testing rainfastness efficacy of sticker modify

Title Authors

vegIMPACT NL Report 2

February 2020

Testing rainfastness efficacy of sticker

Modify

Huub Schepers, Bert Evenhuis and Corina Topper

vegIMPACT Report 2 – Testing rainfastness efficacy of sticker Modify

The vegIMPACT NL program contributes to improved vegetable production and private sector

development in Indonesia. The program builds on the results of previous joint Indonesian-Dutch

horticultural cooperation projects, especially the vegIMPACT program (2012 – 2017). The program

activities of vegIMPACT NL (2017-2020) address Knowledge transfer, Seed potato technology and supply

system, Shallot production and post-harvest technology and Young farmers, while digital information

and social media are cross-cutting and supporting activities. The vegIMPACT NL program is financed by

the Government of the Netherlands and coordinated by Wageningen University & Research in The

Netherlands.

Wageningen University & Research

Contact person: Huib Hengsdijk, [email protected]

© 2018 Wageningen University & Research, Wageningen Plant Research, P.O. Box 16, 6700 AA

Wageningen, The Netherlands; T +31 (0)317 48 07 00; www.wur.nl/plant-research .

Stichting Wageningen Research. All rights reserved. No part of this publication may be reproduced, stored in

an automated database, or transmitted, in any form or by any means, whether electronically, mechanically,

through photocopying, recording or otherwise, without the prior written consent of Stichting Wageningen

Research.

DLO is not liable for any adverse consequences resulting from the use of data from this publication.

mailto:[email protected]

http://www.wur.nl/plant-research


Testing rainfastness efficacy of sticker Modify

Huub Schepers, Bert Evenhuis and Corina Topper


Table of Contents

1. Introduction .......................................................................................................................................... 5

2. Materials and methods ........................................................................................................................ 5

2.1 Potato pot trial lay-out ....................................................................................................................... 5

2.2 Onion pot trial lay-out ........................................................................................................................ 6

2.3 Statistical analyses .............................................................................................................................. 7

3. Results .................................................................................................................................................. 8

3.1 Potato ................................................................................................................................................. 8

3.2 Onion ................................................................................................................................................ 10

4. Discussion and conclusions ................................................................................................................ 12

5. References .......................................................................................................................................... 14

5


1. Introduction

Adjuvants are substances without significant agrochemical properties which can increase the efficacy of a plant protection product when tank-mixed with that product. Adjuvants can enhance the efficacy by changing the physical, chemical, or biological properties of the plant protection product. In Indonesia, late blight (Phytophthora infestans) is a destructive disease in potato (Solanum tuberosum) that can destroy a complete crop. Similarly, in shallots (Allium cepa L. Aggregatum group), anthracnose (Colletotrichum gloeosporioides) and downy mildew (Peronospora destructor) are important diseases that can cause high yield losses. Therefore, Indonesian farmers frequently spray mancozeb-based fungicides to prevent infection with these diseases. Farmers use adjuvants to improve the rainfastness of mancozeb and the spreading of spray droplets on the crops. Effects of locally available stickers proved to be only partially effective compared to the specialized sticker product Bond (Schepers et al., 2014, 2016; De Putter et al., 2016). The Dutch company Modify has the specialized ‘super-sticker Fullstop®’ in its portfolio and is willing to bring this to the market in Indonesia. This study was carried out to investigate the influence of Fullstop and the adjuvant Agristick -which is used in Indonesia- on the deposition of mancozeb on potato and onion in pot experiments in the glasshouse of Wageningen University & Research in Lelystad, the Netherlands.

