Panonychus ulmi
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| Panonychus ulmi Henry Kock |
Panonychus ulmi, better known as Red little spider of the fertile ones and the grapevine, is a phytophagous of the fruit plants and the grapevine where alive on the pages inferior and superior of the leaves and on the buds. The females appear of small dimensions, 0.5 mm of length around; they are of red pave color with whitish tubercoli on the back, which correspond to the insertion point of the dorsal bristles. The tubercolis are organs that allow the identification of these ragnettis from others them similar, what the Tetranychus urticae. The males are smaller than the females and of clearer color; the young little spiders appear, instead, of color yellow-orange tree. The winter eggs they is able well to identify for their red color I live, while those spring-summer are yellow-orange tree as the larvas. The damage through that this Little spider provokes of the punctures, is very characteristic on the buds but above all on the leaves, that pardon easily brightness of the superior page, they decolor them and assume a bronzy coloration; subsequently they detach him from the plant and they desiccate. Under a careful examination, always in presence of the illness caused by the Little spider, the foil leaf door, besides, of the necrosis and punctuated decolorations and, then anchor, a lot of mobile forms and their metabolic residues are visible (excrements and esuvie), in the form of powder "white-greyish", above all on the inferior page. They can finally be noticed some small and weary plots sericee, whitish, shed on the two leaf pages to confirmation of the colonization from the acaro. On the productions the damage is the direct consequence of the serious filloptosis that they are verified in correspondence of the acaro. The Panonychus winter as egg on the woody organs and it completes 7-8 generations a year.
[edit] Struggle
The struggle against the Panonychus ulmi effects him doing first some fundamental considerations, that are also worth for the other acaris:
1) the Little spider is become a very serious problem, particularly when starts to fight it;
2) before effecting the relative treatments it is essential to appraise the consistence of the biocoenosis, particularly:
- it is had to verify the presence of his effective natural inspectors, among which: the Coccinellidis Stethorus punctillum, the Antocoridis of the kind Orius, the predatory Acaris Amblysesius andersonii and Kampimodromus aberrans;
- it is had to verify the presence of the Red little spider and to compare his population with the raiders, to determine the thresholds of intervention.
On the fertile ones the threshold of intervention is equal to around the 50-90% of leaves infested by the mobile forms of the acarus; it is had to consider however that it doesn't need to intervene in presence of a congruous relationship acaris natural phytophagous/antagonist. Among these it dresses again particular a lot of importance the Stethorus punctillum, that can be enough for every 2-3 leaves one of it, to dissuade the intervention. For some varieties of however sensitive to the Bruson, induced also from the presence of acaris, the threshold corresponds to the first infestation. On the grapevine the threshold to be considered is:
- equal to around 60-70% of infested leaves, in spring;
- equal to around 30-45% of infested leaves, in the summer.
The chemical products to be used, for specific interventions, in case of overcoming of the threshold of intervention are:
- for the grapevine: Fenazaquin, Clofentezine, Tebufenpirad, Fenpyroximate, Pyridaben, Dicofol, Fenbutatin-oxide (neanicide), Exitazox;
- for the apple tree: Fenpyroximate, Tebufenpirad, Pyridaben, Azocyclotin, eventually mixed with Exitazox (active also on eggs and citotropic) or with Clofentezine (eggcide), for the contemporary presence of different stadiums of development;
- for the however: is recommends Exitazox, Tubufenpirad, Fenazaquin, Fenbutatin-oxide, Fenpyroximate, Pyridaben, Clofentezine;
- for the Drupacees: Dicofol, Fenpyroximate, Pyridaben, Exitazox, Tebufenpirad, Fenazaquin, Clofentezine.
The use of Brominepropilate is recommended, also recorded on the grapevine and Peach tree, active on eggs and mobile forms. On however, apple tree, grapevine and citrus fruit it is employable the insecticide-acaricidal Flufenoxuron, chitino-inhibiting active translaminare on eggs and juvenile stadiums. For whatever case, with the purpose to prevent serious problems owed by the presence of the ragnettis, it is oppurtuno to perform a suitable struggle against the other fitofagis avoiding the use of insecticides to ample ghost of action, ex. Piretroidis that "they sterilize the biocoenosis" killing important inspectors of the acaris, what the predatory Hemipterans, Gall midges and others. Finally it is opportune to remember that it is had to resort only to the acaricidal interventions in case of overcoming of the infestation, using selective products (ex. Clofentezine) that safeguards the useful entomofauna as the Acaris Fitoseidis and the Stigmeidis, good assistants against the litte spiders.
