PO Box 416, Letsitele, 0885 ●Tel/Fax(015) 345-1227/ 1840●

Title: Compare the efficacy of commercial spraying equipment with Electrostatic Spraying System (ESS), when applying standard pesticide and fungicide programmes for controlling citrus pests and diseases

Work conducted by: W van de Pypekamp

Work completed by:LP van Jaarsveld & JJ Serfontein

Ref No:09QR24

Client:I & M Smith (Pty). Limited

Lionel de Roland-Phillips and Rodger A. Dryburg

Crop: Citrus, Delta Valencia

Target Organism: Disease; Guignardiacitricarpa (citrus black spot)

Pests; Aonidiella auranti (citrus red scale), Scirtothrips aurantii (Thrips) and

Planococcus citri (mealybug)

Season:2008/2009

Project Site:Letsitele Valley

Compare the efficacy of commercial spraying equipment with

Electrostatic Spraying System (ESS), when applying standard pesticide and fungicide programmes for controlling citrus pests and diseases.

W van de Pypekamp, LP van Jaarsveld & JJ Serfontein

QMS Agri Science, P.O. Box 416, Letsitele, 0885

E-mail:

Aim

The aim of this project was to determine whether concentration of pesticides and fungicides applied per hectare can be decreased with new generation spraying equipment while maintaining acceptable or improved levels of pest and disease control.

Materials and Methods

The trial was conducted at Maradadi Estates, Letsitele Valley, Limpopo Province on a commercial Valencia orchard, cv. Delta with 830 trees/ha. A general commercial spray programme of Maradadi Estates was sprayed with commercial spraying equipment (Jacto boom-sprayer) and compared with the Electrostatic Spraying System (ESS) for pest and disease control. The trial consisted of 3 programmes and an untreated control, applied on semi commercial scale to approximately 0.5 hectare blocks (approx. 120 trees). The three programmes were the normal commercial application (Jacto) and two different ESS application rates namely ESS at 100% of application rate (ESS100) and 80% of application rate (ESS80) respectively (Table 2). An untreated control was also included. Each treatment was replicated 4 times. Chemicals and active ingredients applied in this trial are depicted in Table 1, with spray programs, dosages and volumes sprayed depicted in Table 2. Efficacy of spray programs were evaluated five times depending on target pest pressure and finally at harvest. Thus the data trees were evaluated a total of six times. Twenty fruit from a randomly selected tree per replicate for each treatment, thus 80 fruits per program were evaluated each time. A total of 480 fruit per treatment programme were, therefore, evaluated during the season. The fruit were evaluated for the presence of thrips, red scale and mealybug. Due to low pest numbers, the accumulative counts were calculated (number of fruit as well as number of pest) and used as a data set. The total accumulative fruits per tree infested and level of infestation per infested fruit (mean number of individuals per total infested fruit) were determined for each target pest.

Table 1. Chemical and active ingredients applied on citrus at Maradadi Estates in the Letsitele Valley, Limpopo Province.

Trade name / Active ingredient / Formulation / Active ingredient
Hunter / Chlorphenapyr / SC / 360 g/ℓ
Nemesis / Pyriproxyfen / EC / 100 g/ℓ
Mineral oil / Medium narrow range / EC / 850 g/ℓ
Agrimec / Abamectin / EC / 200 g/ℓ
Dithane M45 / Mancozeb / WG / 750 g/kg
Trimangol / Maneb / EC / 800 g/ℓ
Flint / Trifloxystrobin / WG / 500 g/kg

Table 2. Spray programs applied on citrus at Maradadi Estates in the Letsitele Valley, Limpopo Province.

Program
number / Program
description / Spray
program / Volume
sprayed per ha / Dosage
(/ 100 ℓ) / Date
applied
1 / Jacto, Commercial / Hunter, Nemesis, M-45 & Oil / 10000 / 30mℓ, 30mℓ, 200g & 300mℓ / 21-Oct
Agrimec & Oil / 10000 / 20mℓ & 300mℓ / 18-Nov
Agrimec, Trimangol, Flint & Oil / 10000 / 20mℓ, 150mℓ, 10g & 300mℓ / 8-Jan
2 / ESS 100 / Hunter, Nemesis, M-45 & Oil / 150 / 1500mℓ, 600mℓ, 10kg & 300mℓ / 21-Oct
Agrimec & Oil / 150 / 1000mℓ & 300mℓ / 18-Nov
Agrimec, Trimangol, Flint & Oil / 150 / 1000mℓ, 7500mℓ, 500g & 800mℓ / 8-Jan
3 / ESS 80 / Hunter, Nemesis, M-45 & Oil / 150 / 1200mℓ, 480mℓ, 8kg & 300mℓ / 21-Oct
Agrimec & Oil / 150 / 800mℓ & 300mℓ / 18-Nov
Agrimec, Trimangol, Flint & Oil / 150 / 800mℓ, 6000mℓ, 500g & 800mℓ / 8-Jan
4 / Untreated Control / - / - / - / -

The citrus black spot evaluation was done on the 11th of August 2009. Redscale, mealybug and thrips evaluations were done on the 15th of December 2008, 9th of January 2009, 6th of February the 6th and 24th of August and finally on the 8th of September, just prior to harvest.

