SFF Project Summary
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Latest update
Final report
Updated: 14 April 2008
Project description
This project will develop standardized application guidelines for the application of pesticides to avocado tree canopies, which are tailored to the size of the tree. This will result in improved product efficacy and reduced water use.
Problem/opportunity that the project is addressing
Avocado trees can grow to an immense size creating logistical difficulties in terms of pesticide application. There is great variability in terms of tree size and canopy density and hence the canopy area and volume on a per hectare basis. There are no standard application guidelines for water rates, air volumes, pressure or droplet size, and no method for adjusting these in terms of tree height or canopy volume. Current spray practices are very variable particularly in terms of the water rates used, ranging from 1,500 to more than 5,000 litres per hectare. This leads to large differences in the actual dosage of chemical deposited on a per leaf area basis, with subsequent consequences for product efficacy.
The project has been divided into a set of sequential tasks. Current spray practices will initially be surveyed to establish a baseline for comparing any improvement in spray practices on completion of the project. Avocado canopies of different age classes will be characterized in terms of target area and volume and the litres of spray required to treat a cubic meter of avocado canopy determined for different age classes or size of tree. Superpsreader adjuvants will be used to reduce spray volumes and maximise spray retention. Various pesticide/adjuvant combinations will be screened to optimise coverage on fruit and foliage and eliminate the possibility of phytotoxicity developing with low water rates.
Once the low water volume technique using superspreaders has been experimentally verified using a wide range of chemical/adjuvant combinations then best practice guidelines will be developed from both first principles and experimental verification. This will include practical demonstrations characterizing coverage achieved with industry average practice, as determined from the initial survey, compared with best practice determined form this study.
Latest update
The trials comparing high volume application with 3x and 5x concentrate sprays with two different rates of adjuvant (supplied by Elliott Technologies) have been completed. The results show that reducing spray volumes with the addition of the adjuvant increased spray deposits on the outer tree canopy in both the upper and lower canopy sections. Total spray deposits on both leaves and fruit were increased compared to high volume (dilute) sprays. In addition, the evenness of spray coverage on leaf and fruit surfaces was improved. Deposits from a 3-fold reduction in spray application volume were higher than for a 5-fold reduction, due to the large canopy volume of the trees. The addition of a low adjuvant rate was more beneficial overall than a higher rate.
Season long grower trials utilizing large blocks to compare the efficacy of the 3X concentrate plus adjuvant prescriptions relative to high volume dilute applications have been initiated on three orchards (Tauranga, KatiKati and Whangarei) and will run through to March 2008. Efficacy will be evaluated based on packout rates and library tray assessments of fruit quality.
A set of recommended best practice guidelines are being produced from the combined results of the survey and deposit tests. These will be presented to the industry at the 2007 conference and will be published subsequently.
A poster on the use of adjuvant technology to improve the distribution of copper sprays in avocado canopies has been prepared for presentation at the 8th International Symposium of Adjuvants for Agrochemicals to be held in the USA in August.
Update
A series of deposit tests were conducted using 3X and 5X concentrate spray applications with the addition of a spray adjuvant to improve spray retention, enhance wetting of leaf undersides and improve spray coverage. Concentrate spraying utilizes reduced spray application volumes, while maintaining equivalent chemical application rates.
These trials were conducted on four different canopies in total (representing a range of large and medium sized trees) from two different orchards. This work confirmed that the most reliable deposit improvements can be achieved using a 3X concentrate + adjuvant prescription. Higher concentrations are less feasible given the current constraints of the sprayers typically used in the industry, namely airblast sprayers fitted with single sided volutes with gun nozzles to spray into the tops of large trees.
A shift to concentrate spraying will require some modifications to industry spray diary recording practices to ensure that actual chemical application rates (and hence potential residues on fruit) are not confused between conventional high volume and 3X concentrate applications. These changes will put in place as part of the final extension of the technology to industry after the grower “use in practice” trials have been completed (scheduled completion March 2008).
Bill May and David Manktelow completed visits to assess current application practices in relation to different canopies on orchards in Northland, Whangarei and the Bay of Plenty. This work confirmed the often extreme range of tree sizes found within individual orchard blocks and the often inappropriately high or low chemical application rates and spray volumes applied to trees. The variability in application rates arises from a combination of tree size and density variations and in variations in grower application practices, especially driving patterns. There are often significant improvements in chemical use efficiency and reductions in environmental agrichemical burden that could be achieved through simple changes to application practices. This survey also highlighted the variability between sprayers used in the industry and some simple adjustments that could significantly improve machine use efficiency
March 2007 update
Study results to date were summarised and presented to a growers’ conference in June. The survey of growers’ spray application practices in the BOP and Northland has been completed and the results will be published in the AvoScene magazine.
