A COMPARISON OF NEW SPRAY TECHNOLOGY FOR DISEASE

CONTROL IN SOUTH AFRICA

ZILUNGISELE S. MAVUSO

zilungiselem@westfaliafruit.co.za

A COMPARISON OF NEW SPRAY TECHNOLOGY FOR DISEASE

CONTROL IN SOUTH AFRICA

Z. S. Mavuso 1, Z. Van Rooyen 1 and A. Boyum1 1. Westfalia Fruit Estate, Tzaneen, South Africa

The use of pesticides in agriculture is still the most widespread method for avocado diseases

control world-wide. Successful control of avocado diseases mostly depends on correct choice of

agrochemicals, equipment and proper application methods. Environmental and (potential) human

health problems related to the use of agrochemicals have created an increasing resistance to their

use. Therefore, application methods are continuously investigated to ensure an adequate, yet

efficient, application of pesticides.

Various spray application equipment were compared for disease control (and water use) at

Westfalia Fruit Estates in the Limpopo Province, South Africa. These included high volume hand

guns, traditional mist-blowers and the newer technology of Electrostatic spray technology. Trials

were conducted on both ‘Hass’ and ‘Fuerte’ avocado cultivars comparing various agrochemical

spray formulations.

The results indicated that mist blower application was as effective and cheaper than hand guns.

New spray technology such as electrostatic spraying achieved better crop coverage, while

achieving effective disease control while using less water and up to 50% less chemicals than

current commercial spraying.

The newer spray technology with a more even droplet distribution and coverage show good

potential. However, the challenge with electrostatic mist-blowers might be in adjusting the current

agrochemicals as per (the original) label.

Keywords South Africa, avocado, diseases, agrochemicals, spray technology

COMPARACION DE UNA NUEVA TECNOLOGIA DE PULVERIZACION

PARA EL CONTROL DE ENFERMEDADES EN SUDAFRICA

El uso de pesticidas en la agricultura sigue siendo el método más extendido para el control de

enfermedades del aguacate en todo el mundo. El control exitoso de las enfermedades del aguacate

depende principalmente de la correcta elección de los agroquímicos, del equipo y el método de

aplicación adecuado. Los problemas ambientales y de salud humana (potenciales) relacionados

con el uso de agroquímicos han creado una creciente resistencia a su uso. Por esta razón, distintos

métodos de aplicación están siendo investigados continuamente para garantizar una adecuada y a

la vez eficiente aplicación de pesticidas.

Se compararon distintos equipos pulverizadores para el control de enfermedades (y el uso del agua)

en Westfalia Fruit Estates en la provincia de Limpopo, Sudáfrica. Estos incluyeron el pistón/pistola

manual de alto volumen, los nebulizadores tradicionales y la más nueva tecnología, la

pulverización electrostática. Se realizaron ensayos en los cultivares "Hass" y "Fuerte",

comparándose distintas formulaciones.

Los resultados indicaron que la nebulización fue tan efectiva y económica como el pistón/pistola

manual. La nueva tecnología de pulverización, como la pulverización electrostática, logró una

mejor cobertura, un control efectivo de la enfermedad, utilizando menos agua y hasta un 50%

menos de productos químicos que la pulverización comercial actual.

la nueva tecnología de pulverización con una cobertura y distribución de gotas más uniforme,

muestra un buen potencial. Sin embargo, el desafío con los nebulizadores electrostáticos puede ser

el ajustar los actuales agroquímicos según la etiqueta (original).

Palabras clave Sudáfrica, aguacate, enfermedades, agroquímicos, tecnología de pulverización

Introduction

Avocado production is concentrated mainly in the warm and humid subtropical areas in South

Africa. Several diseases affect South African avocado fruit such as Cercospora spot, anthracnose

and stem-end rot (Mavuso, Willis, and Niekerk, 2015). The use of chemical fungicides to control

diseases is an essential element of crop management. Diseases on avocado are usually controlled

by high volume applications of copper fungicides during the rainy period. Due to the changes in

the European Union (EU) legislation regarding the use of other systemic fungicides like Benomyl

and azoxystrobin, copper containing fungicides remain the most commonly used and available

fungicides on avocado. The presently growing need to reduce the amount of copper applied to

orchards is driven by export markets as well as the future sustainability of farming operations

(Willis, 2007). Therefore, there is a need to look for an alternative approach to reduce the amount

of copper applied to orchards.

