Red Spider
The red spider mite is one of the most common pests in cannabis crops. High temperatures and low relative humidity are the main factors influencing the rate of red spider mite population growth.
Temperatures below 15°C and above 40°C are unfavorable for the spider's development. Average temperatures of 28-30°C, however, favor the growth of populations of this species. At 30°C, the spider's development to adulthood can take as little as seven days.
Other factors influencing the spread of spider mites are: the variety of cannabis cultivated and the age of the plant.
Spiders have a high reproduction rate under environmental conditions favorable for cultivation. The number of eggs a female lays can vary from dozens to hundreds.
They usually start their colonies in the lower areas of cannabis plants, and will colonize the plant upwards if action is not taken immediately.
Red spider mites spread from one plant to another through contact and wind. Wind can carry numerous mites from one plant to another and even from one area to another. Transmission via clothing and domestic animals, such as dogs and cats, is also very common.
Red Spider Video
When growing and environmental conditions are unfavorable, fertilized female spiders may hide among the equipment, stones, walls, etc. During this period they do not feed and remain dormant until conditions improve. For this reason, it is common for the infestation to reappear in the next crop after a previous one has been affected by spider mites.
The feeding of the larvae, nymphs, and adults, which rupture the tissues of the cannabis plant with their stylet and suck out the cellular contents, is the main damage caused by spider mites. The plant's metabolism is disrupted, resulting in chlorosis in the affected leaves, stunted growth, and necrosis and death of the affected tissues due to the effects of heat and/or agrochemicals.
Red spider mites produce silk threads and live in colonies among them. The webs formed by these threads create a microclimate favorable to their development by retaining the plant's transpiration moisture, allowing them to thrive in very low humidity. Furthermore, these webs constitute a true physical barrier, impermeable to water, agrochemicals, and also to predatory or parasitic insects.
The first visible symptoms on cannabis plants are tiny yellow spots on the upper surface of the leaves, resulting from the feeding and sucking action of these mites. These spots may be clustered in the center of the leaflets or more scattered across the leaf.
It is not common to find individuals on the upper surface; they usually take refuge on the underside of the leaves to avoid direct light and feel protected.
Control method
Preventing spider mites in outdoor crops is possible by carrying out appropriate practices such as eliminating nearby sources of infestation, encouraging the development of beneficial insects, and applying sulfur treatments to the crop during periods of high heat. These preventative sulfur treatments can protect the crop from spider mites during growth, pre-flowering, and even the beginning of flowering, but it should be noted that treatments on the flower buds are not recommended during the later stages of flowering.
The most effective technique for controlling spider mites is through biological control, specifically the application of predatory mites. Phitoseilus persimilis It allows crops to be kept free of red spider mite pests.