Fusarium Wilt in Japanese Maple

Japanese maple infected wtih fusarium wilt

Fusarium wilt can impact deciduous shrubs and trees, including plants like maple, redbud, tulip trees, various annuals and perennials, as well as other plant species found in the Treasure Valley.

This disease is most commonly observed in Japanese maples, and we feel it’s crucial to inform Treasure Valley residents regarding this problem. While it is extremely prevalent in Japanese maples, it poses less of a threat to shade-type maples. Fusarium wilt is a soil-borne pathogen that can persist for many years, reportedly up to 7 years in the soil. The disease causes leaves to wilt by obstructing the transport of water and essential nutrients for the tree's survival.

One of my neighbors encountered fusarium wilt a year or so ago, which killed his beautiful Japanese maple. About a year later, one of my three Japanese maples succumbed to this disease, and now the neighbor is losing another Japanese maple.

The disease enters through the roots and disrupts the water-conducting vessels. Symptoms include fading leaf color, often turning leaves yellow to brown. These symptoms typically appear later in the year. The disease does not always affect the entire tree simultaneously. You might notice a branch or two looking pale, as though lacking water. At other times, it can kill the entire tree swiftly. The plant's age can influence how and when it is affected. It’s not uncommon to have several plants of the same species nearby, with one dying immediately while another survives for years without symptoms.

There is another disease called verticillium wilt, which appears almost identical to fusarium wilt. Both diseases are fatal, and laboratory diagnosis is required to determine the exact cause. Regardless, both diseases will kill the affected plant. During cool weather, microsclerotia produce hyphae that infect the plant's roots. The pathogen then moves upward as the weather warms, causing the described effects. There really is no cure for fusarium or verticillium wilt other than removing the infected plant. However, you may be able to mask the problem for a time.

Pruning

The best approach is to remove the entire tree, cutting it close to the soil and carefully removing all parts to avoid affecting nearby plants. After removal, dig out the roots and remove as much surrounding soil as possible. Replace the removed soil with fresh topsoil. If possible, leave the soil unplanted for a year or choose plants not affected by fusarium/verticillium wilt.

Tool clean-up

Exercise caution after removing the infected plant. Clean all tools used in the removal with bleach, then spray each tool with WD-40 or a similar oil to prevent rust. Tools left unprotected can cause the spread of the disease to other plants.

Charlie H. - Idaho Certified Nurseryman