The search for optimizing the operational capacity of sprayers has encouraged the application of increasingly complex solutions, notably due to the use of mixtures containing several agricultural pesticides, adjuvants and foliar fertilizers at the same time.
Although the result of this practice is questionable in some cases, when the mixture is made without apparent agronomic criteria, it is clear that its use is increasingly frequent.
An aggravating factor for this process is the concomitant reduction in the application rate (Figure 1), which makes mixing several products in a reduced amount of water a very complex technical challenge (Chechetto et al, 2014; Carvalho et al, 2017).
There is also a growing demand for tank mixes to correctly manage plant resistance to pesticides. In this case, the issue of herbicides is of particular interest, as the number of cases of resistance or tolerance of weed species to different modes of action has been increasing year after year, requiring the use of strategies for applying mixtures that can provide longevity and sustainability to chemical weed control.
Therefore, it is necessary to understand the factors that interfere in tank mixtures containing glyphosate and 2,4-D-based herbicides, with a view to the physical-chemical compatibility of the mixtures. We tested these herbicides by varying the concentration (through the application rate), the commercial brand and the mixing order.
The research was conducted by AgroEfetiva in partnership with the Faculty of Agricultural Sciences, Unesp, in Botucatu (SP). Initially, an experiment was carried out with two commercial products based on glyphosate WG, described in Table 1.
Two commercial brands of glyphosate WG were analyzed with the herbicide 2,4-D (dimethylamine salt of (2,4-dichlorophenoxy) aceticacid), 806g/L (670g.ea/L), at a dose of 3,5L/ha.
The treatments consisted of two sequences of mixing the products (for example, first glyphosate and then 2,4-D, or vice versa) and different application rates, 40L/ha, 80L/ha, 180L/ha and 250L/ha, thus offering different concentrations of the products in the sprays.
In a second step, a foliar fertilizer (homogeneous suspension; 2% nitrogen, 3% potassium oxide; and 1% manganese) was added to the broths containing glyphosate, at a dose of 0,4 L/ha, without mixing with 2,4-D.
In order to preserve the practical agronomic aspect of the proposed treatments, all glyphosate-based products were dosed in the sprays considering a basic recommendation of 1.800gea/ha of glyphosate.
In this way, the dose, in liters of commercial product per hectare for each herbicide, was adjusted to proceed with the mixture so that all treatments offered the same control potential (based on a standard dose of 1.800gea/ha).
All treatments started with an initial application rate of 40 liters per hectare, and this value was increased until a change in behavior was perceived in case of compatibility problems in the mixture. For WG products, the maximum application rate used (250 L/ha) represents the highest rate recommended in the package insert for these products.
The compatibility assessment was carried out based on the methodology described in ASTM E1518 – 05 (2012). The mixture is considered compatible when, at the end of the agitation process, it is homogeneous and no residues are found on the sieve or in the container where it is stored.
It was possible to observe that in all mixtures, between glyphosates WG and 2,4-D, below 180 L/ha, there were compatibility problems for any herbicide tested and in any mixing order.
Table 2 presents the compatibility data relating to the evaluations for the two glyphosate-based herbicides WG (ammonium salt), in a mixture with 2,4-D and also in a mixture with the foliar fertilizer.
Only in the tank mixture with 180 L/ha was it possible to observe differences between the pesticides for mixture compatibility. Whenever 2,4-D was added first in the mixture, up to 180 L/ha, there were problems with mixture compatibility, regardless of the commercial brand of glyphosate.
When the mixing order was performed with glyphosate WG added first to the mixture, the results were different for the two commercial brands tested. In this case, there were compatibility problems for the gliwg1 brand, while no compatibility problems were observed for the gliwg2 brand. For the maximum application rate recommended in the package insert for the WG formulations (250 L/ha), there were no compatibility problems with the method analyzed for the two commercial products, even when the mixing order varied.
The results show that as the solutions became increasingly diluted (corresponding to the highest application rate), the compatibility problems disappeared. However, in this process it was possible to clearly observe a difference in behavior between the commercial brands. While the mixture of the herbicide gliwg1 still resulted in compatibility problems at the dilution of 180 L/ha, the mixture of the herbicide gliwg2 already resulted in a compatible solution at this dilution.
Therefore, any tank mixing recommendations for these two herbicides would need to be differentiated between commercial brands. These differences in behavior between commercial products are expected in practice, due to the qualitative and quantitative variations of the components of each formulation (the inerts), which may interact with each other in the spray and may or may not cause compatibility problems, depending on their concentrations.
Mixtures with gliwg1 and gliwg2 + foliar fertilizer did not result in compatibility problems for any application rate and in any mixing order evaluated.
The treatments with compatibility problems tested in this research, with these doses, at these application rates and for these products, require attention when used in mixtures. From this scenario, it is possible to conclude three main parameters:
* By Rodolfo Glauber Chechetto; Fernando Kassis Carvalho; Alisson Augusto Barbieri Mota (AgroEffective); Ulisses Rocha Antuniassi (FCA/Unesp)
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By Lucas de Arruda Viana, Fernando Ferreira Lima dos Santos, Guilherme de Moura Araújo, Rodrigo Nogueira Martins, Jorge Tadeu Fim Rosas, Samira Luns Hatum de Almeida and Laércio Zambolim, from UFV
