Spots on Japanese maple trees

Asked May 15, 2017, 2:20 PM EDT

We have seedlings under our Japanese maple that we repot and sell. About every year at this time they get the dry spots on the leaves. Can you please tell us why they spot and how if anything we can do to stop?

Virginia

3 Responses

Good Afternoon,

Well... the maple leaf spots have struck again! What can I do to prevent this from happening? 1st, no need to panic regarding the seedlings' health, they will be fine.

I can't quite tell with the Jap Maple foliage being purple, but the condition appears to be eye spot or Phyllosticta leaf spot, a common, but primarily cosmetic disease that affects maples (in particular Amur, Japanese, red, silver and sugar maple). Phyllosticta leaf spot is similar in many ways to other foliar diseases of maple such as anthracnose and tar spot.

These spots have tan to brown centers and typically a purple, red, or brown margins. Tiny, black, pimple-like reproductive structures (called pycnidia) often form within the spots, and are diagnostic. As spots mature, the centers may fall out, leaving roughly circular holes.

This leaf spot is caused by the fungus Phyllosticta minima which overwinters in leaf litter. In the spring, rain and wind move spores of the fungus from the leaf litter to newly developing maple leaves, where infections occur. Spores produced on infected leaves can lead to additional infections within the tree canopy throughout the growing season.

Although leaf spot may look unsightly, the disease is usually only a cosmetic problem, rarely causing significant damage to mature and vigorously-growing trees. Occasionally, the disease may defoliate trees early in the growing season, but these trees are typically able to produce new leaves within a few weeks. Defoliated trees should be watered (about one inch of water per week), and properly fertilized (based on a soil nutrient test).

Compost, bury or burn leaf litter from infected trees in the fall, or in the spring before trees re-leaf. Newly planted maples, and established maples that have been severely affected by leaf spot for several years, may benefit from treatments with a fungicide containing chlorothalonil, copper, mancozeb, neem oil, sulfur or thiophanate-methyl. Three treatments may be needed for adequate control: one at bud break, one when leaves are half expanded, and one when leaves are fully expanded. Be sure to read and follow all label instructions of the fungicide that you select to insure that you use the fungicide in the safest and most effective manner possible.

Happy gardening, JON

Hi Jon,
Thanks for your advise. Is there one product that has these ingredients in the spray or grandulas to be mixed? We would like to see some improvement and are willing to try anything. Also what kind of spray would you recommend for apple tree leaves that have rust streaks on leaves. They also curl up. Thanks!
Barbara Goard in Patrick Springs

Hello,

Yes, the multipurpose garden fungicide called Daconil has the active ingredient Chlorothalonil inside. Another suitable product would be Immunox Multi-purpose Fungicide by Spectracide. Both/or one or the other are available at most box stores, and hometown hardware stores.

Either of these two products would work to control rust diseases and other diseases on apple as well; however, leaf curl is often associated with insect feeding so you may choose to use a Home Orchard Spray instead. Most Home Orchard Sprays are available as a powder for mixing with water in your sprayer. The Home Orchard Sprays also have 2 and sometimes 3 products to offer both disease AND INSECT control. (Just don't spray during bloom)

Hope this helps, JON