2. Materials and methods

2.1 Potato pot trial lay-out

Potatoes cv. Bintje were planted, one tuber per pot filled with standard potting soil, on 16 May 2018 and grown at ambient temperature in a glasshouse in Lelystad, the Netherlands. The potato plants were sprayed on 7 June 2018. Per treatment 4 pots were used. The fungicide Tridex® 75 DG (75% mancozeb) from UPL Benelux BV was used at 2 kg/ha. The adjuvant Agristick® (alkilaril polyglycolether 400 g/l) from BayerCropScience was used at 0.05% v/v. The adjuvant Fullstop® was kindly provided by Modify and used at 0.1% v/v. Fullstop® is not available in Indonesia but was used as a reference since this product has proven sticker characteristics (www.modify.nl ). The fungicides were sprayed in a spray cabin using a spray boom with three TeeJet 110.04 spray nozzles, placed 50 cm apart and 50 cm above mean plant height. The spray volume used was 250 L/ha. At 0.5 and 3 hours after spraying, the plants were exposed to a very heavy rain event (120 mm/h applied for a total of 15 min, providing 30 mm total rain). Rain was simulated using a spray boom with TeeJet 110.08 nozzles. On 12 June 2018, 4 leaves per pot were picked for mancozeb residue analysis. The leaf samples from each of two pots per treatment were combined to create duplicate samples. Samples were analysed with Headspace GCMS method by TLR International laboratories, Rotterdam, the Netherlands. Inoculation was carried out with P. infestans on air dry plants on 12 June 2018. Plants were incubated at a high relative humidity (>98%) for 18 hours. Four and six days after inoculation, the percentage plant surface infected with P. infestans was assessed (Cruickshank et al., 1982). Since spray intervals in practice are on average five days, the sampling and inoculation took place five days after spraying thus testing the influence of the factors studied on the protection level (mancozeb residue, biological efficacy) at the end of a spray interval.

http://www.modify.nl/

6


Table 1. Treatments used in the potato experiment

Period between spraying and rain simulation (hour)

Treatment Dose rate 0.5 3 Pre-rain

Untreated control - x x

Tridex® 2 kg/ha x x x

Tridex® + Agristick® 2 kg/ha +0,05% x x x

Tridex® + Fullstop® 2 kg/ha + 0,1% x x x

Agristick® 0.05% x

Fullstop® 0.1% x

2.2 Onion pot trial lay-out

The common onion (Alium cepa) was selected for the pot experiment since this crop is easier to grow in the Netherlands than shallots, but still has a similar waxy leaf structure to shallots. Onions cv. Hoza were sown in pots filled with potting soil mixed with sand and clay on 27 June 2018 and grown at ambient temperature in a glasshouse in Lelystad, the Netherlands. The onion plants were sprayed on 27 July 2018. Per treatment 4 pots were used. The fungicide, adjuvants, spray technique and rain simulation used were identical to potato, except for the spray volume used which was 150 L/ha. On 1 August 2018 just before the inoculation with P. destructor leaf samples were collected for mancozeb residue analysis by taking 6 leaves per pot. The leaf samples from each of two pots per treatment were combined to create duplicate samples. Inoculation was carried out with P. destructor on 1 August 2018. Plants were placed at high relative humidity (> 98%) for one night. Per pot the number of infected leaves with downy mildew was counted on 16, 17, 22 and 24 August 2018. Since spray intervals in practice are on average five days, the sampling and inoculation took place five days after spraying thus testing the influence of the factors studied on the protection level (mancozeb residue, biological efficacy) at the end of a spraying interval.

Table 2. Treatments used in the onion experiment

Period between spraying and rain simulation (hour)

Treatment Dose rate 0.5 3 Pre-rain

Untreated control - x x

Tridex® 2 kg/ha x x x

Tridex® + Agristick® 2 kg/ha +0,05% x x x

Tridex® + Fullstop® 2 kg/ha + 0,1% x x x

Agristick® 0.05% x

Fullstop® 0.1% x

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2.3 Statistical analyses

Analysis of variance on the percentage necrotic potato foliage and number of infected onion leaves was made using GENSTAT 19th Edition. The experiments were carried out with four replications. Each replication consisted of one pot which was one plant for potato and 5 plants for onion. Transformation of data was carried out when necessary.

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3. Results

3.1 Potato

The amount of mancozeb measured on the leaf samples of the different treatments is presented in Table 3. Pre-rain, neither the addition of Agristick nor Fullstop influenced the level of residue compared to Tridex alone. Pre-rain, adding Agristick resulted in a higher level of residue compared to adding Fullstop, but this difference was statistically not significant. The pre-rain residues quantify the spray retention and ability of the adjuvants to enhance retention. Rain clearly reduced the residue level. The reduction was more pronounced when time between application and rain was 0.5 hour compared to 3 hours. Tank-mixing Tridex with Agristick and Fullstop did not result in a higher level of mancozeb residue compared to Tridex alone: in other words, both adjuvants did not increase the rainfastness of mancozeb.

