Spots on Crabapple Leaves: What's Playing Malice With My Malus?

July 20, 2009


Oh dear. Japanese beetles on my roses. Slugs (until I limed them away) on my hostas. And now, something is spotting my lovely, plum-colored crabapple, Malus ‘Royalty.’ What’s to blame? Is it a fungus — or too much rain?

The culprit, in fact, is “apple-scab,” or Venturia inaequalis, a fungus that is quite common on both apple and crabapple trees. You can recognize its presence by the brown-to-olive spots it makes on the veins of leaves — leaves which inevitably turn yellow and drop.

Can you guess what venturia needs to survive? Wet weather. Yes, the same soggy conditions that we who live in the Northeast have endured for the last six weeks. Frankly, I’m surprised the fungus hasn’t defoliated entire apple crops in this region. Maybe it has.

Prevention, or perhaps I should say control, of apple-scab needs to begin in autumn, with a thorough cleanup around trees. Otherwise, the fungus overwinters in fallen, infected leaves, and then joyously springs to life during the first rains of April.

Fungicides help, but for environmental reasons I do not like them. Furthermore, they have to be sprayed at two-week intervals begining at bud-break in the spring, and spraying must continue through all periods of wet weather. You might feel differently about using fungicides.

It is fortunate that the crabapples I selected for this property — ‘Sergeant,’ ‘Madonna,’ and the aforesaid ‘Royalty’ — are all scab-apple-disease resistant. Damage has been limited to only a few patches on Royalty, and these patches I will merely cut off. And even should the disease become rampant, and a tree become defoliated, well, that’s not much of a problem. True, scab-apple can destroy the beauty of a tree for one season, but rarely is it fatal. Most trees, whether they are disease-resistant or not, recover the following year.

Are any of your own trees the victim of scab-apple? Or is something else bugging them (or you)? Share your own, personal horror-stories in the comments section below.

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Related Posts:
Hostas: How to Keep Slugs and Snails Away

Comments

  1. greg says:

    Kevin, my crabapple has your malice X 2: scab apple fungus AND japanese beetles! The beetles are skeletonizing many of the leaves. I don't spray, either, though. I've come to expect these problems sooner or later every summer. The tree is always fine the next spring.

  2. Katreader says:

    My enemy is the Japanese Beetle. I despise these vicious monsters. They get into everything-privet, grapes, apple tree, ornamental plum, rowan, and they eat the buds of my roses of sharon. I used grub control on the lawn in the fall-but they're back. Any suggestions on how to get rid of these guys would be greatly appreciated.

  3. Greg – welcome! I hate 'em, too!

  4. Katreader: Are you talking about…ALL-OUT-CHEMICAL-WARFARE? If so…Bayer Tree & Shrub contains imidacloprid, a chemical that enters the tree or shrub systemically (through the roots). If a jb eats a leaf, the jb dies. Just don't use it on anything YOU intend to eat!

    I should probably do a full post on this topic later. In the meantime, hope this helps!

  5. Katreader says:

    LOL All out chemical warfare sounds good…but some of the things they get into, I will eat and I'm concerned about my dog getting into anything. It's a thought for the front yard though. I look forward to a full post about these creatures.

  6. Judy says:

    Beetles, fungus, crabapples — oh, my! And I thought city life was tough. Would these critters ever find their way to your lovely indoor gardens? Or are they strictly the outdoor type?

  7. Judy – mercifully Japanese beetles confine themselves to outdoor life. I assume you have them in Central Park…there are a lot of roses in the Shakespeare Garden. Oh, how I miss that place!

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