What is Wrong with My Crabapple Tree?

Written by: Maria Panasuk, ISA Certified Arborist WI-1479A

Posted: 2022 | Disease Treatment | Spring

Are the leaves on your crabapple dropping off early and covered in funky spots? This is most likely the result of Apple Scab, a common leaf fungal disease. This disease can affect any tree in the rose family, but crabapples are a popular tree in our landscape and are therefore affected the most widely.

A leaf infected with apple scab

How does it start?

Spring moisture on young leaves provides an ideal infection point. It first appears as small olive to brown spots. As the disease matures, the spots get larger and become a darker shade of brown. The infection will reduce the productivity of the leaf, stressing the tree, and result in the tree shedding its unproductive leaves early. Some older varieties of crabapple can lose most of their leaves by mid-summer. Apple scab does not kill your tree, but repeated infections, continued leaf loss, and stress will reduce its overall health. A tree with declining health, loss of vigor and reduced growth leave it susceptible to other insects and diseases.

How does it spread?

This fungus lies dormant in the winter on fallen diseased leaves. In spring, the wind and rain transport the released spores into the environment and onto your tree. Rainy, wet springs and summers are perfect for apple scab to establish, grow, and spread. Once on the tree, it only takes a week or two for new spores to be produced and released back into the canopy. The cycle of infection can occur multiple times throughout a wet season.

A crabapple tree in full bloom!

What can I do to protect my tree?

Chemical applications twice a season are a great way to reduce infections. Most seasons, two treatments are sufficient: once as the new leaves emerge, and a second time when the tree puts out secondary growth. The product we use inhibits the fungus from establishing on the leaves. In addition to spraying your tree, you can clean up the infected leaves in the fall and prune the tree for better wind and air flow. Allowing more air to move through the canopy helps reduce the moisture level in the tree, making it more difficult for the fungus to establish.

Want to avoid treatments?

To avoid spraying susceptible trees annually, removing and replanting is another option. There are several options for resistant variety crabapples, such as ‘Prairifire’, ‘Tina’ and ‘Red Jewel’. Another option is to remove the tree and plant a different type of tree in its place. A redbud is a nice alternative to a crabapple. It blooms at the same time, has a similar mature size, and does not require annual maintenance!

If you have an important crabapple on your property, we can help you. Contact your Wachtel Tree Science arborist today to schedule an appointment and discuss the options for your tree!