The aromatic bay laurel, or Laurus nobilis, is an evergreen Mediterranean herb that tolerates frost and makes an excellent indoor potted plant and culinary herb. Unfortunately, the bay laurel is also an enticing species of plant to a few insects that enjoy making meals of the bay laurel's glossy green leaves and nourishing sap.
Examine each leaf carefully looking for a clear sticky substance that usually indicates the presence of scales, small insects of evergreens and deciduous plants. Wear garden gloves while performing this task. Identifying leaf damage caused by insects is not complicated thanks to the telltale signs of the scales and plant lice that occasionally affect the leaves of bay laurel trees. If you detect a substance, it should smear easily with a swipe of a gloved index finger.
Scrutinise the underside of the leaves for spots and changes in texture. Damaged leaves will appear spotted with small brown clusters of raised bumps that are actually the scale insects. These insects can also appear on the stems of a bay laurel and cluster much in the way that aphids cluster on top of each other along plant stems. The bay leaves will also appear brown on the edges in some cases.
Inspect the bay laurel leaves carefully with a magnifying glass for tiny black, white, green or brown specks. Insects classified as Trioza alacris, or jumping plant lice, are extremely small pests that commonly feed on the sap of the bay laurel trees, causing leaf damage in the process. Known as bay sucker, the infestation is usually most obvious in the form of browning, unhealthy leaves.
Look closely at the bay leaves for dry or curling edges. Damaged bay laurel leaves will appear curled at the margins and they sometimes turn yellow where jumping plant lice are present. According to the article "Pest and Disease of Bay Laurel Tree" on the Garden Action website, plant lice can multiply quickly, often producing three generations on severely afflicted trees.
Explore the base of the bay laurel tree. An abundance of dropped leaves that have browned entirely is another sign that jumping plant lice might be present. Leaves that appear thicker and yellowed are doing so because of areas where the insects are concentrated. Damage still in progress is equally notable on the underside of bay laurel leaves still attached to the tree.