Psa-V Product Testing Field Trial Report. Trial 1: Hort16A (2 December January 2012)

Transcription

1 Psa-V Product Testing Field Trial Report Trial 1: Hort16A (2 December January 2012) 23 January 2012

2 Disclaimer This report has been prepared based on information available at the time of publication which is inherently preliminary in nature and subject to change. No party, including without limitation, Kiwifruit Vine Health Incorporated, Plant & Food Research and ZESPRI Group Limited, makes any warranty, representation or guarantee as to the accuracy and/or completeness of the information regarding Psa, potential treatments and/or best treatment practice, and none of those parties shall be liable to any person for any loss arising from that person s reliance on the information and/or for any damages arising out of or connected with the use of the enclosed information. No obligation is accepted or undertaken to update this or any other information or publicly release revisions to this document to reflect additional information, circumstances or changes in expectations which occur after the date of this document. 2

3 Introduction ZESPRI is coordinating the screening of the effectiveness of a wide range of products to control the virulent type of Pseudomonas syringae pv. actinidiae (Psa-V). The screening programme has been developed to identify, rigorously test and then get permission to use suitable products as part of the crop protection programme (CPP) to help manage Psa-V. To understand the steps in the product testing programme the process is outlined below. The final stage in the testing programme is field testing which is the subject of this report. The efficacy of products for the control of Psa-V is being evaluated using potted plants on an orchard in Te Puke already infected with Psa-V. The plants have been propagated Psa-V free and are treated with products prior to being shifted to the trial site where they are inoculated with Psa-V 1. Symptoms in the form of leaf spot development are subsequently monitored in the field. Products are applied using protocols agreed with the suppliers. ZESPRI has contracted HortEvaluation Ltd, led by Lynda Hawes, to undertake the field trials. The results are reported directly to ZESPRI so that publications of this nature can be produced. 1 Consent has been obtained from MAF, ZIL, KVH and immediate orcharding neighbours for inoculation. 3

4 Methodology Plants Hort16A female plants were used. These were 2 year old on 1 year old Bruno rootstocks, sourced from Pyes Pa (Tauranga) in September These were kept at a greenhouse facility in Rotorua to advance growth until needed. The plants were believed to be Psa-free at the start of the trial as no symptoms were observed previously. Although not a guarantee that the plants were clean, Psa was not detected in leaf samples taken previously in October. At the time of laying out the trial, the plants were approximately 2m in height with a significant number of leaves (Figure 1). Figure 1. Hort16A plants used in first trial (approx. 2m tall). Treatments Table 1 lists the treatments which were each applied to 20 plants (single plant replicates) prior to inoculation (beginning 2 December 2011). Rates and timing were provided by suppliers. Plants were then inoculated in the field using 10 6 cfu/ml of Psa-V then laid out randomly in the trial block. Following inoculation, plants were watered from above for 48 hours using 2L/hr drip irrigation to maximise infection. 4

5 Table 1. List of treatments applied. Products Active Ingredients Rates Application timing and frequency Actigard 1,2,3- benzothiadiazole-7- thiocarboxylic acids-methyl-ester 200g/ha Once 7 days before inoculation BioAlexin Plant extracts 300ml/100L Once 7 days before and once 1 day after inoculation Hydrogen peroxide (35% w/w) Hydrogen peroxide 430ml/100L (equates to 1500ppm) Once 7 days before inoculation Phyton 27 Copper sulphate 300ml/100L Once 1 day before inoculation Serenade Max Bacillus subtilis 350g/100L Serenade MAX + 35ml/100L Du-Wett Once 12 hours before inoculation Kocide Opti Copper hydroxide 90g/100L Kocide Opti + 20ml/100L Latron Champ DP Copper hydroxide 75g/100L Champ DP + 0.1% Driftstop Once 1 day before inoculation Once 1 day before inoculation Liquicop Copper ammonium acetate 500mL/100L Liquicop + 50mL/100L Biofilm Once 1 day before inoculation Nordox 75 WG (summer rate) Nordox 75 WG (below summer rate) Copper oxide 37.5g/100L Once 1 day before inoculation Copper oxide 25g/100L Once 1 day before inoculation KeyStrepto Streptomycin 60g/100L Once 1 day before inoculation Agriphage - preventative Agriphage curative Water:Water Water:PSA 10 8 (1:100 dilution) Once 1 day before inoculation then weekly after inoculation for 4 weeks 10 8 (1:100 dilution) After inoculation, twice-weekly for 4 weeks On the day On the day 5

