The weed management is integrating when concepts and practices of chemical, biological, mechanical and cultural origin are considered, it was the first idea expressed by the Doctor of Agricultural Sciences Eduardo Cortes, private advisor and professor of biology, of the Faculty of Agricultural Sciences of Córdoba. His dissertation took place at the Maíz más Sorgo 2021 colloquium, organized by the Todo Agro group and the consultant Pablo Adreani.
“The first aspect to take into account for a successful weed control is the monitoring, in order to know the weeds that we have in the lot. That is, if they are annual, perennial, broad-leaved or narrow, if they sprout sooner or later, to design a management of them. The monitoring is before treatment and also after, because the appearance of resistance and growth of tolerances have generated problems in the controls ”said the specialist.
“Before, an application of glyphosate plus 2.4 D was made with some sulfunylurea or atrazine and then it was sown because everything was controlled without problems. But at this time it is different, since there may be problems in relation to the efficacy of treatments and therefore it is necessary to carry out controls “, explained Corté.” And it is necessary keep track of weeds present ”he stated.
Doctor in Agricultural Sciences, Eduardo Cortés, the first step to be successful in weed control is monitoring before and after any application.
In the Córdoba region there is a ranking of weed abundance that is like this: in fourth grade we record Conyza, Echinocloa, Amaranthus, (with 50 and 75% coverage), after second grade this Aleppo sorghum, (with coverage of 5 to 25%), and in the first degree, Parietaria, Commelina, Digitaria and Eleusine (with dispersed individuals or coverage less than 5%). “This ranking varies by area, for example, further south Eleusine will go to second or third grade. It is important that, for the work area, the weed ranking resulting from monitoring, “he said.
Through monitoring, the seed bank can also be known. And if we have a strong presence of a certain weed, we know that we will have a lot of seed of it, and precisely in that seed bank is where we must work. And the handling should be aimed at lower the seed bank off the ground.
Aleppo sorghum, red yuyo and ryegrass, capable of surviving two or more herbicides with different modes of action. Better is to mix active products
“That bank is the weed evolutionary memory, which changes depending on the climatic conditions, the amount of cover and the management of different herbicides at different times. Know when the weeds are born it can help in management, “said the specialist.
On the other hand, he stressed that it is important to remember that hedge negatively impacts weeds that have generated the main problems in recent years, because they are seeds of small size.
Therefore, they germinate from the first two centimeters from the ground. And more precisely, the 70 to 80% of them germinate from the first centimeter in depth of the soil.
“In a bare soil the germination of the seeds will be total, but if it were covered with the increased amount of stubble possible, this will impact on the temperature, the arrival of light, and the thermal amplitude, which is the difference between the maximum and minimum temperatures, “he said.
In this sense, the obstruction of these factors generates the seed dormancy that may happen for the following year. In addition, this coverage will enhance effectiveness of pre-emergent, because it will work on fewer germinated weeds.
“Thus we see that, for the management of weeds in corn or sorghum, the It is important to have a well-established crop with good growth, “he said.
Conyza (Black Branch) one of the most widespread weeds.
For which, the sowing date, row spacing, planting density, well done fertilization, plant architecture, tolerance to different herbicides, and all this will help the best and fastest development of the crop.
Finally, you can consider the mechanical handling as one more tool, which we must take into consideration when we have perennial weeds what are the ones they have secondary reproductive organs such as tubers, rhizomes, in which we impact with this mechanical handling.
Instead, annual weeds They are the ones that have their seeds in the soil profile, and with mechanical handling we can bury some of them, but we can also unearth others that will suddenly appear and that we did not expect.
Herbicides for corn and sorghum
“It is necessary to define what main weeds we have, among which we can mention Amaranthus (red weed). Generally, in the areas I visit it is the main one, and for its control there are a series of products that can be used more for corn, but not so much for sorghum, “said the specialist.
To conventional sorghum, you can use some triazines and some chloroacetamides, and in sorghum IMI they can be used imidazolinones.
“It is necessary to determine the primary and secondary weed, because currently in each batch, seven or eight weeds coexist different, and although one is the main one and two or three are the secondary ones, and the idea is to choose some product for the main one and also another for the secondary one, “he said.
At this point, he continued, the imidazolinones in sorghum, which give us the option of using them alone or in mixtures, and in pre or post emergency, and that are dedicated to the management of grasses. In conventional sorghums, we have mixtures of triazines and coloroacetamiandes such as acetochlor.
It is convenient to rotate and mix assets between early and late sowings, in order to reduce the possibility of the appearance of resistance “, advised the specialist.
Red weed infection.
It is also important, he noted, to take into account that these assets are effective hup to 45 days after application. And furthermore, we must ensure that the crop is clean for 25 to 30 days from sowing, especially sorghum, which is the one that has the least herbicides for its management.
Better are the active mixes
The key point of pre-emergent is to mix different assets, in order to avoid weed escapes. On the other hand, do not forget that eon bare soil there will be more births than with stubble and that the greater the amount of stubble, the more abundant rainfall for the incorporation of herbicides.
“Nor should we forget that herbicides, to be effective, must pass into the soil solution and for this they need to be incorporated with a rain. In other words, “we cannot achieve good controls if we do not have rainfall,” said Cortés.
And moving on to the emerging post, in conventional sorghum we only have triazines like atrazine. Some hormones are also available, which I do not recommend because it can generate phytotoxicity. This lack of tools is what makes it convenient for all conventional sorghum to start clean, said the engineer.
In the case of sorghum IMI a battery of imidazolinones is available that offers good control over grasses. Although not about red yuyo that usually has resistance, but can be mixed with triazine and achieve better control.
In the case of post-emergent corn, we have glyphosate, glufosinate for resistant and tolerant crops respectively. Corns with specific technology are also available to use hormones or graminicides.
But the herbicides most used in corn are HPPD That They can be used with any hybrid, and atrazine must always be added, for example, which makes the controls much more effective. The same if you add ammonium sulfate, or some oil.
And if glyphosate is added, when possible, the control is very good, mainly in broadleaf weeds such as Amaranthus. In grasses the controls are good, but as long as the weed is small.
These products are like the silver bullet to rescue a lot, that is to say in extreme opportunities, so as not to increase the costs of the crop. Also, remember that if we have weeds and we must use these herbicides, it is because we are not handling the batches well. There may be a year or a specific case but it should not be generalized.
Finally, it is to take into account when using the post – pop-ups, the quality of application that is a determining point in the success of weed control“Emphasized Cortés to finish.