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Did You Know?
There are over 110 varieties of Crabapple trees in Illinois, even though only four basic colors are evident. Of those 110 varieties, about 50% are highly susceptible to Apple Scab, 25% are somewhat susceptible during wetter springs and 25% are not susceptible at all.

acrobatDownload the Tree Green "Apple Scab" brochure (287KB)

How Tree Green was able to take Crabapple trees with infected with apple scab disease and bring them back to health.


Apple Scab Disease of Crabapple

In spring, Crabapple owners have the most beautiful trees in the neighborhood. These trees are gorgeous with their red, purple, pink or white flowers, and a pleasure to own. But by July, many are very unsightly, appearing mostly dead, which ruins the aesthetics of the landscape.
That is because during the spring budding and flowering cycle, Crabapple trees are under attack from a microscopic windblown spore that will attach itself to the tree’s leaves on damp days, causing severe leaf damage as the summer progresses. The fungal spore comes from infected fallen leaves from the previous season. The spores released in early spring can blow in the wind for miles, searching out their host Crabapple plant. 

When leaves are dry, the spores bounce off harmlessly. But, on days where rain or even morning dew are present, the spore is able to attach itself to the leaf and the damaging process begins again. Cool, damp springs are the 'norm' in Illinois, which is why our susceptible Crabapples always look unattractive, if not dead by mid-Summer.

In May & June, Apple Scab initially appears as olive green, velvety spots ¼” or more in diameter. As the disease progresses, the leaves turn yellow and brown, and shortly thereafter, fall to the ground. Susceptible Crabapple varieties can become 50% to 100% defoliated by mid-July.

apple scab TREATMENT
Although trunk injections are available, Tree Green prefers a foliar spraying process. Yearly injections cause too much trunk damage and should only be used as a measure of last resort (when spraying is not a viable option). 

Spraying for Apple Scab is a viable option if the best products are used and the timing of the applications are impeccable. When a high quality fungicide is applied to the leaves at the proper times, it will kill the microscopic spores before they can ingrain themselves into the leaves.


  1. Raking the leaves thoroughly from around your Crabapple will prevent the disease the following year. This is questionable in our opinion, and in no way should substitute a quality tree spraying program. 

    Case In Point . . . Most homeowners dispose of their leaves every Fall. Yet we deal with Apple Scab on a yearly basis. The problem is that fallen leaves are hidden in bushes, mulch and groundcover plantings. Plus, the spore can blow for up to 5 miles – so your Crabapple is always at the mercy of every other homeowner’s clean-up techniques (or lack thereof), upwind of you.

  2. Fungicide sprays applied as late as June or July can stop the spread of the disease once it has already set in. This is absolutely false! Fungicides work on a prevention-only basis, never an eradication basis! Crabapples treated by Tree Green receive a total of 3 spray applications each year, performed in early spring.

    Every year in June & July, we explain to new callers that we won’t be treating their Crabapple trees until the following spring. Often these potential new clients question us, explaining that another company wants to treat their tree right now to “stop the progression of the fungus”. Any company promoting this either doesn’t know their business or is flat-out deceiving you.

  3. Apple Scab Disease will not kill the Crabapple tree. Apple Scab Disease may not kill your tree quickly, but over an extended period of time it very well may. All trees need to gain and build energy from the sun absorbed through a full crop of healthy leaves. When a Crabapple defoliates due to the disease, it is unable to absorb the needed sunlight throughout a big part of the summer causing gradual weakness in the overall health of the tree. Our 40 plus years of experience has proven to us that this cumulative weakness does indeed kill Crabapple trees.

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