Thuja mite

Systematic position. The Thuja mite (Aculus mosoniensis) belongs to the order Trombidiformes and the family Eriophyidae. These are microscopic, eriophyid mites that are often invisible to the naked eye, requiring specific entomological techniques or high-magnification lenses for reliable identification in the field.

Host plants. The primary host for this species is the Thuja genus (specifically Thuja occidentalis). It is a significant pest in nursery production and landscape architecture, as it can cause extensive damage to hedges and decorative plantings, leading to significant economic losses for growers and homeowners.

Biology and life cycle. These mites overwinter as adult females sheltered within the scale-like leaves or buds of the host plant. As spring temperatures rise, they emerge to lay eggs. Under favorable conditions, the mite completes its life cycle in a short period, resulting in multiple generations per year. Dispersal is largely wind-borne or through contaminated plant material trade.

Nature of damage and harmfulness. The feeding activity of Aculus mosoniensis causes the foliage to lose its vibrant green color, turning yellowish, bronze, or brown. The needles become brittle, and in severe infestations, heavy shedding occurs. Because the damage resembles physiological drought or fungal diseases, it is often misdiagnosed, leading to ineffective treatment.

Control measures. Effective management depends on early detection and the use of targeted acaricides. Integrated pest management strategies are recommended:

• Conduct regular inspections of the inner canopy, especially on the sunny side of plants.
• Apply chemical control using systemic acaricides during the active growth phase.
• Ensure proper plant spacing to improve airflow, which creates less favorable conditions for mite proliferation.
• Avoid overly dry planting sites and ensure adequate soil moisture to strengthen plant health.