Fungicides applications are one of the least pleasant tasks on a farmer’s to-do list but are something

that must be done. Typically, growers apply fungicides based on application instructions on

product labels while incorporating advice from a crop specialist (Curley, 2018). Successful control

of avocado diseases does not only depend on the correct choice of fungicides but also the

equipment used. However, it is not only the equipment itself, but everything related to the

application of plant protection products that need to be taken into account in order to improve the

results obtained, like knowing what technologies are available to help growers improve their spray

applications in a more effective, efficient and sustainable way (Gil et al., 2014).

Spray technology on avocado has been undergoing continuous evolution in recent decades. For

the past years, thermal fogging fungicides with a PulsFog® unit was found to be effective for more

resistant cultivars (Hass and Ryan) without leaving a residue as with handgun applications. Copper

oxychloride could not be used because it clogged the machine and flowable formulations like

copper ammonium carbonate were recommended. Spraying should only be done in windless

conditions before or after the heat of the day (Duvenhage & Köhne, 1999). (Willis, 2007) found

that mist blower applications at 5 000L/ha four times per season were effective in controlling

Cercospora spot on ‘Fuerte’ at Westfalia Estate rather than handgun applications at14 000L/ha

three times per season using copper oxychloride 3g/L. Mist blower application was also cheaper

than hand gun applications (Mavuso et al., 2015).

A non-thermal compressed air aided ultra-low volume (ULV) fogging machine technology was

tested at Westfalia Fruit Estate on a small scale between 2008 and 2011(Mavuso et al., 2015; Van

Niekerk and Mavuso, 2011). The results showed that this application technology had the potential

for avocado disease control, however, spraying should only be done in windless conditions before

or after the heat of the day.

Owing to the difficulty in reaching targets during fungicides applications on avocado trees, it is

important to evaluate new technologies that may improve pest management (Marcos et al., 2013).

Currently, Westfalia Fruit Estate is evaluating the efficacy of a Pneumatic-Electrostatic Mist-

blower compared to a commercial mist blower. Electrostatic spray technology was invented in the

early 1930's and the aim was to improve spray deposition on the canopy (Mishra et al., 2014). In

this type of application biological efficacy is better with less chemical waste and drift. After early

1980's electrostatic spraying equipment was worked on for the agricultural community (Urkan,

Guler, and Komekci, 2016).

Materials and methods

Fungicides application and treatments

The experiment was carried out at Westfalia Estate in the Limpopo Province, South Africa. This

region has a high potential for avocado diseases especially Cercospora spot infection due to the

climate. The experiment was conducted on two cultivars ‘Fuerte’ and ‘Hass’.

‘Fuerte’

Thirty years old ‘Fuerte’ trees were used. Different copper oxychloride concentrations using

Pneumatic-Electrostatic Mist blower were tested in comparison with standard copper oxychloride

using high volume mist blower application. Four applications were done per season (October,

November, December and January). Refer to table 1 for treatment details.

‘Hass’

Fifteen years old Hass trees were used. Different formulations and concentrations of copper

oxychloride were tested using mist blower in comparison with Pneumatic-Electrostatic Mist-

blower equipment. Two applications were done per season (December and January). Refer to table

2 for treatment details.

Trial evaluation

On ‘Fuerte, ’the trial was harvested at the end of May 2018 in order to allow for maximum disease

development. In each treatment, One hundred and sixty fruit (size 16) were randomly picked from

data trees and evaluated for incidence and severity of Cercospora spot and visible spray residues

upon harvest, while on Hass one hundred and twenty-eight fruit (size 16) were randomly picked

from each treatment and evaluated for incidence and severity of Cercospora spot, pepper spot and

visible spray residues upon harvest during June 2018.

The observed symptoms were rated based on a scale of 0 - 3 where fruit with a 0 is clean fruit, 0

and 1 rating is marketable and fruit with a 2 and 3 rating are unmarketable. After harvest, fruit

were stored for 28 days at 5.5 °C before being ripened at 22 °C. After ripening fruit were evaluated

for the presence and severity of stem-end rot and anthracnose symptoms using the abovementioned

rating scale. Following the evaluation, the percentage clean fruit based on disease symptom ratings

for each treatment was calculated. There was no enough variation to do statistical analysis.

Results and Discussion

‘Fuerte’

There was extremely high disease pressure in the trial orchard as indicated by the high incidence

of Cercospora spot in the untreated control (Table 3).

