Variations in Pesticide Doses under Field Conditions - ACS

Chapter 4

Variations in Pesticide Doses under Field Conditions Downloaded by UNIV OF AUCKLAND on September 18, 2017 | http://pubs.acs.org Publication Date (Web): September 11, 2017 | doi: 10.1021/bk-2017-1249.ch004

Pesticide Dose Variation E. D. Velini,*,1 C. A. Carbonari,1 M. L. B. Trindade,2 G. L. G. C. Gomes,1 and U. R. Antuniassi3 1Department of Crop Science, São Paulo State University (Universidade Estadual Paulista “Júlio de Mesquita Filho” UNESP), College of Agricultural Sciences (Faculdade de Ciências Agronômicas), Rua Dr. José Barbosa de Barros 1780, 18.610-307 Botucatu/SP, Brazil 2Bioativa Pesquisa e Compostos Bioativos, Botucatu/SP, Brazil 3Department Rural Engineering, São Paulo State University, College of Agricultural Sciences, Rua Dr. José Barbosa de Barros, 1780, 18610307 Botucatu/SP, Brazil *E-mail: [email protected].

Pesticide doses are most commonly expressed by the volume or weight of the pesticide applied to an area (usually onehectare). However, many plants, insects or microbes can complete their life cycles in environments of only a few cm² or mm². Pesticide doses are not uniform in the field and, on such a small scale, some target organisms survive because they do not receive enough pesticide. Highly variable doses within a field can also contribute to the selection of resistant biotypes, and some target organisms receive doses low enough to show hormesis. The information available consistently shows highly variable pesticide deposition or concentrations in individual leaves, plants (crops or weeds) and soil samples. Because of dose variability in the field, higher mean doses are necessary to achieve satisfactory control levels. Weeds compete for spray droplets, and higher weed populations can reduce the individual doses deposited. The presence of heterogeneous amounts of

© 2017 American Chemical Society Duke et al.; Pesticide Dose: Effects on the Environment and Target and Non-Target Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 2017.

straw on the soil can contribute to increased variation in the doses of pre-emergence herbicides and the possibility of other classes of pesticides being transported to the soil by rain water.

Downloaded by UNIV OF AUCKLAND on September 18, 2017 | http://pubs.acs.org Publication Date (Web): September 11, 2017 | doi: 10.1021/bk-2017-1249.ch004

Introduction Pesticide doses under field conditions are not uniform. The dose applied corresponds to the mean dose observed in the field in the absence of losses due to drift. The few studies that have addressed variation in pesticide doses under field conditions have shown that the deposition of pesticides in plants, leaves or individually assessed targets can vary by orders of magnitude. The consequence of this variation is the establishment of a myriad of combinations of doses and selection pressures after the application of a pesticide at a previously selected dose that should be uniform (1). Even when a sublethal dose of an herbicide is applied, some plants will receive very high doses that are above the expected mean dose. Similarly, the use of high doses is not sufficient to ensure that plants are not subjected to sublethal doses of herbicides. A high dose of herbicide results in high mortality in the plants that receive it, but it can select rare resistance genes capable of producing a high-level of resistance; in contrast, low doses of herbicide (many plants die, but some survive) select all possible resistance genes, including genes for both high- and low-level resistance (2). Previous studies have shown that vertical and horizontal movements of the spray boom (3–6), protection by mulch (7) and protection by weeds or cultivated plants (8–10) can cause variation in single pesticide doses under field conditions. Gazziero et al. (9) and Souza et al. (10) assessed the variation in the doses deposited in early weeds in the soybean crop. The analysis of the data indicated that the variation was sufficient for some weeds to receive sufficiently low doses for hormetic effects to occur. Hormesis is the stimulation of growth by low levels of inhibitors (11–13). Among pesticides, herbicide hormesis has been studied more frequently. Several papers have discussed the hormetic effects of glyphosate (14–17) or herbicides in general (18, 19). For most pesticides applied to plants, their actions do not depend on deposition alone because they need to be absorbed to be toxic to the plants, insects or pathogens. The limited information available in the literature does not allow any conclusions about the effects of deposition and absorption processes in making pesticide concentrations in plant tissues more or less uniform.

