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Spider mites are one of the most common and devastating plant pests. The grower should take preventative steps against spider mite infestation.
 Species
The Red Spider Mite (Tetranychus Urticae) is one of the more common species of mite. Barely visible to the naked eye, adults are just 0.4mm long. Despite its name only the older females attain a red colour - the majority of red spider mites have a translucent shade of cream, green or brown.
Behaviour & Breeding
Spider mites live and breed on the underside of plant leaves. They eat plant leaves and reproduce at an alarming rate. They can have an almost immediate and devastating effect on the Growers crop. The majority of the spider mite population are female. They lay tiny eggs only 0.15mm long on the underside of leaves. A spider mite population can grow rapidly. One adult female can lay up to 100 eggs and the eggs take about 4 days to hatch. 4 days after hatching a spider mite reaches adulthood - the young adult females lay eggs and the cycle continues. In less than 10 days a plant can be infested with them.
Finding Mites
As the mites are tiny, it's best to look for signs of damage to your plants to determine if you have an infestation. Spider mites feed by sucking fluid from the underside of leaves leaving pin size white/transparent dots on the top surface of the leaf. These dots are usually in clusters. If these spots are present turn the leaf over and (preferably with a magnifying glass) look for tiny mites or mite eggs. Misting the underside of leaves with spray bottle of water will reveal any webbing the spider may have spun. Faded leaves and lots of webbing indicate that spider mites have taken a firm hold on the plant.
Preventative Measures
As with most annoyances prevention is better than cure. Keeping your grow environment clean & controlling environmental variables such as light and air flow is important. Mites can be transferred from person to plant so ensure you change clothes if you have been in an infested area before entering the grow area. Pets can also carry the mites - keep them away from your plants.
Spider mites thrive in hot and dry conditions often opposite to which plants prefer. Whilst keeping the lighting at your chosen level try to keep the heat down and the air moving.
Check your plants and your growing environment on a regular basis (about every 5 days) so you have a chance to act before spider mites take hold.
Things to look for include:
- Overall cleanliness of the growing environment
- Flying bugs, pets and other possible contaminants
- White spots, webbing and the discolouration (lightening) of plant leaves.
- Insects and their larvae within the root zone
Taking action
If after making these checks you suspect you have spider mites, separate the affected plants from the healthy ones and spray with a product like 'Buzz Off'. Keep light levels high, humidity high and temperature low to limit the infestation. We also sell Spider Mite Control products.
Natural Predators
If you were unable to make regular checks and prevent widespread damage try introducing a natural predator of the spider mite to keep them under control.
Phytoseiullius is an effective spider mite predator and can be bought from grow shops. They are usually supplied in small vials often in quantities of 500 or 2000 suspended in vermiculite. Ideally they should be used immediately. If stored keep the vials horizontal and the surrounding temperature about 5 degrees celsius.
Similar in size to the spider mite, an adult Phytoseiullius can devour 8 adult red spider mites per day. Their rate of reproduction is faster than the red spider mite and they prefer a cooler environment reproducing at temperatures below 30 Celsius. They also favour long light cycles and are more effective in 15+ hours of light.
Due to the shorter light cycles of the flowering period Phytoseiullius can be less effective if introduced when the plants are in flower. A combination of spray and predators may more effective under such conditions.
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