The results showed that using Pneumatic-Electrostatic Mist-blower 12g/L and 24g/L of Copper

Oxychloride WP @1000L/ha is as equally effective as using commercial standard mist blowers

(Ultima & Bateleur) 3g/L of Copper Oxychloride WP @ 8200L/ha in terms of Cercospora spot

control. Using Pneumatic-Electrostatic Mist-blower 6g/L of Copper Oxychloride WP @ 1000L/ha

was less effective than the commercial standard (Table 3). In terms of visible copper spray resides,

6g/L and 12g/L using Pneumatic-Electrostatic Mist-blower @ 1000L/ha resulted in more clean

fruit than the commercial standard. Pneumatic-Electrostatic Mist-blower also gives a good

coverage on the leaves (Figure 1.). Commercial standard mist blower resulted on bigger chemical

droplet size and leave spaces in between which gives a pathogen an opportunity to cause an

infection (Figure 2.). Using Pneumatic-Electrostatic Mist-blower can also save water

(7200L/ha/application) which can be used for other purposes (Table 3.). It must be noted that using

Pneumatic-Electrostatic Mist-blower @1000L/ha and 6g/L, 12g/L and 24g/L is not as per label of

copper oxychloride. There was no difference in terms of post-harvest diseases, the fruit in all the

treatments were free from diseases (data not included).

‘Hass’

The results showed that using Pneumatic-Electrostatic Mist-blower 3g/L Copper Oxychloride WP

@ 750L/ha is as equally effective as using commercial standard mist blowers (Ultima) 3g/L of

Copper Oxychloride WP @ 2000L/ha in terms of Cercospora spot and pepper spot control. The

amount of active copper used was 30% and water was 37% of the commercial standard. Using

Pneumatic-Electrostatic Mist-blower 10ml/L of NanoGreen SC @ 750 L/ha is equally effective as

using commercial standard (Ultima) 2.5ml/L of the same product @ 2000L/ha (Table 4.). The

results confirm the work done by Patel et al. (2015) which indicated that electrostatic nozzles were

highly efficient, reduces pesticide use and human health risks, and eco-friendly.

Unlike conventional spray droplets, which contain an equal number of positively charged protons

and negatively charged electrons, spray droplets emitted through an electrostatic system receive a

positive or negative charge from electrodes surrounding each nozzle. As the charged spray droplets

reach the target, they induce an opposite charge on the leaf, thus activating electrostatic forces and

attracting the charged droplets to both the upper and under leaf surfaces (Urkan et al., 2016).

Because of the size of the droplets produced by electrostatically, the coverage on tops and

undersides of leaves is better than conventional spraying.

Conclusion

New spray technology such as electrostatic spraying achieved better crop coverage while

achieving effective disease control while using less water and up to 50% on Fuerte and 30% on

Hass less chemicals than current commercial spraying on. The newer spray technology with a more

even droplet distribution and coverage show good potential. However, the challenge with

electrostatic mist-blowers might be in adjusting the current agrochemicals as per (the original)

label. It was possible to reduce the volume rate of application with electrostatic spraying without

adversely affecting the control of the disease.

References

Curley, M. (2018). Increasing farm efficiency with best practices for spray application. Retrieved

11 June 2018, from https://www.canr.msu.edu/news/increasing-farm-efficiency-with-best-practices-for-

spray-application

Duvenhage, J. A., and Köhne, J. S. (1999). Thermal fogging of fungicides for the control of

Pseudocercospora purpurea on avocado. South African Avocado Growers’ Association. P. 88–

90.

Gil, E., Arnó, J., Llorens, J., Sanz, R., Llop, J., Rosell-polo, J. R., and Escolà, A. (2014). Advanced

Technologies for the Improvement of Spray Application Techniques in Spanish Viticulture: An

Overview, (March). https://doi.org/10.3390/s140100691

Marcos, P., Monteiro, D. B., Rodrigues, D. E., and Alvarenga, C. B. De. (2013). Parameters of

electrostatic spraying and its influence on the application efficiency1. Rev. Ceres, Vicosa v. 60,

n.4, p. 474–479.

Mavuso, Z. S., Willis, A., and Niekerk, J. M. Van. Challenges of growing avocado’s in subtropical

South Africa. VIII World Avocado Congress, Peru, 13 – 15 September 2015. p170–174.

Mishra, P. K., Singh, M., Sharma, A., Sharma, K., and Singh, B. (2014). Studies on effect of

electrostatic spraying in orchards. Agricultural Engineering International: CIGR Journal, 16(3),

p60–69.

Patel, M. K., Sahoo, H. K., Nayak, M. K., Kumar, A., Ghanshyam, C., & Kumar, A. (2015).

Electrostatic Nozzle : New Trends in Agricultural Pesticides Spraying. SSRG International Journal

of Electrical and Electronics Engineering. p 6–11.