Yields were determined by stripping and weighing all the fruit from a single data tree per replicate from three of the four replicates per treatment on the 8th of September 2009. The harvested fruit was used to determine the fruit size distribution with a commercial rope and roller sizer at a local citrus packhouse.

Statistical analysis

The analysis of variance was performed on the cumulative number of insects found on 20 fruit (replicated on four trees) evaluated six times during the season for each treatment programme. The differences between means were determined with Fisher’s t-test at a 5% level of significance, using Statistica 8.0 by Statsoft Inc. However the statistical data is given in Figures 1-6 as the mean accumulative total of the targeted insect pest per total fruit as well as the mean accumulative infestation level per total fruits.

Results and Discussion

Results of the CBS evaluation prior to harvest indicated that no fruit from the different treatment programs had noteworthy black spot lesions. Thus, the efficacy against CBS infection could not be determined. The average mean accumulative number of pests per 480 fruit as well as the mean accumulative number of fruit infested is shown in figures 1 to 6.

Figure 1. The mean total accumilative number of redscale per 480 citrus fruit

*Values in columns followed by the same alphabetical letter do not differ significantly according Fisher’s t-test (p = 0.05)

Figure 2. The mean accumulative number of fruit infested with red scale

*Values in columns followed by the same alphabetical letter do not differ significantly according Fisher’s t-test (p = 0.05)

The Jacto (Programme 1) and untreated control (Programme 2) programmes did not differ regarding red scale control. Both ESS programmes lowered the numbers of red scale per 480 fruit significantly compared to the other 2 programmes (Fig. 1). The number of fruit infested with red scale was also lower on the ESS treatments (Fig. 2). The ESS 100 programme (Programme 2) gave slightly better control than the ESS 80 programme (Programme 3).

Figure 3. The mean total accumilative number of thrip per 480 citrus fruit

*Values in columns followed by the same alphabetical letter do not differ significantly according Fisher’s t-test (p = 0.05)

Figure 4. The mean accumulative number of fruit infested with thrips

*Values in columns followed by the same alphabetical letter do not differ significantly according Fisher’s t-test (p = 0.05)

Thrip control, based on the accumulative number of thrips per 480 fruit was the best on the ESS 80 (Programme 2) followed by the ESS 100 (Programme 3), the Jacto (Programme 1) and the control (Programme 4) (Fig. 3). Only the ESS 80 (Programme 2) differed significantly from the control, but not from the other programmes. The mean accumulative number of fruit infested with thrip was also higher on the control and Jacto than on the ESS programmes (Fig. 4).

Figure 5. The mean total accumilative number of mealybug per 480 citrus fruit

*Values in columns followed by the same alphabetical letter do not differ significantly according Fisher’s t-test (p = 0.05)

Figure 6. The mean accumulative number of fruit infested with mealybug

*Values in columns followed by the same alphabetical letter do not differ significantly according Fisher’s t-test (p = 0.05)

Mealy bug counts were low during the evaluation period. Accumulative counts were, however, significantly higher on the Jacto (Programme 1) than on the control (Programme 4). The ESS 100 (Programme 2) gave the best control; significantly better than the Jacto (Programme 1) but not than the control (Programme 4) (Fig. 5). The mean accumulative total number of fruit infested with mealybug was also the lowest on the ESS 100 (Programme 2) and the highest on the Jacto (Programme 1) (Fig. 6).

Figure 7. The Average yield obtained per tree for various programs applied on citrus at Maridadi Estate in the Letsitele area, Limpopo Province.*Values in columns followed by the same alphabetical letter do not differ significantly according Fisher’s t-test (p = 0.05)

Figure 8. The yield size distribution of the harvested fruits for various programs applied on citrus at Maridadi Estate in the Letsitele area, Limpopo Province.

The average weight of fruit and the fruit size distribution are given in Figure 7 and Figure 8. The yield and fruit size distribution results obtained in this study are erratic, since no records exists that a plant growth regulator was sprayed in the 2008-2009 growing season. All treatment programmes had, however, a better yield than the untreated control, but not significantly so (Figure 7). No clear trend could be observed in the fruit size distribution between the different treatment programmes (Figure 8).

In this trial, both ESS programmes gave better pest control than the commercial application with the 100% ESS application rate being supperior to the 80% rate on red scale and mealy bug. Thrip control was slightly better on the 80% application than on the 100%.

Unfortunately, no data could be obtained regarding the control of citrus black spot (CBS) as the disease was not detected in the orchard. CBS is regarded as the most important disease on South African citrus due to the phytosanitary restrictions on infected fruit entering the EU. Preventative fungicides are applied at high volumes in the commercial setup to ensure propper fruit coverage and protection. It is therefore important to evaluate the ESS system in a high disease pressure environment.

The supperior efficacy of the ESS application regarding pest control to commercial application in this trial warrents further trials. If equally or more effective, the ESS with it’s low volume application will proof to be extremely cost saving on the long run. According to these results, the ESS does have a place in insect control on citrus. The possibility of the ESS system replacing some, but not all applications, should alo be exploited.