Red Spider Mite (Tetranychus urticae)
What is known in the world of cannabis and gardening in general as a plague of spider mite is the attack of red small spiders, which have a size of about 0.5 millimeters, being really hard to see with the naked eye. They usually settle in the back of the leafs (underside). They aren?t easy to perceive at simple sight, therefore that’s why the first thing that we will probably perceive are the symptoms.
How to detect a plague of spider mites?
The first evident symptoms are a few white spots like pin tips, which accumulate throughout the main vein structure of the leaves and can even finish up discolouring them, aquiring a light greyish green. This would be the first phase of the pest.
In the second stage, the leafs will completely discolour and can reach to fall; in this second phase we can perfectly see fine spider webs on the underside of the leafs.
The last phase of colonization is when plants are fully covered by red spider webs. The plant will surely die if it gets to this point.
How, when and why breaks out this plague in marijuana plants?
Red spider mites in outdoor growing:
Outdoors, spider mites usually attack mostly at marijuana plants which suffer periods – of shorter or longer lenght – of drought, and which are also subject to high temperatures and very low humidity; the ideal conditions for the development of spider mites is with high temperatures and dry enviroments. That is why we?re faced with this problem especially during the months of July and August, when the best conditions for the spread of this pest are naturally given. If we add to these atmospheric conditions a plant grown in a small pot and with little or irregular irrigation, we have the perfect cocktail for the propagation of spider mites.
Plants behind glazed galleries are especially problematic.
Although the spider mites pest can significantly decimate the harvest, it will rarely end with the entire crop, since plants attacked by red spider mites – unless they are covered by spider webs – will still be suitable for consumption.
Red spider mites in indoor growing:
Indoors, red spider mites are one of the most common pests, with an alarming destruction capacity of the crop, because indoor crops, under artificial lights, are usually under the combination of high temperatures and low humidity.
In this growing system is where the plague can completely destroy the harvest, since – being an indoor growing – there aren?t the predators that would be found in natural ecosystems.
As happens outdoors, July and August are the months when plants are especially prone to the expansion of the spider mites plague, when the high temperatures of the summer join with the heat produced by the growing lamp, what raises the temperature to 33 / 34 ° or higher.
Control and prevention of red spider mites on marijuana crops
To prevent their presence, the best method is to regularly wet the foliage of the plants by spraying them with water with a hose, by aspersion or in the case of indoor plants, with a hand sprayer or the installation of ultrasonic humidifiers ; placing some containers full of water to increase humidity may also give some result. It?s also necessary to be careful when using fertilisers rich in Nitrogen (N), which favours this pest since plants grow much more and have lots of very tender tissues, ideal to be bitten by this parasite.
We can find on the market different products that can help us fighting against spider mites once the plague has spread, but we will achieve the best results using these products as prevention, that is the only way to keep our crops free of spider mites. For example:
- Neem Oil Extract (Ain thc, azaprot)
- Natural Piretrines (Expelex, pireprot)
- Nettle Slurry with potassic soap (Urtifer with bioleat)
Besides these commercial products there are also homemade remedies to combat this plague, for example:
- Onion skins placed on the soil of the crops act as repellent
- Infusion of ferns diluted in water to apply at the beginning of spring
- Infusions of wormwood mixed with soda silicate, sprayed in spring and autumn
Another way to control this pest is the manually. It consists in cleaning the underside of the leafs with a cotton ball dampened with pharmacy alcohol diluted with water at 50%. Notice that if we decide to use this system, we will have to repeat the operation every week until the end of the crop.
We can find on the market different types of predator insects against spider mites:
- Amblyseius californicus: Mite predator of red spider mites
- Feltiella acarisuga: Gall-Midges predator of red spider mites
- Macrolophus caliginosus: Bed Bugs Nymphs predator against red spider
- Phytoseiulus persimilis: Mite predator of red spider mites
Unfortunately, when the plague has escaped from our control and seriously threatens the development of our crop, we have no other choice than combat it with chemicals. In this case, we must look for an acaricide that has low danger for the fauna and a short safety term. The Doble action acaricide , from COMPO, works great for this purpose.