Caterpillars on redbud

(Question)

Hello, I have just noticed web-like nests of small yellow caterpillars on the branches and leaves of my Eastern redbud. At the same time, I saw that many of the tree’s leaves have curled/ruffled edges, the veins are yellow and the leaves have many areas that are yellow. I’ve pruned off some of the nests, and sprayed soapy water on others (in hopes of not having to remove too many branches from the tree). Can the caterpillars be responsible for the mishaped/coloured leaves, or do I have 2 separate problems, and if so, what is the cause of the leaves looking so strange? Many thanks.

(Answer)

Eastern redbud has relatively few pests. The plants may experience some insect damage from leaf rollers, treehoppers, scales, leafhoppers, aphids, and spider mites, but damage is rarely severe.

Your Eastern redbud (Cercis canadensis) might be suffering from leaf rollers. Leaf rollers are moth larvae and can be light green/yellow or light brown. They wrap the leaves around themselves for protection. You were right to handpick and destroy caterpillars, any rolled leaves and cocoons. Further action should be taken to prune out and destroy active webs, preferably when still small.

Bacillus thuringiensis (BT) is an effective control for recurring problems, particularly if applied as soon as larvae hatch. BT is a naturally occurring bacterium that causes illness and death in various insect larvae, including caterpillars of pest species such as gypsy moth, spruce budworm, cabbage looper; will also affect a number of beneficial insect larvae. In addition, leaf rollers can be controlled through the use of pheromone traps and be sprayed with horticultural oil. Targeting pests at the right time with the right product can save you money, make your pest control program more effective, and help preserve the beneficial organisms on your farm.

Ask your local nursery or a certified arborist about these control methods and the best time to implement in your area.

As a side note, redbud is a tree that is particularly vulnerable to herbicide damage, such as those in the formerly allowable lawn “weed and feed” type products. Some of the symptoms you describe (yellowing veins, curling leaves) are symptomatic of this.