Why Is My Holly Tree Turning Yellow?

The holly tree is a hardy plant that prominently displays its glorious green leaves for most of the year. At Christmastime, the plant is especially handsome, as it features beautiful red berries. Capable of withstanding harsh elements and even high pollution zones, this plant can flourish in a wide range of landscape environments. But, every once in a while, a holly tree's leaves can start to turn yellow, much to the dismay of its owners.

Although capable of withstanding a lot of external forces, the holly tree is especially susceptible to holly leaf miners (Phytomyza ilicis). Leaf miners are the larvae of a wide range of insects that live between the epidermal layers of the leaf.

Leaf miners eat away at the leaf between its layers, making them very difficult to see and eradicate. Depending on the type of miner that has infested the leaf, the signs may include a winding feeding tunnel or a yellow/brown blotch on the surface of the leaf. The damage to the leaf causes it to age faster than its non-infested kin as it turns yellow and eventually falls off.

Although leaf miners very difficult to manage, there are a few things holly owners can do to try and prevent their prized plants from becoming victims of these insects. First, if you notice signs that your tree may have leaf miners, pick any affected or fallen leaves and burn them immediately. In early May, apply trichlorfon, chlorpyrifos, carbaryl or diazinon into the soil at the base of the tree. This will allow the tree's roots to absorb the chemicals, which will kill the miners inside the leaves. Spraying acephate, imidacloprid, dimethoate or oxydemeton-methyl directly on the plant will also help to stem the infestation. However, when the mines created by the larvae are half-formed, stop using the insecticide, as it is during this time when the insect's natural predator, the wasp, will attack and eat a great number of larvae.