Conyza bonariensis – Yerba butcher
Common name: Yerba butcher (Uruguay), Black branch (Argentina).
Scientific name: Conyza sp., Conyza bonariensis (It is most common in Uruguay), Conyza canadensis, Conyza sumatrensis.
Photo 1 – Conyza bonariensis in three different stages
Life habit: invernal (flowers in spring-summer).
Morphology: has grayish-green leaves, densely hairy. Semi-woody stem, cylindrical, with longitudinal stripes. height ranging from 0.2 to 2 meters.
Dispersion: It reproduces by seed. It is a very aggressive weed because it has a high seed production (up to 200 thousand in a plant) very small which are dispersed by the wind and can fly up to 2500 meters.
Presents very well adapted to direct seeding as it needs light to germinate. Supports periods of drought but is sensitive to competition. It is used medicinally as a diuretic, healing and descongentionante liver.
Problems and Control
La Conyza bonariensis has been transformed into a “difficult weed”, presenting a major cropping seasons in recent population growth.
In early stages there is a lot of efficient options for control, but as the plants increase in size becomes more expensive and difficult to achieve good levels of control while the results are more random.
In turn, in some countries (including Brazil), have reported glyphosate-resistant genotypes. Although not yet exist in Uruguay genotypes Conyza sp. resistant to glyphosate, we should treat it like one, making an integrated control of this weed in the system, with appropriate monitoring and, if resorting to chemical control, rotate the site of action of the active ingredients used.
Photo 2 – What we should not reach. Chacra soy problem butcher grass, Paysandú, December 2010.
The moment of greatest sensitivity to chemical control yerba butcher is when you have 2 to 5 sheets (up to 8 cm in diameter rosette). In these situations glyphosate normal or in combination with metsulfuron or 2,4-d is possible to achieve good control.
The adjuvant is recommended to use oil methyl ester.
Factors to consider
Sulfonilureas, imidazolinonas, triazolpirimidinas: have different but equally active site of action. It is important to rotate the site of action.
Sulfonilureas: Keep in mind that for planting sensitive crops to them prior to their application and depending on: dose rains, soil pH (chemical hydrolysis), history of herbicides, etc., should be about 90-120 days of waiting. In soybean, for example, may occur after phytotoxicity V6 because these substances accumulate in the Bt and the impact when the roots begin to explore.
2,4-d amina: when used with glyphosate should increase the volume of this (20%). It should be about 15-20 days waiting for planting sensitive crops, depending on humidity and temperature. At the same time, care must be taken when low volumes are used because they can precipitate.