Red spider, a big threat to cropsIt is considered a pest problem for vegetable crops (field and protected areas),

orchards (especially peach/Nectarine trees) or vine and in some cases for the

cultivation of soybeans. Lately appeared to extend this information harmful to other

agricultural crops such as maize and sunflowers

Adult is a small mite with dimensions less than 0,5 mm.

The Male has piriform body, a bit smaller than the females, the color being

generally greenish-yellow.

The determining factor for the attack with high intensity is drought. Even in the

case of moderate temperatures, if is drought, the attack in the field will have a high

intensity. If the rains occur during this period then we will assist at the reducing the

attack.

Adults and nymphs are found on the underside of the leaves. They feed by

puncturing and sucking the cell juice from the leaves. Attacked leaves fade and acquire

a characteristic mosaic aspect. Later they dry and fall. Photosynthetic capacityof the

attacked leaf decreases, there is a loss of water from damaged tissues, the

development stagnates and the production decreases.

On corn crop, red spider can be found distributed evenly over the whole plant.

The attacked leaves turn yellow. In some cases the leaves become white to yelowish.

Symptoms usually do not appear all over the surface of the leaves, but only on some

portions. If the attack coincides with a period of increased drought, maize plants dry

faster, and the production quantity losses can be high.

Chemical control

Here are several aspects worth mentioned. There are numerous references in

the literature about the resistance of this species to acaricides. The main cause is due

to the large capacity of multiplication of daunatorului, as well as the short duration of a

generation. Moreover, common red spider is considered one of the species that has

developed a resistance to several chemical plants over time, becoming a harmful

problem in many areas of the world. Also, climate change can influence positively the

development of mites. For example, in our country, long and dry autumns, can have the

effect of increasing the number of generations in the field and as a result increasing the

biological reserve. Today, in our country are relatively low amount approved of active

substances for control of this mite fitofag. For all crops (including vegetables, orchards,

vineyards, etc.), plant-protection products on the Codex in 2013 are mentioned the

following active substances: fenbutatinoxyde, fenpiroximat, hexithiazox, spirodiclofen

and pyridaben, clofentezine. In total, six active substances, a number quite small

relative to the large number of home-grown plants.

Surveys in the field

The soybean crop, before applying a treatment in vegetation surveys to be

carried out in the field to see if it has reached the threshold of economic daunare (PED).

It is 5-6 mites (adults and/or nymphs)/planta. The leaves from the bottom/middle/upper

part of the plant are examined with a magnifying glasses (x 10). To establish the

presence or absence of adults, eggs or nymphs. The attack is observed with ease after

this a fabric matasoase lax, which are circulating many mites. Another simple method of

estimation of the density is shaking the leaves over a white sheets. Adults recognize

with ease while moving on the white sheet. In the literature it mentions another method

of estimating daunatorului density depending on the percentage of leaves with

symptoms of attack. When the leaves are attacked in a percentage of 10-15% is

recommended to perform the treatments. In this case, however, should be

disambiguated as well with the attack caused symptoms caused by other stress

impacts, such as secetea. The maize culture does not yet exist a standardized method

planned for our country regarding the time of treatment. In the specialized literature in

the USA is mentioned as if they are still active colonies of mites on a third of the leaves

on a plant at 50% of the total monitored or when plants 15-20% of the surface of the leaf

is covered with the characteristic Cobweb warrants treatment in vegetation with an

acaricide. In Romania the situation of attack than mites in corn is not yet commonly

intâlnita, although there are signals from the farmers on this fact. For this reason, nor

are they approved acaricides for corn. Soybean culture are approved for the following

products: SC Reminder (0.5 l/ha), 5 SC Ortus (0.5 l/ha), Nissorun 10 WP (0,4 kg/ha),

Envidor SC 240 (0.3 l/ha). In agricultural practice is performed only in vegetation

treatment per year to soy, but I have watched carefully the evolution of the PED

(economic threshold of daunare). It is important to note that at present, the laboratory of

plant protection INCDA Fundulea, are tested for omologarii and other products to

combat the red spider in vegetation.