6 Treatment application and inoculation Treatments were applied to Psa-free potted plants in a greenhouse facility in Rotorua prior to shifting of plants to the field trial site in Te Puke for inoculation. A gas powered backpack sprayer was used to produce fine droplets. The entire canopy of each plant was sprayed to wet with leaves covered thoroughly. Where required, product application rates were adjusted to compensate for the smaller volumes of canopy being treated. Inoculation, which MAF permission was obtained for, was undertaken at the trial site inside a temporary spray booth to minimise the spread of inoculum. Plant and Food Research staff from Ruakura provided fresh inoculum on the day and sprayed the inoculum onto plants using 5L multi-purpose hand-held pressure sprayers with fine nozzle. The undersides of leaves were sprayed to wet. This lower leaf environment is more conducive to Psa infection. Samples of the Psa-V applied were collected throughout the day to check it remained at a strength of 10 6 cfu/ml throughout. Subsequent lab analyses confirmed this occurred. Assessments Four assessments were carried out on an approximately weekly basis after inoculation i.e. December 16 th (+8 days), 22 nd (+15 days), 29 th (+22 days) and January 5 th (+29 days). As the plants were so large, the percentage of total leaf area per plant covered in Psa-V leaf spotting was visually estimated at each assessment time. At the 2 nd assessment, 15 days after inoculation, the degree of phytotoxicity was scored visually using the following scale: 0 = none 1 = light 2 = moderate 3 = severe Phytotoxicity scoring was based on the severity of the following symptoms: darkening of leaf veins on underside of leaves, bronzing and speckling of leaf surface, and yellowing of leaves. While the measurements were subjective, the same assessor performed each assessment to ensure consistency of scoring. Throughout treatment application, inoculation and assessment, the focus was on ensuring consistency across treatments. Weather Weather conditions during field trials need consideration when interpreting results hence a summary is presented here. The first experiment was characterised by significant amounts of rain. i) Weather in Rotorua between application of treatments and transfer of plants to trial site for inoculation (based on Metservice website information). Appendix 1. 6

7 In the 7 days following application of the elicitors (Actigard, BioAlexin and Hydrogen Peroxide) approximately 50mm of rain fell as the plants rested outside. A small amount of rain fell after Blossom Bless and Phyton 27 was applied (2 days before inoculation) and none after the protectants were applied (1 day before inoculation). After the application of treatments, plants were returned outside prior to being transferred to the trial site. If it was raining when treatments were due to be applied, application was done indoors with the plants being allowed to dry fully before being shifted outdoors later in the day. Plants were also dry when products were applied. ii) Weather in the field between inoculation and the final 4 th week assessment at field trial site in Te Puke (based on installed Harvest.com weather station). Appendix 2. - To maximise infection, vines were drip irrigated from above following inoculation for 48 hours - Significant rainfall occurred in the first week after inoculation, particularly on December 15 (approx. 115mm), a day before the first assessment - Some rain fell between 1 st and 2 nd assessments (approx. 70mm) - Relatively dry between 2 nd and 3 rd assessments (approx. 10mm) - Major rainfall occurred between 3 rd and 4 th assessments (approx. 280mm) Average daily temperature increased steadily from the 1 st assessment i.e. December 16. Results Leaf spotting The following graphs show the amount of leaf spotting associated with each treatment. Generally there was an increase in leaf spotting over time across treatments. The plants that were not inoculated (Water:Water) developed leaf spotting presumably as a result of inoculum present at the trial site. Some secondary symptoms (shoot dieback) were observed although this may have been the result of the plants being wounded throughout the trial. Figure 2 shows the amount of leaf spotting relative to that found in the Psa-V control treatment each time. A value of 1 means the treatment had the same level of leaf spotting as the Water:Psa control (and therefore did not reduce leaf spotting). A value of less than 1 means a treatment had less spotting than the Water:Psa control (i.e. reduced leaf spotting) while a value of 1 means the treatment had more leaf spotting (i.e. increased leaf spotting). Figure 3 shows the absolute amounts of leaf spotting found i.e. percent of leaf area covered in spots. As the assessments are visual and subjective, there may be some inconsistencies in absolute values between times. Figure 2 removes some of this variation. The treatment values within each assessment time can be confidently compared. 7