Variation of Doses under Field Conditions Nation (4) studied the variation of doses applied with the use of new sprayers using targets with a 25-cm² surface. The author observed that the deposition coefficients of the spray deposits ranged from 27 to 98%. The variation between the largest and smallest deposits for each application ranged between 3.9 and 28-fold; the variation could not be determined for two applications for which the 48 Duke et al.; Pesticide Dose: Effects on the Environment and Target and Non-Target Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


minimum deposit was null. The lowest deposition expressed as the percentage of the mean for each application was 0%, whereas the maximum deposition was 253%. The author concluded that the spray boom movements were the main factor responsible for the variation in doses, that the boom movements primarily occurred due to the transmission of motion of the sprayer, and that the variation could be considerably reduced using spray boom stabilizers. Notably, 25-cm² targets can be quite large when considering the size of the soil area required for a seed or a fungal spore to germinate. A similar study (6) concluded that the horizontal movements of the spray boom were the most relevant factors in terms of dose variation and that the variation was larger when flat fan nozzles were used compared to the use of hollow cone jets. The coefficients of deposit variation estimated for the different operating conditions ranged from 6.7 to 64%. Increasing the boom height from 0.5 m to 0.9 m reduced the coefficients of variation of the deposits. The vertical movements of the spray boom also led to variation in pesticide doses (5). Considering the 22 experimental conditions evaluated, the coefficients of variation of the deposits ranged from 1.84 to 116.22% as a result of those movements. Under the condition with the lowest coefficient of variation, the doses ranged between 98 and 102% of the mean. Under the condition with the highest coefficient of variation, the doses ranged between 0 and 760% (5) Keenes et al. (20) studied the effects of pendulum, simple and double trapezium suspensions in reducing the vertical movements of the spray boom and concluded that the three models could be very effective. Boom stabilizers have been widely used in modern sprayers, especially those that operate at higher speeds and use longer booms. Tofoli (21) studied the uniformity of the spray deposition at ground level. The application speed was 4 km/h. Two similar sprayer sets were used with booms 12 m wide and nozzles spaced at 0.5-m intervals. At the time of spray application, the temperature was 25 °C and the relative humidity was 46%. The Conic Jet Nozzle model JA 1.5 and Fan Jet Nozzle model API11002 nozzle types were evaluated under normal operating conditions. Round targets made of Formica® were used to evaluate the amount of spray deposited in areas with diameters of 0.3175, 0.635, 1.27, 2.54, 5.08 and 10.16 cm. A total of 117 targets of each size were used for each nozzle type. The main results obtained are presented in Table 1. For the two smaller target sizes (0.3175 and 0.635 cm), the variation in spray deposition was very high. For the smallest target size (0.3175 cm), the spray deposition ranged between 38.25 and 249.65% and between 14.32 and 392.71% of the mean for the Fan Jet API 11002 and Conic Jet JA 1.5 nozzles, respectively. The results obtained for the remaining target sizes (1.27 to 10.16 cm) were similar. Higher coefficients of variation were observed for the Fan Jet API 11002 nozzle, but the largest spray deposition was obtained using the Conic Jet JA 1.5 nozzle. Even for the largest targets tested, the spray deposition ranged between 68.04 and 128.26% and between 38.68 and 154.66% of the mean for the Fan Jet API 11002 and the Conic Jet JA 1.5 nozzles, respectively.

49 Duke et al.; Pesticide Dose: Effects on the Environment and Target and Non-Target Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 2017.

