What are spider mites?
Spider mites are pests that present a threat to many crops throughout the world. Despite their small size, they are capable of causing severe damage very rapidly due to their great reproductive capacity. There are more than 1200 species worldwide, many of them are common crop pests. The two-spotted spider mite, Tetranychus urticae, is by far the most important species in greenhouses and many outdoor crops.
Spider mite damage
Larvae, nymphs and adults cause damage to the host plant by feeding on plant sap. They mainly occur on the underside of leaves where they pierce the cells and suck out the contents. The empty dead cells become yellow, and in many plants the damage can also be seen on the upper surface of leaves as small yellow dots. The destruction of cells results in reduced photosynthesis, increased transpiration and reduced plant growth. As damage increases whole leaves turn yellow, and as more cell sap is removed, the leaf, and eventually the whole plant may die. The nymphs and adults also produce webs, and plants can be completely covered with such webs in which the mites live. The webbing and spotting on the leaves affect the appearance of the crop. This is of particular concern in ornamental crops.