Table 3. Effect of adjuvants and rain simulation on mancozeb residue (ppm) on potato leaves in the

potato pot experiment.

Period between spraying and rain simulation (hour) Treatment 0.5 3 Pre-rain Mean

Untreated control -1) -1) 0 a 0 Tridex® 19.95 ab3 38.35 bcd 47.80 cd 35.37

Tridex® + Agristick® 22.30 abc 31.75 bc 60.30 d 38.12 Tridex® + Fullstop® 23.65 abc 29.10 bc 44.05 bcd 32.27

Mean2) 21.97 33.07 50.72

1) not tested 2) excluding untreated control. 3) LSD = 13.01. Values followed by the same letter are not significantly different (p=0.05)

The infected foliage of the potato plants sprayed with the different treatments is presented in Tables 4,

5, 6 and 7. The untreated control was severely infected indicating that the artificial inoculation was

successful.

Pre-rain application of Tridex, Tridex + Agristick and Tridex + Fullstop resulted in similar levels of P.

infestans infection, significantly reducing infection compared to the untreated control. Fullstop and

Agristick alone did not have an effect on the P. infestans infection and resulted in similar infection levels

compared to the untreated control. Rain showers clearly decreased the levels of mancozeb on the

leaves and subsequently increased the level of infection in the treated plants. The increase was more

pronounced when time between application and rain was 0.5 hour compared to 3 hours. Tank-mixing

Tridex with Agristick and Fullstop did not result in a lower level of infection compared to Tridex alone: in

other words, both adjuvants did not increase the rainfastness of mancozeb.

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Table 4. Effect of adjuvant and rain simulation on P. infestans infection (%) on 16 June 2018, 4 days

after inoculation.


Untreated control 60 d4) -1) 65 d 62.5 Tridex® 21.3 bc 17.5 ab 14.3 a 17.7

Tridex® + Agristick® 23.8 c 13.5 a 15.8 a 18.8 Tridex® + Fullstop® 18.3 b 16.8 ab 16.3 ab 17.1

Fullstop® - - 653) Agristick® - - 62.53)

Mean2) 21.1 17.1 15.5 17.9

1) not tested 2) excluding untreated control, Fullstop and Agristick. 3) were not included in the statistical analysis. 4) LSD = 5.5. Values followed by the same letter are not significantly different (p=0.05).


after inoculation.


Untreated control 96.5 e4) -1) 98.8 e 97.7 Tridex® 47.5 c d 41.3 abc 37.5 ab 42.1

Tridex® + Agristick® 47.5 c d 35.0 ab 33.8 a 38.8 Tridex® + Fullstop® 42.5 bcd 38.8 ab 36.3 ab 39.2

Fullstop® - - 97.33) Agristick® - - 95.33)

Mean2) 45.8 38.4 35.9

1) not tested 2) excluding untreated control, Fullstop and Agristick. 3) were not included in the statistical analysis. 4) LSD = 8.5. Values followed by the same letter are not significantly different (p=0.05).

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after inoculation.


Untreated control 99 e4) -1) 100 e 99.5 Tridex® 83.8 cd 83.8 cd 65 b 77.5

Tridex® + Agristick® 85 d 76.3 c 52.5 a 71.3 Tridex® + Fullstop® 80 cd 77.5 c d 57.5 ab 71.7


Mean2) 82.9 79.2 58.3

1) not tested 2) excluding untreated control, Fullstop and Agristick. LSD = 7.7. 3) were not included in the statistical analysis. 4) values followed by the same letter are not significantly different (p=0.05).

Table 7. Effect of adjuvant and rain simulation on P. infestans infection (%), average of 4, 6 and 10 days

after inoculation.


Untreated control 85.2 g4) -1) 87.9 g Tridex® 50.8 ef 47.5 def 38.9 ab

Tridex® + Agristick® 52.1 f 41.6 bc 34.0 a Tridex® + Fullstop® 46.9 de 44.3 cd 36.7 ab


Mean2) 49.9 44.5 36.6

1) not tested 2) excluding untreated control, Fullstop and Agristick. LSD = 5.0. 3) were not included in the statistical analysis. 4) values followed by the same letter are not significantly different (p=0.05).

