Why Does My Apricot Tree Have Red Spider Mite?

Red spider mite (Tetranychus urticae) is a significant pest of wall-trained apricot trees in hot, dry summers. The mites are too small to see easily with the naked eye but their damage — fine yellow stippling or mottling on the upper leaf surface, bronze discolouration across large areas of foliage, and the characteristic fine webbing on the underside of heavily infested leaves — is unmistakeable. Severe infestations can cause early leaf drop and significantly weaken the tree.

Identifying red spider mite damage

The mites themselves are just visible as tiny moving dots on the underside of leaves — orange-red or pale green depending on the season. The first symptom visible to the naked eye is fine yellow stippling on the upper leaf surface — each stipple mark is a feeding puncture. As the infestation intensifies, the stippling merges into a general mottling, then the leaf takes on a bronzed or bleached appearance, and fine silky webbing appears on the underside. In severe cases, leaves drop early and the tree looks scorched.

Why wall-trained trees are worst affected

The south-facing microclimate behind a wall-trained tree is hotter and drier than the open garden. Red spider mite reproduces rapidly in heat and is deterred by humidity and moisture. Trees watered at the wall base and never misted on the foliage create perfect mite conditions. Increasing air humidity around the foliage — by misting the underside of leaves with water on hot days — disrupts this and slows mite population growth.

Natural predators

Phytoseiulus persimilis, a predatory mite sold commercially for biological control, is highly effective against red spider mite. Introduce it to the tree as soon as the first mite colonies are spotted, in warm conditions (above 18°C). Avoid all broad-spectrum pesticide use near the tree — this kills the natural predator population and allows mite populations to explode without check.

Chemical control

Where biological control is not practical, fatty-acid-based insecticides or plant-oil sprays applied thoroughly to the underside of leaves knock back populations. Multiple applications at five-day intervals are needed. Conventional acaricides (e.g. bifenazate) provide rapid control in severe infestations.