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Yellow spider identification and control

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.

HOW TO CONTROL THE YELLOW SPIDER

This part is essential, having previously identified that it is a yellow spider attack, it is time to delve into the authorized treatments for its control. The pest prevention strategies involve preventing the vine strains from generating a very dense foliar mass that facilitates the work of the mite.

Read more:  guide and schedule of vineyard treatments .

PREVENTION OF ATTACKS AND CULTURAL MEASURES

Weed control

The weeds near the vines can be a refuge for adults from September and at the beginning of the activity in the future season, before spring. Although, from an environmental point of view, it is not advisable to eliminate 100% of the cover of the adventitious grasses to improve the structure of the soil, plow passes and grass clippings are recommended to avoid the proliferation of the yellow spider.

Pruning and maintenance of the tree structure

The pruning of the vineyard has great benefits from several points of view. On the one hand, we maintain control of the aerial part of the vineyard and, on the other, we avoid a high density of leaves that favors the proliferation of different pests.

The stripping and stripping improves the ventilation of the crop. Although this advantage is very attractive against fungi and bacteria, it is also attractive for pests, since it allows greater coverage and penetration of insecticides and acaricides.

SYMPTOMS OF THE YELLOW SPIDER

When interpreting whether or not we should carry out control treatments against the yellow spider, the following classification is made according to the incidence of the plague:

  • Type 0: undamaged vineyard.
  • Type 1: vine with localized damage in the lower part of the vine, below the formation of the bunches.
  • Type 2: vine with damage to the entire foliar mass of the strain, including the vegetative parts above the bunches.

Read more:  the alarming tinder of the vine

WHEN TO PERFORM ACARICIDAL TREATMENTS

Flowering

The control treatments against the yellow spider start from flowering, when we have detected damage to the crop in approximately 5% of the strains (symptoms type 1 and type 2).

Start of summer

In cases with later warm temperatures, the incidence will be reviewed from June and July, with 25% of Type 1 strains affected and 5% of Type 2 strains.

CHEMICAL CONTROL OF YELLOW SPIDER

Through the following link you will find the phytosanitary products authorized for the control of the yellow spider.

Read more:  authorized products against yellow spider .

ECOLOGICAL CONTROL

In organic farming, prevention is the main mechanism to control different diseases and pests. Against fungi, copper is one of the best alternatives, and in the case of the yellow spider, sulfur is an effective product if we use it in advance before the pest evolves unfavorably.

A maximum of 20 to 30 kg per hectare is usually applied, with up to 3 applications, avoiding its contribution in the warmest months of the campaign to avoid possible burns.

Cover photo: photography rights attributed to Julio Prieto . Other photographs: General Subdirectorate for Primary Production Health and Plant Protection and Plant Health Services of the Autonomous Communities.

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