Hydrangea spider mite

The hydrangea spider mite (Tetranychus hydrangeae) is a member of the Tetranychidae family within the order Trombidiformes. This pest is a specialized herbivore that primarily targets hydrangea plants, piercing the plant cells and consuming the sap, which leads to significant physiological stress for the host plant.

While the mite is named for its preference for hydrangea species, it can infest various ornamental plants grown in greenhouses or home gardens under favorable conditions. These mites typically inhabit the underside of leaves, which provides a microenvironment protected from environmental fluctuations and direct application of some treatments.

The life cycle of Tetranychus hydrangeae involves eggs, larvae, protonymphs, deutonymphs, and adults. The entire developmental process is highly sensitive to temperature; warm, dry conditions significantly shorten the life cycle, allowing for rapid population growth and multiple generations during the growing season.

Damage symptoms usually begin as tiny, pale speckles on the upper leaf surface, commonly referred to as stippling. As the infestation progresses, leaves become chlorotic, lose their natural color, and may eventually wither and drop. The presence of fine webbing covering the leaf undersides or extending between leaves is a primary indicator of a severe mite outbreak.

Controlling this pest requires a strategic approach that integrates cultural practices with chemical interventions. Because spider mites thrive in dry conditions, modifying the environment is key to suppression. Recommended management strategies include:

• Maintaining adequate humidity levels to discourage mite reproduction.
• Regular monitoring of foliage, particularly the undersides of leaves.
• Removing and destroying severely infested plant material.
• Applying specific acaricides or miticides, ensuring full coverage and rotating chemical classes to prevent resistance.