Although the spider mite ( Tetranychus urticae ) is probably one of the best known mites, there are related species that affect specific crops. This is the case of the so-called yellow spider , represented by the species Eotetranychus carpini and which mainly affects vine cultivation.
This mite from the tetranychid family is currently present in almost all wine-growing areas in Spain , especially in environments with drier summers and higher temperatures, an environment conducive to the development of this pest.
The objective of this article is to help in its identification and to give some advice on the prevention and control of the pest when it appears above the threshold of damage to the crop.
YELLOW SPIDER ( EOTETRANYCHUS CARPINI ) IDENTIFICATION
Mite attacks usually begin in spring , when temperatures rise and humidity progressively drops. Under these conditions, the yellow spider begins to activate and the number of reproductions skyrockets.
These small yellow mites can be found in all areas with significant vine cultivation, except in very humid areas, such as those in Galicia.
We carry out the identification of the different stages of the plague as follows:
- Adult: oval-shaped body and 4 pairs of legs, 8 in total. We can differentiate between male and female, the female being slightly larger than the male. The length of adult individuals is 0.5 mm in length, so it is difficult to see them in motion, except with a magnifying glass.
- Eggs: spherical size 0.1 mm in diameter, almost translucent to the naked eye, and progressively evolve with more yellowish tones (even amber).
This summer activity pest spends the winter in a nymphal or even adult state, but protected from the cold in the bark of the vines, fallen leaves or in weeds. Before bud movement on the vine, the females begin their activity, even with a certain cold in the environment (from March or April, depending on the area).
Well into spring, the adults move to the newly sprouted vine leaves , starting in May, where they colonize all the shoots, especially those in the lower part, feeding on the sap produced by the vine and starting to multiply in a way. dizzying.
Depending on the weather, during spring and summer 10 to 15 generations can pass, soaring according to higher temperatures and lower humidity. The optimal conditions for its development are in the range of 30-35 ºC, up to 40 ºC, with a relative humidity of between 30-45%.
In this cycle, the female can lay between 50 and 90 eggs approximately, depending on the atmospheric conditions.
PERIOD OF ACTION OF THE PEST
Tetranychid mites, both spider mites ( Tetranychus urticae ) and yellow spider ( Eotetranychus carpini ), need hot weather conditions and dry seasons. They do not support cold weather and high relative humidity, reducing the number of generations produced.
For this reason, the highest incidence of yellow spider occurs between the months of May to August , practically the entire period from sprouting to almost the final veraison of the grape.
It is in May and June (depending on the cold in the area), when the female generally colonizes the lower part of the plant, progressively advancing and causing damage to the entire aerial mass of the vine. Multiplication and feeding usually take place on young leaves, since adults have an easier time extracting all the juice from the sap.
In the case of a very strong attack on a vine, with partial or total defoliation in September , it influences the future cycle of the yellow spider, since this prevents new generations from being produced.
Read more: control mechanisms of vine phylloxera
Initial symptoms of yellow spider. Left, white grape variety and right, red variety
DAMAGE CAUSED TO THE PLANT
The damage caused by the yellow spider in the vineyard is usually related to the general weakening of the crop by sucking the sap . Attacks by adults cause deformation of the leaves, change in color and, in advanced attacks, premature defoliation of the plant.
Damage caused at the beginning of the vegetation
The first attacks, generally on the lower leaves, cause deformation of the leaves , reduction in the size of the clusters and shortening of the internodes. The affected leaves change their hue to more yellowish reddish and coppery colors, so the affected strains are easy to identify.
The most affected leaves usually coincide with the basal ones, slowly ascending as the pest progresses.
Damage caused in full production (summer)
As the plague progresses, temperatures rise and relative humidity decreases, yellow spider populations tend to increase. Much of the foliar mass of the vine changes color, with very striking red and chlorotic tones , but preserving the veins with their original green.
In cases where the leaves are very weakened by the suction of sap, the leaf tends to fall prematurely.
Loss of production and quality of the grape
The general weakening of the vine and the lack of energy causes a drastic drop in production , generating alterations in the quality of the grape. In addition, the premature fall of the leaves means that the accumulation of reserves for the following season is also considerably reduced, which can affect future production and the alcoholic degree produced.
In general, it is not so common for fruit damage to occur, although necrotic dots may appear in isolated cases and with a high population of yellow spider.