FARMER FOCUS: A growing glyphosate resistance problem

Resistance to glyphosate in several weeds is creating quite a headache for Argentinian farmers such as myself.

In some parts of the fields I am working, the weed amaranthus quitensis (ataco) seems to be acquiring resistance to this herbicide.

This is on top of the resistant weeds that are already present in plots of soybeans and corn, such as some Johnsongrass species, sporobolus, gomphrena perennis, and the well-known weed conyza bonaerensis (flaxleaf fleabane).

Studies by professional and official institutes showed that some of these amaranthus quitensis plants survived treatments of up to 30 litres/ha of glyphosate.

One of the features is that each plant produces many seeds and the primary means of propagation is the combine. The seed is very small and gets trapped in any orifice of the machine. In our region it is very common to use contractors for harvest operations, and this is an important factor in the spread from one field to another.

In general, we can say this is a large plant that competes with the crops and, therefore, generates significant economic losses. Some technical experts speak of losses up to $50/ha (£30).

Some of the measures being taken to tackle weeds include avoiding harvesting areas where their presence is high, or performing a thorough cleaning of the combine before entering the plot for harvest. Another alternative is the use of chemical herbicides pre-emergence based on triazines. A final option is try to use the hoe to cut them, if their presence is obviously not too extensive.

The option to remove soil is not recommended, since this weed was present during the years in which the plough was used, and the no-till system had not yet been introduced. This is in contrast to conyza bonaerensis, where control would be helped by removing soil and sticking with the no-till approach.

In conclusion, we must deploy measures that favour the crop, not the weeds. This includes reducing the distance between rows to shade gaps faster and prevent further weed establishment.

Federico Rolle farms 2,250ha of rented arable land in the Pampa area of Argentina. He grows soya beans, sorghum, maize and wheat using no-till techniques and GM crops. He has a part-time role helping Brown & Co in the region

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