50


Table 1. Minimum and Maximum Deposition, Deposition Amplitude and Coefficient of Variation of the Deposition Observed for Different Target Sizes and Nozzle Types (21). Nozzle type

Fan Jet API11002

Conic Jet JA 1.5

Target size (cm) 0.3175

0.635

1.27

2.54

5.08

10.16

Minimum deposition (% of the mean)

38.25

41.42

50.09

62.95

60.35

68.04

Maximum deposition (% of the mean)

249.65

187.36

135.34

128.72

135.39

128.26

Deposition amplitude (% of the mean)

211.40

145.94

85.25

65.77

75.04

60.22

Maximum deposition/Minimum deposition

6.53

4.52

2.70

2.04

2.24

1.89

Coefficient of Coefficient of variation (%)

78.76

49.17

22.36

19.24

20.89

18.01

Minimum deposition (% of the mean)

14.32

33.81

36.94

47.27

44.12

38.68

Maximum deposition (% of the mean)

392.11

304.46

157.42

153.92

154.22

154.66

Deposition amplitude (% of the mean)

377.79

270.66

120.48

106.66

110.10

115.98

Maximum deposition/Minimum deposition

27.38

9.01

4.26

3.26

3.50

4.00

Coefficient of Coefficient of variation (%)

59.27

45.89

25.95

25.11

26.31

28.56

Duke et al.; Pesticide Dose: Effects on the Environment and Target and Non-Target Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


Silva (8) studied the effects of Cyperus rotundus population densities and operational characteristics, including nozzle types, in the deposition of spray solution on the plants and acrylic plates simulating the soil of infested areas. The evaluated C. rotundus population densities are representative of those that occur in agricultural areas. The results presented in Table 2 were obtained using XR 11002 nozzles at a 0.5 m height from the targets spaced 0.5 m apart and operating at 2.5 bar and 3.2 km/h with a flow rate of 193 L/ha. With an increase in the population density from 300 to 1200 plants/m², the amount of spray solution deposited in each plant was reduced by 29% (from 14.57 to 10.32 µL/plant). Because C. rotundus population densities are not uniform in the field, the results indicate that the variations in population density can lead to variations in the doses received by each plant, which is quite relevant when the herbicide applied acts exclusively at the post-emergence stage and has no activity on the soil. The results indicate that isolated plants tend to receive higher doses than plants on highly infested patches, which can contribute to the patchiness of C. rotundus populations. The percent deposition of spray solution in the plants increased with the increasing population density of the weed, even with the reduction of deposits in each individual plant. The results indicate that the doses of post-emergence herbicides received by each plant and the probability of survival depend on the number of plants around it (i.e., the population density).

Table 2. Effects of the Cyperus rotundus L. Population Densities on the Deposition of the Spray Solution (8). Plants/m²

Deposition

Percent of total deposition in the targets

µL/plant

Soil

Plant

300

14.57

79.07

20.93

600

12.67

45.35

54.65

900

13.23

45.04

54.96

1200

10.32

38.75

61.25

Gazziero et al. (9) evaluated the deposition of a glyphosate solution in soybean and wild poinsettia plants (Euphorbia heterophylla). Glyphosate was applied 17, 24, 31, 38 and 45 days after soybean emergence. Glyphosate application was performed using XR 110-015 nozzles pressurized at 2.07 bar and consuming 150 L of spray solution/ha. For the evaluations at 17 and 31 days after soybean emergence, the frequencies as a function of the depositions expressed in µL/cm² or µL/plant are shown in Figures 1 and 2. Although spray deposition expressed as µL/plant increased with the crop age, the spray deposition on soybean or wild poinsettia plants expressed in µL/cm² decreased progressively with crop growth, with possible negative effects on the efficacy of herbicides 51 Duke et al.; Pesticide Dose: Effects on the Environment and Target and Non-Target Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


directed at the weeds or fungicides and insecticides directed to the crop. Later applications produced less uniform spray depositions on the soybean and wild poinsettia plants, possibly contributing to the lack of control on plants that received lower doses.

Figure 1. Spray deposition on soybean and wild poinsettia plants (µL/plant) 17 and 31 days after crop emergence (DAE) (9).

