Data and strategies for applying pesticides

Phytosanitary products, although they play an important role in the agricultural production system, have been the target of increasing concern on the part of different segments of society, due to their risk potential.

One of the ways to maximize application efficiency and minimize losses and contamination risks caused by agricultural pesticides can be the use of application techniques appropriate to each situation, in order to improve deposits on the target.

In addition to studying factors inherent to the weeds to be controlled, such as the species, development phase, architecture, density and form of reproduction, it is also essential to study factors inherent to the application, such as the product to be applied, the size and density of drops, losses to the ground and by drift, the spraying equipment, the volume of spray solution and the spray tips (Souza et al, 2007; Viana et al.

Currently, there are hydraulic spray tips on the market of various types and uses defined for different operating conditions. Another information of great importance for field conditions refers to the possibility of reducing the spray volumes currently used, as this would make it possible to increase the operational capacity and autonomy of the sprayers. This would reduce the cost of the application, however, it requires study on not compromising the efficiency of the application process.

Researchers from the Federal University of Uberlândia carried out tests to evaluate the desiccation of weeds, the deposition of spray mixture on the target, losses to the soil and drift caused by the application of herbicide, using different volumes of spray mixture and spray tips. pulverization.

HOW THE EVALUATION WAS DONE

In order to evaluate the herbicide application process in desiccating weeds, the active ingredient 2,4-D Amine (commercial product DMA 806 BR, at a concentration of 806g/L a.i.) was used at a dose of 1L/ha of commercial product, as recommended by the manufacturer, with the future installation of corn cultivation as a theoretical reference. The experiment consisted of six treatments as described in Table 1.

To apply the treatments, a hydraulic boom sprayer coupled to a tractor, model Jacto AM-14, with a 14m boom, nozzle spacing of 0,50m and tank capacity of 600L was used. The liquid pressure used was 207kPa and the displacement speeds, for the application volumes of 80L/ha and 130L/ha, were 10km/h and 6km/h, respectively.

To evaluate the application of the herbicide, a study was carried out on the deposition of the spray on weed plants, losses to the soil and losses due to drift. The effectiveness of controlling weeds present in the experimental area was also evaluated. The study of deposition, losses to the soil and drift was carried out by quantifying the herbicide deposited on the targets by liquid chromatography.

After applying the herbicide, deposition assessment was carried out by removing weeds from each plot. They were cut close to the ground and placed in plastic bags. Subsequently, the samples were taken to the laboratory for extraction and determination of the amount of active ingredient deposited. The determination of the active ingredient lost to the soil was carried out by randomly distributing glass slides (37,24 cm²) per installment.

To determine the drift, 2mm diameter nylon wires were placed five meters away, parallel and external to the plots, in the direction of wind displacement. After application, the strands were collected, placed in plastic bags and taken to the laboratory to determine the active ingredient.

In analyzing the effectiveness of weed control, a visual control assessment was carried out 20 days after application of the herbicide (DAA), using the percentage scale of weed control scores (Alam, 1974).

THE OBTAINED RESULTS

The herbicide deposition data on weeds are presented in Table 2. The volume of 80L/ha provided greater deposition on plants when compared to the volume of 130L/ha. The reduction in application volume, combined with the use of a tip with a medium and thick droplet characteristic, did not compromise the efficiency and coverage of the target.

The tips evaluated promoted differences in deposition. The pre-orifice double flat jet tip, with medium droplet size, generated greater deposition on weeds, when compared to the air induction deflector flat jet tip, with extremely thick drops, however, it did not differ from the flat deflector jet, with thick drops. The results suggest that the medium drops were more suitable in terms of deposition on the target, however, the fact that we worked with a double flat jet tip, with medium drops, may also have corroborated this result. In any case, the magnitude of variation between the tips was not large.

In Table 3, the mass of herbicide retained in the plates close to the ground is observed. The volume of 130L/ha provided greater losses to the soil at all ends, when compared to 80L/ha. With this volume, the double flat jet nozzle with pre-orifice led to the lowest loss and the flat deflector jet tip, with air induction, the highest. Very thick drops are heavier and therefore more difficult to retain on the foliage, often having their final destination on the ground. For the volume of 130L/ha, the flat deflector jet nozzle with air induction also caused greater loss, however, it did not differ from the flat deflector jet nozzle.