3.2 Onion

Pre-rain, Tridex applied without adjuvant resulted in mancozeb residues of 0.28 mg/kg (Table 8). Pre-rain application of tank-mixing Tridex with Agristick or Fullstop did not significantly influence the mancozeb residue in comparison to Tridex alone. Rain clearly reduced the mancozeb residue level. The reduction was more pronounced when time between application and rain was 0.5 hour compared to 3 hours. At both rain-timings, tank-mixing Tridex with Agristick and Fullstop did not result in a higher level of residue compared to Tridex alone, i.e. both adjuvants did not increase the rainfastness of mancozeb.

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Table 8. Effect of adjuvant and rain simulation on mancozeb residue (ppm) on onion leaves in the onion

pot experiment.


Untreated control 0 a3) -1) 0 a 0 Tridex® 0 a 0.46 b 0.28 ab 0.25

Tridex® + Agristick® 0.03 ab 0.09 ab 0.33 ab 0.15 Tridex® + Fullstop® 0.07 ab 0.13 ab 0.16 ab 0.12

Mean2) 0.03 0.23 0.26

1) not tested 2) excluding untreated control. LSD = 0.21. 3) values followed by the same letter are not significantly different (p=0.05).

The results of the strategies on the control of P. destructor are presented in Table 9. The artificial inoculation with downy mildew was successful. The untreated control showed on average almost 27% infected leaves. Spraying Tridex® with and without adjuvants did not result in a significant control of downy mildew. The number of infected leaves was lower when rain was applied 3 hours after spraying compared to pre-rain and the 0.5-hour strategy, but this difference was not statistically significant. At all 3 strategies (pre-rain, 0.5 hour and 3 hours) the number of infected leaves was lower in the treatments where Agristick or Fullstop was added to Tridex compared to Tridex alone. However, these differences were not statistically significant.

Table 9. Effect of adjuvant and rain simulation on P. destructor infection (total % infected leaves per

pot) on 24 August 2018, 22 days after inoculation.


Untreated control 30.16 c3) -1) 23.17 abc 26.67 Tridex® 25.89 abc 16.45 abc 25.69 abc 22.68

Tridex® + Agristick® 23.46 abc 11.03 a 10.11 a 14.87 Tridex® + Fullstop® 19.86 abc 13.64 abc 11.64 ab 15.05

Fullstop® - - 29.49 bc 29.49 Agristick® - - 22.60 abc 22.60

Mean2) 24.84 13.71 20.45

1) not tested 2) excluding untreated control. LSD = 9.72. 3) values followed by the same letter are not significantly different (p=0.05).

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4. Discussion and conclusions

This study was carried out to investigate the influence of the sticker Fullstop and the adjuvant Agristick -which is used in Indonesia- on the deposition and rainfastness of mancozeb on potato and onion in pot experiments. The sticker Bond was included in previous experiments (Schepers et al. 2014, 2016; De Putter et al., 2016) but not included in the pot experiments reported here because the company has indicated that it will not become available in Indonesia. In Table 10 the materials & methods and a summary of the results of the 2014 and 2016 experiments are presented. In Table 11 the materials & methods and a summary of the results of the 2018 experiment (this report) are presented. Table 10. Materials & methods of the adjuvant experiments in 2014 and 2016.

Potato 2014 Potato 2016 Onion 2016

Adjuvants Agristick, Indostick, APSA, Acrobatik, Bond

Indostick, Bond Indostick, Bond

Fungicide Mancozeb Flowable Mancozeb DG Mancozeb DG

Spray volume 250 l/ha 250 l/ha 150 l/ha

Spray date 28 May 2 July 16 July

Rain 30 mm/15 minutes 36 mm/15 minutes 36 mm/15 minutes

Mancozeb residue: no rain, 250 l/ha

199 ppm (100%) 100 ppm (100%) 3.7 ppm (100%)

Mancozeb residue: rain1 13 ppm (7 %) 46 ppm (46%) 0.2 ppm (5%)

Mancozeb residue: rain1 + Bond

22.6 ppm (11%) 79 ppm (79%) 3.1 ppm (84%)

Mancozeb residue: rain1 + Indostick

38.9 ppm (20%) 66 ppm (66%) 0.6 ppm (16%)

1 Rain was applied 0.5 hour after spray application in 2014. In 2016, rain was applied 3 hours after spray application

Table 11. Materials & methods of the adjuvant experiments in 2018.

