fruit trees as well. Most of these do not grow in Minnesota and for the sake of this page I will focus just on apple scab.
So as you can see it effects the leaves of the tree and the fruit as well. The scabs make the fruit less desirable but does not change the taste or make the fruit bad in any way other than appearance. The damage on the leaves though is pretty obvious and progressively gets worse over year of having this disease spread on the tree. Some people have told me that the disease runs in cycles and that is completely false. Warmer springs will make the fungus spread faster. Dry conditions are also optimal for this disease.
While apple scab does not usually kill a tree it can lead to many other problems in apple tree. Japanese beetles feed on weak apple trees and wood boring insects can often be found in trees weakened by apple scab. While the singular disease may not kill the tree it can be killed by a combination of these problems.
DISEASE CYCLE
Apple scab is a leaf disease and it runs in cycles. I will talk about the disease as it effects a new tree not to confuse you with the knowing what comes first. Its a chicken and egg scenario. So I will make this easy on you. You have a new tree and it is not infected with apple scab. You just planted it and you have another crab apple tree in your yard. It is spring time and is the perfect situation for apple scab to spread into your new tree. The leaves from last years sick tree have been hiding in the space between the grass. The fungus is now fruiting and spores are being formed from the leaves.
These spores spread with the help of wind to the tree above and other trees in the very close proximity. The new tree you just planted has now taken up the spores from your infected tree and now the disease spreads on the newly formed buds and leaves. The disease looks invisible until brown furry like spots start forming on the leaves. These legions spread and turn black often. Then necrosis starts setting in and big yellow spots or the leaves turn yellow completely. After this the leaf dies off and falls off the tree. Often these leaves are mulched into the grass below and hang out on the soils surface waiting for the process to start all over again next spring.
TREATMENT PLAN
Treatment can be done in one of two seasons and the methods of application are done differently. Spraying is the most common way that apple scab is treated. This application method is done in the spring and is done at first bud. Timing is extremely important as chemical does not kill the fungus it prevents it from spreading. Nest application is done two weeks later to make sure the tree has chemical treatment through the time the spores are fruiting. Sometimes a third application will need to be made if the spring season does not come as normal. Most people try to do this method themselves often with no success. This is because they use chemicals that you get at hardware stores. Those do not work so please dont waste your money and make yourself believe that their is no cure for this simple disease.
The second method and often the one I choose is a trunk injection that is done in the fall to prevent the fungus from forming the following year. The chemical lasts in the tree through the winter and is there at first bud with the tree so the fungus cannot spread. Timing must be in the fall before the tree starts to go dormant. It is recommended that you use a professional when it comes to plant health care even if it seems like a simple disease liek apple scab. Contact us by using the form on the side of the page.
