Hello,

Based on the images that I have seen, there appear to be other issues. Dealing with multiple issues on a crab apple tree can be challenging, especially when the tree is large. Here’s a comprehensive approach based on the information from educational sources:

Apple Scab:

Fungicides: Proper timing of fungicide sprays is crucial for controlling apple scab. Expect to apply two well-timed fungicides in the spring.

Resistant Varieties: Planting disease-resistant varieties is the best long-term solution to manage apple scab.

Sanitation: Clean up fallen leaves to reduce the source of infection for the next season.

More information is at these links:

Apple scab - Integrated Pest Management (msu.edu)

Apple scab of apples and crabapples | UMN Extension

Bark Splitting:

Wound Care: Tracing around the wound with a sharp knife to remove loose bark may stimulate the growth of the cambium and speed healing.

Avoid Late Fertilization: Avoid fertilizing late in the growing season, as this may promote new growth and predispose the tissue to winter injuries.

More information at this link:

barksplitting.pdf (cornell.edu)

Mealy Bugs:

Insecticidal Soaps: Contact sprays using insecticidal soaps are effective against the mealybug crawler stage, provided coverage is thorough. You may need two to three treatments at 10–14-day intervals.

Beneficial Insects: Use insect growth regulators when beneficial insects are present to avoid harming them.

More information at this link:

Mealybugs – Wisconsin Horticulture

Since you mentioned the tree is too large to inspect or spray entirely, you might consider contacting a certified arborist or a tree care service. They have the equipment and expertise to treat large trees effectively and safely. Additionally, they can provide a proper assessment and ongoing care plan tailored to your tree’s specific needs. Managing these issues is often a multi-step and ongoing process, so regular monitoring and care are essential. You can consult a local certified arborist for a more detailed onsite assessment and personalized advice. To find a certified arborist in your Zip Code, go to this link:

Find an Arborist (treesaregood.org)

If you want a confirmed and precise identification of the problem, you can send all your images by e-mail to the MSU Plant & Pest Diagnostics Lab. The experts there can also provide you with the best treatment options. Their email is <personal data hidden> - Please include your name – The lab will let you know if they need a sample sent. FYI – The lab may also ask for additional images.

Their website is at this link:

Plant & Pest Diagnostics (msu.edu)

Their Contact Information is at this link:

Contact Us - Plant & Pest Diagnostics (msu.edu)

This link will explain the details of submitting a sample to MSU Plant & Pest Diagnostics Lab:

Submit Samples - Plant & Pest Diagnostics (msu.edu)

I hope this helps!