The bay tree (Laurus nobilis), known for its shiny leaves and yellow flowers, is often used as a landscape tree. They can grow to about 10 feet and have fragrant leaves. However, if these leaves turn yellow it could be the sign of a problem.
Yellowing leaves are a sign of an infestation of insects known as bay suckers or jumping plant lice. While these insects are not deadly, they do affect the tree by feeding on it and turning leaves yellow.
Thiacloprid is an insecticide that can treat bay suckers if applied early. If you allow bay suckers to remain on the tree, they can lay eggs, which feed on the sap and cause even more damage. Do not use leaves for cooking when treated with insecticide.
If left untreated, bay suckers can severely weaken your bay tree. While they don't kill the tree, the weakened tree becomes more susceptible to diseases and other pests that can prove fatal.