The methodology used in this test did not provide drift detection. The percentage of weed control, evaluated at 20 DAA (Table 4), was satisfactory, with values ​​between 87,50% and 92,50%, with no difference between treatments.

Final considerations

The application volume of 80L/ha and thick drops can be used to desiccate weeds with the herbicide, without compromising target coverage. Greater loss of herbicide to the soil was observed when flat deflector jet nozzles with air induction were used. However, the different spray tips used, with medium, thick and very thick drops, as well as the application volumes of 80L/ha and 130L/ha, did not influence weed control.

Tabela 1 - Description of evaluated treatments

Treatment	Spray Tip	Volume of syrup (L ha-1)	Drop size classification*	Droplet diameter - DMV (μm)*
1	Pre-orifice dual flat jet - DGTJ60 11002	80	Media	216
2	Pre-orifice dual flat jet - DGTJ60 11002	130	Media	216
3	Flat deflector jet - TT 11002	80	Thick	380
4	Flat deflector jet - TT 11002	130	Thick	380
5	Flat deflector jet with air induction - TTI 11002	80	Extremely thick	925
6	Flat deflector jet with air induction - TTI 11002	130	Extremely thick	925

Treatment

Spray Tip

Volume of syrup

(L ha^-1)

Drop size classification*

Droplet diameter - DMV (μm)*

1

Pre-orifice dual flat jet - DGTJ60 11002

80

Media

216

2

Pre-orifice dual flat jet - DGTJ60 11002

130

Media

216

3

Flat deflector jet - TT 11002

80

Thick

380

4

Flat deflector jet - TT 11002

130

Thick

380

5

Flat deflector jet with air induction - TTI 11002

80

Extremely thick

925

6

Flat deflector jet with air induction - TTI 11002

130

Extremely thick

925

* Classification of droplet size and volumetric median diameter (DMV), according to the manufacturer, at 200kPa pressure.

Tabela 2 - Mass of 2,4-D Amine retained in weed foliage (mg of 2,4-D kg^-1 of wet matter), after applying the herbicide with different spray tips, in two application volumes

Tip	Application volume (L ha-1)		Media
	80	130
Pre-orifice dual flat jet	45,08	42,39	43,73 to
Deflector flat jet	44,87	41,05	42,96 ab
Flat deflector jet with air induction	44,63	37,62	41,13 b
Media	44,86 A	40,35 B

Tip

Application volume (L ha^-1)

Media

80

130

Pre-orifice dual flat jet

45,08

42,39

43,73 to

Deflector flat jet

44,87

41,05

42,96 ab

Flat deflector jet with air induction

44,63

37,62

41,13 b

Media

44,86 A

40,35 B

Means followed by distinct lowercase letters, in the column, and capital letters, in the row, differ from each other, using the Tukey test, at 0,05 probability.

Tabela 3 - Mass of 2,4-D Amine retained on the plate close to the ground (µg of 2,4-D cm^-2), after applying the herbicide with different spray tips, in two application volumes

Tip	Application volume (L ha-1)		Media
	80	130
Pre-orifice dual flat jet	0,99 cB	1,05 bA	1,02
Deflector flat jet	1,16 bB	1,36 aA	1,26
Flat deflector jet with air induction	1,22 aB	1,41 aA	1,32
Media	1,12	1,27

Tip

Application volume (L ha^-1)

Media

80

130

Pre-orifice dual flat jet

0,99 cB

1,05 bA

1,02

Deflector flat jet

1,16 bB

1,36 aA

1,26

Flat deflector jet with air induction

1,22 aB

1,41 aA

1,32

Media

1,12

1,27

Means followed by different lowercase letters, in the columns, and uppercase letters, in the lines, differ from each other, using the Tukey test, at 0,05 probability.

Tabela 4 - Percentage of weed control, evaluated 20 days after herbicide application, with different spray tips, in two application volumes

Tip	Application volume (L ha-1)		Media
	80	130
Pre-orifice dual flat jet	92,50	88,75	90,62
Deflector flat jet	92,50	87,50	90,00
Flat deflector jet with air induction	91,25	87,50	89,37
Media	92,08	87,92

Tip

Application volume (L ha^-1)

Media

80

130

Pre-orifice dual flat jet

92,50

88,75

90,62

Deflector flat jet

92,50

87,50

90,00

Flat deflector jet with air induction

91,25

87,50

89,37

Media

92,08

87,92

This article was published in issue 143 of Cultivar Máquinas magazine. Click here to read the edition.