Gardening

Red spider mite


Question: Red spider mite


What to do for this boring red spider? Are there any effective "natural" remedies?
In Turin, on my south-facing terrace, various plants suffer from this problem. Is there someone who can give me some suggestions? Thanks. (Giusy)

Answer: Red spider mite


Dear Marco,
Thank you for contacting us about the problem with your plants through the Expert's column
The red spider mite Tetranychus urticale belonging to the Tentranichidi family. The main damages produced on the vegetation following the attack of these lithophagous, manifest themselves with yellow-grayish leaf discolorations and with the appearance of residual cobwebs found on the lower page; the infested leaves can fall or necrotize in advance and the flowers can also be damaged.
The presence of red spider mite due to its feeding system (sucks the sap), can actually affect the flowering and depress the development of the plants of its terrace. We are not aware of effective "natural" remedies on this very boring plant pest.
With best regards

Description Red spider mite



































Family and gender
Mites, Tetranychus, urticae
Common names Red spider mite, red mite, red spider of greenhouses
Plants affected Numerous, up to 1000 different species
Damage Yellowing, loss of vitality, death, low productivity
Symptoms Yellowing, appearance of rust-colored spots, “dry” looking leaves, very small dots on the lower side, very light cobwebs (if the condition is very serious)
Triggering factors Dry heat, sunny exposure, low humidity
Period of appearance Late spring
Remedies Increased humidity, exposure change, vaporization, acaricides

The males are peripherormi with wide legs and more round females. Colors can range from orange red to bright yellow with red eyes. When they are not yet adults they have a similar shape to the mature one, but they are only equipped with 3 pairs of legs instead of four and the coloring is clearer. The egg is round, shiny and transparent. As it evolves, the color turns more and more to orange.

Red spider life cycle



Populations begin to increase in number in the early spring. During the hot season they are able to complete a generation within a week. Times are longer when temperatures are lower. In areas where winters are mild (Southern Italy, tropical areas) generations can follow each other throughout the year, even if in the cold season they will be slowed down. In colder regions they can spend the winter both in the form of adult and under that of egg.
At our latitudes you can have at most 6-8 generations per year. The situation changes considerably if we talk about plants grown in greenhouses.

Symptoms and damage from red spider mites



leaves: there is a clear discoloration due to the bites of the parasite buccal apparatus. Generally this is located near the central veins and it is precisely there that the first symptoms appear. The discolorations take on a yellow-rusty appearance and the leaf takes on a dry and weakened appearance. If no action is taken then the fall occurs, especially in the presence of dry wind.
In some types of citrus fruit there is the appearance of orange bubbles.
If no action is taken in time (and the climatic conditions are favorable), there will also be the appearance of small cobwebs: it is in a very advanced phase of the infestation.
fruits: in the affected areas dark stains appear that give the product a dirty appearance.
To recognize from the first symptoms the condition, it is necessary to observe, possibly with a magnifying glass, the back of the leaves. The problem is if you notice very small dots (barely visible to the naked eye) that are red or even dark brown.

Red spider mite: Red spider mite fighting




The strategy to be applied must be commensurate with our climatic conditions. In some areas (for example Northern Italy), the spider makes its appearance in the summer and manages to complete only a few generations. In this case the use of acaricides is not indicated.
To weaken the aggressiveness of the mite it may even be sufficient to move the plant (which is almost always in a pot) in a more shady area and vaporize the foliage several times during the day. It may also be useful to repeatedly wet the floor around or place a saucer filled with expanded clay and water at the base. It is also important to lift the container off the ground so that it does not come into direct contact with the overheated floor: it would cause the substrate temperature to rise and the mite to have better life conditions.
A further help can come from the use of mulch (pine bark) that helps the substrate to stay fresh and moist.
While the situation almost never becomes severe in gardens, it can instead become so on very sunny balconies and terraces (and clearly in the greenhouses and in the Center-South).
In this case it may become essential to intervene with specific acaricidal products. The period in which the spider is most sensitive runs from June to August. However, we would like to point out that the products on the market for hobby use are not very effective and unfortunately the animal quickly develops resistance. We therefore avoid using them excessively. Usually for domestic use only one treatment per year is recommended.
We pay particular attention to the choice of the product (always acaricide and not insecticide!): It must combine different active molecules against all stages of development, from egg to adult and that has a translaminar or cytotropic action.
For the prevention it can also be useful, during the winter, the distribution of white oil (which acts by asphyxiation) on the whole trunk of the plant (perhaps mixed with an ovocide).
The natural enemies are other mites (Neoseiulus californicus y Phytoseiulus persimilis) and some ladybirds. At the domestic level it is difficult to obtain good results, in greenhouses instead they can be useful at least to limit the impact.