Citrus
Spider Mites
Tetranychidae
Mite
In a Nutshell
- Tiny spots on leaves.
- Small webs between stem and leaf.
- Dried out leaves.
- Tiny, pale green, oval mites.
Citrus
Symptoms
The spider mites feeding causes white to yellow speckles to form on the upper surface of the leaves. As infestation becomes more severe, leaves appear bronzed or silvery first and then become brittle, rip open between the leaf veins, and finally fall off. Spider mite eggs can be found on undersides of leaves. The spider mite itself is located there, nesting in a cocoon resembling webbing. Infected plants will be covered by a web spun by the spider mites. Shoot tips can become bald and as a result, side shoots start to grow. In cases of heavy damage, the quantity, as well as quality of fruits, is reduced.
Recommendations
Organic Control
In case of minor infestation, simply wash off the mites and remove the affected leaves. Use preparations based on rapeseed, basil, soybean and neem oils to spray leaves thoroughly and reduce populations of T. urticae. Also try garlic tea, nettle slurry or insecticidal soap solutions to control the population. In fields, employ host-specific biological control with predatory mites (for example Phytoseiulus persimilis) or the biological pesticide Bacillus thuringiensis. A second spray treatment application 2 to 3 days after the initial treatment is necessary.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. Spider mites are very difficult to control with acaricides because most populations develop resistance to different chemicals after a few years of use. Choose chemical control agents carefully so that they do not disrupt the population of predators. Insecticides based on wettable sulfur (3 g/l), spiromesifen (1 ml/l) or abamectin can be used for example (dilution in water). A second spray treatment application 2 to 3 days after the initial treatment is necessary.
What caused it?
Damage is caused by spider mites from the genus Tetranychus, mainly T. urticae and T. cinnabarinus. The adult female is 0.6 mm long, pale green with two darker patches on its oval body, and long hairs on the back. Overwintering females are reddish. In spring, the females lay globular and translucent eggs on the underside of the leaves. The nymphs are pale green with darker markings on the dorsal side. The mites protect themselves with a cocoon on the underside of the leaf blades. The spider mite thrives in dry and hot climates and will produce up to 7 generations in one year in these conditions. There is a wide range of alternative hosts, including weeds.
Preventive Measures
- Plant resistant varieties if available.
- Monitor your field regularly and check the underside of leaves.
- Alternatively, shake a few insects off the leaf surface onto a white sheet of paper.
- Remove affected leaves or plants.
- Remove nettles and other weeds from fields.
- Apply water to pathways and other dusty areas at regular intervals to avoid dusty conditions in the field.
- Water your crop regularly as stressed trees and plants are less tolerant to spider mite damage.
- Control the use of insecticides to allow beneficial insects to thrive.
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