Figure 2. Spray deposition on soybean and wild poinsettia plants (µL/cm²) 17 and 31 days after crop emergence (DAE) (9). Souza et al. (10) observed that the crop itself could capture drops of the spray solution, thereby reducing the amount available for weeds. The authors found that Brachiaria plantaginea plants located in the soybean planting row received 34% less herbicide than plants in the inter-rows and that in the same location the 52 Duke et al.; Pesticide Dose: Effects on the Environment and Target and Non-Target Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


spray deposits were proportional to the foliar areas of the weed. Therefore, similar to the results obtained by Gazziero et al. (9), Souza et al. (10) found that larger soybean plants received higher spray depositions if expressed in µL/plant but lower depositions when the data were expressed in µL/cm². Carbonari and Velini (22) studied the uniformity of herbicide deposition in 30 commercial applications of pre-emergence herbicides in sugarcane. The herbicide depositions were individually evaluated with 15 to 30 glass plates (10 cm x 20 cm) positioned on the soil or glass surface. For the 30 applications, the number of sampled points was 635. Notably, 0.62% and 3.94% of the targets received less than 30% and less than 50% of the planned dose, respectively (Figure 3). Only 0.94% of the targets received more than 120% of the planned dose. When the deposition was expressed as the percentage of the mean value observed for each application (Figure 4), the deposition was between 80 and 120% for 82.83% of the targets and more than 50% for all targets. The spray deposition was more than 150% of the mean deposition observed in the respective application for only three targets (0.47%). The variation in spray deposition observed by the authors might be quite significant and contribute to weed control failures or crop damage under field conditions. In agreement with the previous study (23–26), the authors observed that the amount of straw in raw cane, the time interval between the herbicide application and the first rainfall event and the rainfall depth could change the amount of herbicide transported to the soil. The increased amount of straw reduced the transport of herbicides to the soil primarily when the initial rains were scarce (less than 20 mm). Because the distribution of straw in the field is not uniform, the presence of this crop waste can increase the variation in the single doses that reach the soil.

Figure 3. Deposition of herbicides applied to sugarcane fields expressed as the percentage of the planned dose (22). 53 Duke et al.; Pesticide Dose: Effects on the Environment and Target and Non-Target Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


Figure 4. Deposition of herbicides applied to sugarcane fields expressed as the percentage of the mean deposition for each application (22).

Figure 5. Deposition of spray solutions on individual leaves of adult orange trees (27). Concerning variations in pesticide doses in fruit trees, Palladini (27) evaluated the deposition of spray solutions with surface tensions of 0.0728 N/m (equivalent to the surface tension of water) and 0.0365 N/m (achieved with the addition of surfactant) in mature orange trees. The spray volume was 1.830 L/ha or 5.1 L/plant. In the areas tested, 600 leaves were collected from 12 different positions on the plants. The databases built contained 600 data points regarding deposition on individual leaves for each of the two treatments evaluated. Figure 5 shows the accumulated frequencies as a function of the deposits expressed in µL/cm². The deposition data are summarized in Table 3. Regardless of the surface tension, the deposits in µL/cm² were very heterogeneous, with certain 54 Duke et al.; Pesticide Dose: Effects on the Environment and Target and Non-Target Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


leaves receiving doses significantly above or below the observed mean. The relationships between the minimum and maximum deposits were 55.0 and 32.9 and the coefficients of variation were 64.37% and 58.67% for the treatments with surface tensions of 0.0728 N/m and 0.0365 N/m, respectively. The non-uniform deposition in individual leaves can reduce the effectiveness of fungicides and insecticides applied in orange trees or demand larger doses for the pesticide dose to be sufficient for the control of the target organism, even in leaves with a lower spray deposition. The results obtained by Antuniassi et al. (28) provided evidence of the variation in fungicide deposition in individual leaves of adult peach trees. The authors assessed fungicide deposition in six applications performed under different operating conditions corresponding to distinct combinations of sprayer speed and wind speed. The consumption of the spray solution was measured at the end of each application and ranged from 825 to 927 L/ha. After application, 300 leaves were collected from five different positions in the plants. Therefore, databases were built containing 300 data points regarding the deposition of the spray solution in individual leaves. The results were expressed as µL/cm² (Figure 6) or as percentage of the mean deposits observed (Figure 7). The data obtained are summarized in Table 4. The range between the minimum and maximum deposits was 11.2, 9.7, 33.4, 119.9, 13.2 and 13.9 for applications 1 to 6, respectively. The coefficients of variation were between 37.1% and 53.6%, and the minimum and maximum values were observed for applications 2 and 4, respectively. When the deposition is represented as the percentage of the mean observed for each application, the results obtained for the six sets of operating conditions evaluated were very similar. The variation in the deposition of the spray solution in the leaves of adult peach trees was significant and could compromise the effectiveness of fungicide treatments applied to the crop under the evaluated operating conditions.

