Plant Doctor Archive

A mitey problem

I think I have spider mites on some of my plants. How can I tell that they are, in fact, spider mites, and what can I do to get rid of them?

Mites, because each individual creature is so tiny, are some of the most difficult-to-identify garden pests. And note that I said creature, not insect, because, in spite of a superficial similarity, mites are not insects.

Mites are more closely related to spiders than insects. In fact, the two-spotted mite, the pest that is most often found infesting our garden plants, is sometimes known as 'red spider' because, like a spider, it has eight legs, and because its body changes to an orange/red colour in winter.

This confusion of common names sometimes causes innocent spiders to be falsely accused of being a garden troublemaker. A suspicious gardener, on sighting a tiny red spider, is likely to wonder if this is the dreaded pest about which he´s heard so much. The easiest way to resolve this is to point out that, if the spider is easily seen with the naked eye, it´s not a two-spotted mite (and is more likely to be a garden friend).

Two-spotted mites are very tiny. So tiny that they´re quite difficult to see with an unaided eye. But if you have good eyesight, in good light the two dark spots on the body stand out clearly.

What to look for

Usually the first sign you´ll see of mite presence is the damage they cause. The two-spotted mite is a sapsucker that works from underneath the leaf, sucking out the leaf´s green cells. Damaged leaves turn yellow or brown and their surface has a papery, slightly gritty feel.

As mite numbers build up, their damage becomes more obvious. A layer of fine webbing appears on the underside of affected leaves and may eventually cover the entire leaf. The tiny mites can be seen scrambling on the webbing.

How to control two-spotted mites

Wet them: Like many other garden pests, two-spotted mites flourish in warm, dry conditions. One of the best ways to keep numbers under control is by spraying water over the plant material. A regular mist spray can discourage up to 50% of a population of two-spotted mites.

Oil them: White oil is registered for control of mites. Good spray coverage is essential because white oil works by smothering the pest and blocking its breathing processes. Avoid spraying any type of oil when temperatures are high.

Miticides: Some insecticides (but not all) will control mites. Mavrik is a very low toxic insecticide/miticide that is doubly effective because, as well as controlling on contact, it has a good repellent (i.e., it makes the leaf surface unpleasant for the mite) action.

As with any other form of garden pest control, prevention is better, and more desirable, than cure. Avoid growing plants in constantly dry situations (such as beneath overhanging eaves) and keep plants well-fed and free from water stress.

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

Reproduced with permission from NZOOM Home and Garden content, from the previous website of  The views expressed here are not necessarily those of the RNZIH   HOME AND GARDEN   Plant Doctor Archives Main Page