Potato 2018 Onion 2018

Adjuvants Agristick, Fullstop Agristick, Fullstop

Fungicide Mancozeb DG Mancozeb DG

Spray volume 250 l/ha 150 l/ha

Spray date 7 June 27 July

Rain 30 mm/15 minutes 30 mm/15 minutes

Mancozeb residue: no rain, 250 l/ha 47.8 ppm (100%) 0.28 ppm (100%)

Mancozeb residue: rain1 19.95 ppm (42%) 0 ppm (0 %)

Mancozeb residue: rain1 + Fullstop 23.65 ppm (50%) 0.07 ppm (25%)

Mancozeb residue: rain1 + Agristick 22.30 ppm (47%) 0.03 ppm (11%)

1 Rain applied 0.5 hour after spray application

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The rainfastness of mancozeb can be influenced by many factors, such as:

• the formulation of the mancozeb product

• the spray volume

• the rain intensity

• the time between spraying and raining

• the conditions of the potato/onion leaves (wax layer)

• the leaf area index (LAI) of the crop

The differences in the results of experiments can partially be explained by differences in these factors. In 2014, a flowable formulation of mancozeb was used because it was known that such a formulation had a very weak rainfastness in potato compared to the DG (dry granulate) formulation. In 2014, the rain event washed off more than 90% of the mancozeb residue, whereas in 2016 and 2018 when the DG formation was used – because this formulation is frequently used in practice- “only” 54-58% was washed off.

The rain intensity and the spray volume were similar in all experiments.

Although the experiments were carried out in the same period of the season it cannot be excluded that the condition of the wax layer of the potato and onion plants were different between the experiments and could have influenced the results.

In 2016 and 2018 the same DG formulation of mancozeb was used. The residue levels observed in the 2018 experiment were lower compared to the 2016 experiment. In potato the residue level in the treatment without rain was 47.8 ppm compared to 100 ppm in 2016. In onion the differences was clearly larger: 0.28 ppm in 2018 compared to 3.7 ppm in 2016. It is not clear what caused these differences. The formulation, the spray volume, the time of taking the samples and the number of leaves sampled were similar in both experiments.

Taking all experiments into account, several conclusions can be made:

• Intensive rain washes off considerable amounts of mancozeb from potato and onion leaves thus reducing the protection level of the leaves for fungal pathogens;

• The flowable mancozeb formulation of mancozeb has a lower rainfastness compared to the DG (dry granulate) formulation;

• Adjuvants tank mixed with mancozeb do result in higher levels of mancozeb residue on potato and onion leaves compared to mancozeb alone. The degree of this positive effect was variable between the experiments.

• Although Bond and Fullstop are designed as adjuvants with particularly good sticking properties, their positive effect on rainfastness was not always better than the locally available adjuvants such as Agristick and Indostick.

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5. References

Cruickshank, G., Stewart, H.E. & R.L. Wastie (1982). An illustrated assessment key for foliage blight of potatoes. Potato Research 25: 213-214.

De Putter, H., Schepers, H., Topper, C. & B. Evenhuis (2016). Effect of adjuvant and spray volume on mancozeb residue on potato and onion leaves and on Phytophthora infestans in potato and Peronospora destructor in onion. vegIMPACT Report 21, February 2016.

Schepers, H., Evenhuis, B. & C. Topper (2014). Influence of adjuvants on the deposition of mancozeb. vegIMPACT Report 5, December 2014.

Schepers, H., De Putter, H., Topper, C., Adiyoga, W., Gunadi, N. & B. Evenhuis (2016). Effect of adjuvant and spray volume on the rainfastness and biological efficacy of mancozeb in potato and onion. Proceedings International Society of Agricultural Adjuvant (ISAA), Monterey, USA 2016: 147-152.

testing rainfastness efficacy of sticker modify

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