Figure 6. Deposition of spray solution on individual leaves of adult peach trees expressed as µL/cm² (28). 55 Duke et al.; Pesticide Dose: Effects on the Environment and Target and Non-Target Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 2017.

Surface Tension

µL/cm²

µL/cm²

µL/cm²

% of the mean

% of the mean

Coefficient of

(N/m)

Minimum

Mean

Maximum

Minimum

Maximum

variation (%)

0.0728

0.116

1.505

6.358

7.67

422.33

64.37

0.0365

0.165

1.636

5.443

10.12

332.80

58.67

56


Table 3. Minimum, mean, and Maximum Deposition and Coefficient of Variation of Spray Deposition in Individual Leaves of Adult Orange Trees (27).


Applications

µL/cm²

µL/cm²

µL/cm²

% of the mean

% of the mean

Coefficient of

Minimum

Mean

Maximum

Minimum

Maximum

variation (%)

1

0.32

1.28

3.58

24.9

278.8

47.5

2

0.38

1.47

3.73

26.2

253.6

37.1

3

0.14

1.41

4.60

9.8

327.5

52.0

4

0.04

1.85

4.75

2.1

256.1

53.6

5

0.34

1.55

4.46

21.8

287.1

46.6

6

0.24

1.30

3.38

18.7

260.0

46.1

57


Table 4. Minimum, Mean, and Maximum Deposition and Coefficient of Variation of Spray Deposition in Individual Leaves of Adult Peach Trees (28).



Figure 7. Deposition of spray solution on individual leaves of adult peach trees expressed as the percentage of the mean for each application (28).

Conclusion The first point worth noting is the apparent inconsistency between the results presented on variations of pesticide doses in the field and the consistency of the control exerted by these products under normal application conditions. Low-effectiveness applications are of little use to farmers and high effectiveness can be achieved even in non-uniform applications by increasing the mean dose applied. As C. rotundus population densities are not uniform in the field, variations in population density can lead to variations in the doses received by each plant, which is quite relevant when the herbicide applied acts exclusively at the post-emergence stage and has no activity on the soil (8). The research was limited to C. rotundus, but similar results might be obtained for any weed species or species association. The soybean crop itself reduced the deposition of spray solution in Brachiaria plantaginea plants (10). The data shown in this chapter are apparently inconsistent with the uniformity of the spray flow rate and deposition along spray booms observed in standardized tests conducted in patternators. The standard tests are carried out under static conditions and over long periods of time for the data to be stable and representative. In contrast, under field conditions, individual targets, plants or leaves are exposed to the application droplets for very short periods of time. For example, in an application with a flat fan nozzle at 5 km/h in which 5 cm is considered the thickness of the cloud drops, targets (plant, leaf or soil area) with a 1 cm or 10 cm length would be exposed to drops for only 0.144 s and 0.0792 s, respectively. At this time scale, the effects of the horizontal and vertical movements of the spray boom can lead to large individual variations in pesticide deposition. 58 Duke et al.; Pesticide Dose: Effects on the Environment and Target and Non-Target Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 2017.


