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Conyza in Olive Growing

José María Urbano Fuentes-Guerra

Higher Technical School of Agricultural Engineering. University of Seville

Conyza in Olive Growing
José María Urbano Fuentes-Guerra
Higher Technical School of Agricultural Engineering. University of Seville
Efforts to clear weeds have traditionally involved tilling, but tillage of olive trees involves significant environmental and economic costs. However, tilling has not only failed to remove weeds but has selected for particularly adaptive weeds.
The emergence of herbicides, particularly simazine (registered in the US in 1957), was a revolution.

Conyza in Olive Growing
José María Urbano Fuentes-Guerra
Higher Technical School of Agricultural Engineering. University of Seville
Efforts to clear weeds have traditionally involved tilling, but tillage of olive trees involves significant environmental and economic costs. However, tilling has not only failed to remove weeds but has selected for particularly adaptive weeds.
The emergence of herbicides, particularly simazine (registered in the US in 1957), was a revolution. One application before the first autumn rains was enough to keep the soil clear of weeds throughout the crop year, providing an effective, cheap and simple procedure. Chemical control has made it possible to reduce the frequency and intensity of tillage, but the types of weeds affecting olive crops have gradually changed over time, in terms of species (flora inversion) or biotypes (resistance). The species that have developed resistance to simazine are Conyza bonariensis and C. canadensis (1987)
Conclusion 1: Weeds adapt to a farmer’s predictable behaviour.
The response to apparent lack of effectiveness tends to be to increase the dose and/or to supplement weed control with a mix of herbicides and with tillage. However, tilling treated soils with residual herbicides encourages erosion and pollution of superficial aquifers, since the herbicide sticks to eroded soil and is carried with it. Simazine was banned in 2003 but many olive growers remain attached to the idea that the ground under their trees could be perfectly free of noncrop plants. 
With the banning of simazine, glyphosate has been used increasingly as a broad-spectrum herbicide. 2004 saw the appearance of the first Spanish glyphosate-resistant biotype of C. bonariensis, which was followed by C. canadensis (2006) and C. sumatrensis (2009).
Conclusion 2: The continued application of the same herbicide allows weeds to adapt.
In a survey conducted in 2014, Conyza appears as the most worrying weed pest, because it is difficult to keep in check with herbicides. Weed management requires an integrated approach, but this is even more necessary in the case of Conyza species. It is essential to rotate active ingredients with different modes of action, to optimise application times and rates, and use non-chemical methods: mechanical (harrows), cultural (plant cover), etc.
Conclusion 3: The problem of olive-grove Conyza requires integrated weed management approaches.

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In accordance with the Organic Law on the Protection of Personal Data 15/1999, of 13 December, Promotora de Exportaciones Catalanas SA (hereinafter PRODECA), whose address is Gran Via de les Corts Catalanes, 620, principal, 08007 Barcelona, with tax reg. no. NIF A58241316, declares that the images contained on the website www.smartfruitcongress.cat are included in a file belonging to PRODECA. The purpose of this file is the promotion, via its website, of the activities conducted by PRODECA – SmartfFruit IPM International Congress.

PRODECA guarantees that you may, at any time, exercise your right to access, rectify, cancel or oppose by writing to the aforesaid postal address, using the reference "PROTECCIÓN DE DATOS - SMARTFRUIT", or to the email address smartfruitcongress@smartfruitcongress.cat.

Specifically, to correctly exercise these rights you must clearly provide the following items in that communication:
- Name, surname(s) and photocopy of National Identity Document or Passport.
- Statement of the purpose of the request.
- Address for notification purposes.
PRODECA also declares that it reserves the right to delete from its website any content that it considers violates current and applicable legislation.

D’acord amb l’article 17.1 de la Llei 19/2014, la ©Generalitat de Catalunya permet la reutilització dels continguts i de les dades sempre que se'n citi la font i la data d'actualització i que no es desnaturalitzi la informació (article 8 de la Llei 37/2007) i també que no es contradigui amb una llicència específica.