Red Spider Mites
Tetranychus urticae
Red spider mites, Tetranychus urticae, are also known as Glasshouse spider mites or Two-spotted spider mites. They are a notorious pest of many species of glasshouse, indoor and garden plants, and if left untreated will cause serious damage and often death to young or tender plants.
Although Red spider mites are usually regarded as an insect pest they are actually related to spiders and have eight legs. They are about 0.4mm in length and normally browny green in colour with two dark green spots on their back. Their mouth parts are sharp and piercing and are used to penetrate plant cells to suck out the contents and feed on the sap. They initially begin feeding on the undersides of leaves which results in a characteristic mottling effect which appears on the upper surface of the leaves. It is at this point that conscientious gardeners should first notice the infestation and begin treating the affected plants. If left, the infestation will rapidly escalate to cover the entire plant as well as spread to surrounding plants.
Each adult female spider mite will live for up to 4 weeks and can lay up to five eggs a day. During this egg laying period, the spider mites continually produce silk webbing which forms a mat that covers the leaf surface and protects the infestation from rain and condensation. The webbing also makes it very difficult to effectively spray contact chemicals on to the mites. If left untreated, the webbing can completely cover the plant.
Eggs hatch in a few days into very active six-legged spider mite nymphs, which immediately start feeding. They soon shed their skins and from this point onwards have eight legs. From egg to adult can take between 7 and 20 days depending on temperature.
In general, Red spider mites prefer hot and dry conditions, but they can still be a problem within a cooler and wetter environment. In a heated greenhouse, there will be continuous generations, where as in a glasshouse that is not used during the winter months, spider mites can over-winter in a diapausal state, often in small groups in secluded locations.
It is therefore very important to thoroughly clean and wash out a greenhouse at the end of a growing season where spider mites have been a problem.
To control an infestation of spider mites, there are few chemical options available although these may not always be effective as many spider mite strains have developed resistance. Biological control however, is an effective alternative to chemicals where several predatory mites are available.
For early control or in colder conditions use ; Amblyseius andersoni in shaker bottles or in slow release predator bags which can be hung on the plants.
For large numbers in warm conditions use Phytosieulus persimilis - Just Spidermite Killer. This predator can be released onto the infested plant and left to catch and eat the Red spider mites. At temperatures of 18C and above, the predatory mite will reproduce at a greater rate than the spider mite and should soon overcome and control the infestation.
For Pest Control please view our Spider mite controls in the Pest Control section of the shop at www.just-green.com or
click on this link