Many of the studies discussed here refer to the application of herbicides, but the data presented (9, 10) may help better illustrate the variations in the deposition of other pesticide classes in crops. The studies by Antuniassi et al. (28) and Palladini (27) assessed the variation in fungicide, insecticide or fertilizer deposition in individual leaves of adult orange and peach trees using air-carrier sprayers. Additionally, the doses used in these studies were very heterogeneous, indicating that high variability was not restricted to boom sprayers. The presence of heterogeneous amounts of straw on the soil can contribute to increased variation in the doses of pre-emergence herbicides and the possibility of other classes of pesticides being transported to the soil by rain water, thereby impacting their effectiveness and environmental dynamics. Highly variable individual doses under field conditions can be compatible with high effectiveness if the average planned dose is high enough for the most of the target organisms to receive lethal doses. In order to achieve acceptable efficacy levels, the less uniform the individual doses, the higher must be the average planned dose. Different doses or spatial arrangements of doses in the field can exert different selection pressures, possibly contributing to the selection of biotypes resistant to the different pesticide classes.

References 1.

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12. Calabrese, E. J. Environ. Toxicol. Chem. 2008, 27, 1451–1474. 13. Calabrese, E. J. Hum. Exp. Toxicol. 2010, 29, 249–261. 14. Velini, E. D.; Alves, E.; Godoy, M. C.; Meschede, D. K.; Souza, R. T.; Duke, S. O. Pest. Manage. Sci. 2008, 64, 489–496. 15. Belz, R. G.; Leberle, C. Julius-Kühn-Arch. 2012, 434, 427–434. 16. Cedergren, N.; Olesen, C. F. Pestic. Biochem. Physiol. 2010, 96, 140–148. 17. Silva, F. M. L.; Duke, S. O.; Dayan, F. E.; Velini, E. D. Weed Res. 2016, 56, 124–136. 18. Belz, R. G.; Duke, S. O. Pest Manage. Sci. 2014, 70, 698–707. 19. Cedergreen, N.; Felby, C.; Porter, J. R.; Streibig, J. C. Field Crop Res. 2009, 114, 54–57. 20. Kennes, P.; Ramon, H.; De Baerdemaeker, J. J. Agric. Eng. Res. 1999, 72, 217–229. 21. Tofoli, G. R. Irregularity of pesticide spray deposition as affected by nozzle type and target size. Master Thesis, Faculdade de Ciências Agronômicas, Universidade Estadual Paulista, Botucatu, SP, Brazil, 2001. 22. Carbonari C. A.; Velini, E. D. 2016. Faculdade de Ciências Agronômicas / Universidade Estadual Paulista. Drift and deposition of herbicides applied to sugarcane fields. Botucatu / SP – Brazil. Unpublished dataset, cited with permission. 23. Carbonari, C. A.; Gomes, G. L. G. C.; Trindade, M. L. B.; Silva, J. R. M.; Velini, E. D. Weed Sci. 2016, 64, 201–206. 24. Cavenaghi, A. L.; Rossi, C. V. S.; Negrisoli, E.; Costa, E. A. D.; Velini, E. D.; Toledo, R. E. B. Planta Daninha 2007, 25, 831–837. 25. Tofoli, G. R.; Velini, E. D.; Negrisoli, E.; Cavenaghi, A. L.; Martins, D. Planta Daninha 2009, 27, 815–821. 26. Rossi, C. V. S.; Velini, E. D.; Luchini, L. C.; Negrisoli, E.; Correa, M. R.; Pivetta, J. P.; Costa, A. G. F; Silva, F. M. L. Planta Daninha 2013, 31, 223–230. 27. Palladini, L. Methodology for the evaluation of spraying deposits. Ph.D. Thesis, Faculdade de Ciências Agronômicas, Universidade Estadual Paulista, Botucatu, SP, Brazil, 2000. 28. Antuniassi, U. R.; Velini, E. D.; Martins, D. Spray deposition and drift evaluation of air carrier peach orchard sprayer. In International Conference on Agricultural Engineering, 1996, Madrid; Universidade Politécnica de Madrid: Madrid, Spain, 1996; pp 279−280.

60 Duke et al.; Pesticide Dose: Effects on the Environment and Target and Non-Target Organisms ACS Symposium Series; American Chemical Society: Washington, DC, 2017.

Variations in Pesticide Doses under Field Conditions - ACS

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