Spruce spider mite

The spruce spider mite (Oligonychus coniferarum) is a significant pest belonging to the family Tetranychidae. It is a major threat to a variety of coniferous trees, as it feeds by puncturing the cells of the needles and extracting their contents, which causes physiological stress to the host tree.

This pest is primarily found on various coniferous species, including spruce (Picea), juniper (Juniperus), arborvitae (Thuja), and fir (Abies). It is particularly problematic in landscape settings where trees are subjected to environmental stress, making them more susceptible to infestation and rapid decline.

The biological development of this mite is highly dependent on ambient temperature. Overwintering occurs in the egg stage, with eggs attached to the needles and bark. Once temperatures rise in spring, larvae emerge and begin feeding immediately. The species can complete several generations throughout a single season, especially during hot and dry summer months.

Infestation symptoms are characterized by stippling or bronzing of the needles, which eventually turn brown and fall off prematurely. As the population increases, a characteristic fine, delicate webbing becomes visible between the needles and along the twigs. Heavy infestations can lead to significant defoliation and may kill weaker branches or entire young trees.

Integrated pest management (IPM) is essential for controlling Oligonychus coniferarum.

• Frequent monitoring during spring and early summer.
• Providing adequate water to reduce plant stress.
• Using high-pressure water sprays to physically dislodge mites from the foliage.
• Applying horticultural oils or specific acaricides when thresholds are exceeded.