8 Leaf spotting % Leaf spotting % Figure 2. Average amounts of leaf spotting for each treatment relative to the Water:Psa control (i.e. unprotected plants inoculated with Psa-V at 10 6 cfu/ml). +8 days +15 days +22 days +29 days Figure 3. Average percent leaf spotting for each treatment. +8 days +15 days +22 days +29 days Asterisks denote values were significantly lower (P<0.05) than the Water:Psa control values at the same assessment time (according to a Wilcoxon test). Error bars are standard error bars. At each assessment time, none of the treatments had significantly less leaf spotting than the Water:Water controls. 8

9 Phytotoxicity score Phytotoxicity Low levels of phytotoxicity were observed on all the copper treatments (Figure 4). The highest amount of phytotoxicity was observed for the Liquicop and Phyton 27 treatments followed by Nordox and Champ with Kocide Opti having the least. There was no statistical difference between the two Nordox treatments. Figure 4. Average amounts of phytotoxicity for each treatment. Copper treatments with a letter in common above them are not significantly different from each other (according to a Wilcoxon test; P < 0.05) b a ac b ac bc 0.00 Interpretation of results All the copper and KeyStrepto (KS) treatments had a significant knockdown effect on the Psa-V that was applied during inoculation (with little or no difference in efficacy between these treatments). This is based on the observation that leaf spotting was consistently low for these treatments throughout compared to the Water:Psa control. The KS result is consistent with it being thought of as a short-lived/sterilant product. The coppers previously had limited efficacy in greenhouse testing indicating field testing may be a better assay for these. Further trials will clarify this. The results do not provide a clear indication of how long treatments were efficacious for. While the copper and KS treatments appeared to reduce leaf spotting initially, the level of leaf spotting for these treatments thereafter was largely no different to that of the 9

10 Water:Water control (which provided an indication of leaf spotting resulting from Psa-V at the trial site). The elicitors, Actigard and BioAlexin, reduced leaf spotting initially but not in the later weeks. One hypothesis is that these treatments had little or no direct effect on the Psa-V bacteria that was applied during inoculation but that they helped the plant to stave off infection and delay expression of symptoms. Like many of the other treatments, leaf spotting for the Serenade Max treatment initially was lower than that of the Water:Psa control indicating it impacted on the Psa-V that was actively added. However, leaf spotting throughout was no lower than for the Water:Water controls so it is not clear how long this treatment was efficacious for. Significant amounts of rain fell in the first week that plants were in the field particularly on the 15 th of December (approx. 115mm). This may have impacted on the length of time that all treatments were efficacious for and may explain the increase in leaf spotting over time. Rain, a total of 50mm fell during the week between application of the Actigard, BioAlexin and Hydrogen Peroxide and inoculation with the Psa-V (30mm of this fell 2 days after application). The impact of this rain on the efficacy of these products is not expected to be significant given their mode of action. After inoculation, plants were wetted for 48 hours by overhead drip irrigation (to maximise infection). This may have impacted on the efficacy of some treatments. Leaf spotting was evident and not significantly reduced throughout the trial for the hydrogen peroxide (applied just once as an elicitor 7 days prior to inoculation at a rate of 1500ppm) and the Agriphage treatments (applied multiple times). Low levels of phytotoxicity symptoms were visible from just one application of all the copper treatments, bearing in mind young plants were treated. This will be monitored in future trials. 10

11 Summary This initial field trial has provided a relative measure of efficacy of a range of treatments on Hort16A under pressure conditions and in particular, significant amounts of rain. Many of the treatments appeared to knockdown Psa-V or delay infection. However, some appeared to have little or no effect namely Hydrogen Peroxide and Agriphages. None of these treatments (most applied just once) provided lasting suppression of symptoms at least under the conditions of this trial. As most treatments in this trial were applied just once (prior to inoculation), future trials will consider repeat applications of treatments. Phytotoxicity, albeit low levels, was visible from just one application of the coppers so further work on application rates may be required to reduce this. From the results here, it is not clear how long some treatments like the copper ones were efficacious for so further testing is required to clarify this. 11

12 Appendix 1. Rotorua weather, following application of elicitors (on the morning of Dec 2) in Trial 1 with Hort16A. Source: Metservice website. 12

13 Appendix 2. Weather in the field during ZESPRI Field Trial 1. Source: Harvest.com weather station on site. - Average Daily Air Temperature ( C) Average Wind (km/h) Rainfall (mm) Relative Humidity (%) hrs of above vine drip irrigation 1st assessment Dec 16 (just after large rain event) 2nd assessment Dec 22 3rd assessment Dec 29 4th assessment Jan 5 13