Urkan, E., Guler, H., and Komekci, F. (2016). A review of electrostatic spraying for agricultural

applications. Journal of Agricultural Machinery Science, 12(4), p.229–233.

Van Niekerk, J. M., and Mavuso, Z. S. Evaluation of ultra-low volume (ULV) fungicide

applications for the control of diseases on avocado fruit – Results from the 2009 / 10 season. 7th

World Avocado Congress, Cairns, Australia, 5-9 September 2011.

Willis, A., and Mavuso, Z. S. Evaluation of alternative fungicides for control of cercospora spot

on ‘Fuerte .’ VI World Avocado Congress, Vina Delma, Chile, 12 – 16 November 2007. P. 579–

583.

Table 1: Spray equipment and amount of fungicides applied per ha per year in the 2017-2018

season on ‘Fuerte’.

Treatment no. Spray equipment Fungicide application

1 Ultima and Bateleur mist blower 4x Copper Oxychloride WP 3g/L

@ 8200L/ha

2 Pneumatic-Electrostatic Mist-

blower

4x Copper Oxychloride WP 6g/L

@ 1000L/ha

3 Pneumatic-Electrostatic Mist-

blower

4x Copper Oxychloride WP 12g/L

@ 1000L/ha

4 Pneumatic-Electrostatic Mist-

blower

4x Copper Oxychloride WP 24g/L

@ 1000L/ha

5 Untreated

Table 2: Equipment and amount of fungicides applied per ha per year in the 2017-2018 season on

Hass.

Treatment

no.

Spray equipment November application January application

1 Ultima mist blower Cuprous oxide WG 1g/L

@ 1500L/ha

Copper Oxychloride WP

3g/L @ 2000L/ha

2 Pneumatic-Electrostatic

Mist-blower

Cuprous oxide WG 1g/L

@ 750L/ha

Copper Oxychloride WP

3g/L @ 750L/ha

3 Ultima mist blower NanoGreen SC 2.5ml/L

@2000L/ha

NanoGreen SC 2.5ml/L

@2000L/ha

4 Pneumatic-Electrostatic

Mist-blower

NanoGreen SC 10ml/L

@750L/ha

NanoGreen SC 10ml/L

@750L/ha

5 Untreated

Table 3: Equipment, amount of fungicide and water applied per ha per year and percentage clean

fruit free from Cercospora spot and visible copper residues on ‘Fuerte’.

Equipment

Fungicides and

water applied Active

kgCu/ha/yr

% clean fruit

free from

Cercospora

% clean fruit free

from visible

copper residues

Ultima &

Bateleur

4x Copper

oxychloride WP

3g/L @8200L/ha 49 100 0

Pneumatic-

Electrostatic

Mist-blower

4x Copper

oxychloride WP

6g/L @1000L/ha 12 74 76

Pneumatic-

Electrostatic

Mist-blower

4x Copper

oxychloride WP

12g/L @1000L/ha 24 100 29

Pneumatic-

Electrostatic

Mist-blower

4x Copper

oxychloride WP

24g/L @1000L/ha 48 100 2

Untreated

0 0 100

Table 4: Equipment, amount of fungicide and water applied per ha per year and percentage clean

fruit free from Cercospora spot, pepper spot and visible copper residues on Hass.

Equipment

Fungicides and

water applied

Active

kgCu/ha/yr

% clean

fruit free

from

Cercospora

% clean

fruit free

from

pepper spot

% clean fruit

free from

visible copper

residues

Ultima mist

blower

Cuprous oxide WG

1g/L @ 1500L/ha and

Copper Oxychloride

WP 3g/L @ 2000L/ha 11,2 100 96 37

Pneumatic-

Electrostatic

Mist-blower

Cuprous oxide WG

1g/L @ 750L/ha and

Copper Oxychloride

WP 3g/L @ 750L/ha 3,4 98 96 79

Pneumatic-

Electrostatic

Mist-blower

NanoGreen SC

2.5ml/L @ 750L/ha 6 100 98 29

Pneumatic-

Electrostatic

Mist-blower

NanoGreen SC

10ml/L @750L/ha 6 100 99 3

Unsprayed 0 37 27 100

Figure 1: Copper residues deposition on a leaf collected from the tree sprayed with Pneumatic-

Electrostatic Mist-blower 12g/L @1000L/ha on ‘Fuerte’.

Figure 2: Copper residues deposition on a leaf collected from the tree sprayed with commercial

standard mist blower 3g/L @8200L/ha on ‘Fuerte’.