Twisted and curled leaves on cherry, plum or apricot bonsai call for immediate attention. If you’re lucky, the problem is merely an insect: check within the curled leaf for tiny greenish or black aphids, which can be removed by hosing down the plant thoroughly and spraying with insecticidal soap.

Leaves that are twisted, puckered and reddish in hue may be infected with peach leaf curl. This fungus causes the leaves to fall off. A second set will grow, but may also be infected. Watering at the pot base, instead of overhead spray, sometimes prevents the fungus from attacking the second growth. The only sure cure is to spray after fall leaf drop (around November) with copper-based fungicide spray.

On the Ume (Prunus ume), curling leaves may signal fusarium wilt. A way to be sure is to cut a branch to see if there is a yellowish-brown ring replacing normal green tissue under the bark. Other symptoms include dieback and the wilting of young shoots, often on just one side of a plant. Extremely hot weather may trigger the symptoms.

Fusarium is a soil-borne disease, and often happens when ordinary garden soil is included in your potting mix. Drenching the soil and plant with a fungicide may save the tree, and you should surely repot it next winter in clean soil. At that time, trim off dead roots and branches, dipping your shears into a sterilizing solution (one part household bleach and nine parts water) between each cut.

(July 1994)

Tag: pests