Field studies to confirm formulation and application prescriptions for concentrate sprays, to optimise spray deposits on fruit and foliage, were undertaken from July onwards. The studies confirmed that three times concentrate sprays, plus adjuvant, gave higher spray deposits than dilute sprays. The 3x concentrate spray was more effective (with higher and more even deposits throughout the tree canopy) than 5x concentrate, delivered by conventional airblast sprayers. Adjuvant rates were confirmed, which maximise quantity and evenness of spray deposits, and minimise the cost for growers. The application prescriptions refined in these studies are for 60% of concentrate sprays to be directed to the top third of the tree through Masotti nozzles. To achieve good spray effectiveness and efficiency, sprayers must be accurately calibrated. In addition, it was determined that spray deposits in the upper third of larger trees (i.e. > 6 m) can be increased by approximately 20% if sprayers stand-off trees by 1 m more than conventionally done. This simple technique should improve control of leafroller in tree tops when using airblast sprayers.
Best practice prescriptions for concentrate spray applications have been confirmed for testing against standard spraying practices in selected commercial orchards, commencing January 2007. Candidate orchards are currently being identified in the BOP and Northland.
June 2006
A second well-attended industry field day was held in Whangarei in April (80+ attendees), showing growers how to set up their sprayers to get the best performance from them, and how adjuvant technology can be used to modify the application volumes required for good pest and disease control. The high level of interest by growers and spray contractors in this project resulted in an invitation to present the study results to the Apata Growers’ conference in June. The survey measuring growers’ spray application practices has been completed in the BOP and Northland. Results will be published in the AvoScene magazine in the second half of 2006.
The study on seasonal surface characterisation of fruit and foliage has been completed. The results indicate that at any given time avocado canopies consistent of a range of target surfaces which differ markedly in their degree of water repellency. These results highlight the benefit to be gained through appropriate use of adjuvants.
Laboratory screening for compatibility of all pesticide formulations used on avocados and selected adjuvants has been completed. This study indicates that there some of the pesticides were antagnostic to the adjuvant, but that this could be compensated for through use of a higher concentration of the adjuvant.
Field trials are currently underway in the BOP to refine airblast sprayer setups and adjuvant prescriptions to improve spray deposits on target trees. Best practice prescriptions for concentrate spray applications will be available to test in selected commercial orchards on completion of this field trial study.
December 2005
A hands-on survey measuring growers’ spray application practices has been initiated, to back up the postal survey of growers undertaken earlier this year. The survey consists of on-property examinations of sprayer outputs, output distribution and air output distributions in relation to chemical rates applied to different sized canopies. The immediate finding is that there is no consistency in sprayer setups across the industry and that there is large potential to reduce copper use, especially on smaller tree canopies.
This finding reinforces the results obtained in the parallel study to characterise deposits on trees from existing spray practices. There are large variations in deposits over the four different ground sprayers examined. Small trees (< 7 years old) are receiving the highest spray deposits and appear to be consistently overdosed. Large trees (>15 years old) are often seriously under-dosed, especially in the upper canopy and particularly when sprays are delivered from rigs set up for kiwifruit spraying. Measurements of deposits on large trees resulting from aerial application are still to be measured. Completion of this, and the on-property grower survey, is expected in January.
An article summarizing the results of the spray trails has been prepared for the avocado industry magazine Avoscene and will appear in the March 2006 edition. An industry field day to deliver the results to growers is scheduled for April 2006.
The surface characterisation of fruit and foliage has been underway for four months and will continue for a full year. The laboratory study to determine how spray adjuvants can be used to improve the efficacy of agrochemical sprays on avocados is completed, and information from this will be incorporated in the field trials scheduled to commence in April 2006.
September 2005
The characterisation of spray deposits from existing spray practices is still underway. Completion of this milestone has been hampered by unsettled weather and unavailability of contractors due to priority being given to Hicane applications on kiwifruit. The results of the completed spray trails indicate that smaller trees (<7 years old) receive highest spray deposits. Trees of medium size, and greatest density, (9-12 years) have proven the hardest targets; spray deposits are low, on the inner tree zone particularly, and unevenly distributed throughout the canopy. Large trees (>15 years old) are usually characterised by a relatively open interior with an outer shell of leaves and fruit. They can be very efficiently and evenly sprayed with a well-calibrated airblast sprayer but their coverage is compromised most with poor spray delivery. Fruit and foliage in the inner canopy of all trees received, on average, less than half the spray deposits achieved on outer canopies. An industry field day will be scheduled when this study is completed.
Formulation studies have commenced with the surface characterisation of fruit and foliage. This will identify any seasonal changes in plant surfaces that may compromise spray deposition and retention on avocados, and assist in prescribing adjuvants to overcome these effects. A laboratory study, to measure how adjuvants can improve the surface coverage of agrochemical sprays used on avocados, is underway and results will be used to recommend adjuvants for orchard spray trials in the coming season.
June 2005
Following on from the questionnaire sent out to gather information on spraying practices, the characterisation of spray deposits from existing spray practices is currently underway in BOP orchards. We are measuring spray deposits from five different representative sprayers, including contractor and grower ground-based rigs and an aerial contractor. Three sizes of tree are sprayed by each rig (approx. 5, 8 and 15+ years old) and deposits on fruit and foliage in six canopy zones on each tree size are quantified. The trees are been sprayed with a mixture of copper and a food grade dye (tartrazine). Spray deposits within each zone are being determined. Samples are collected in to plastic bags and transferred back to the laboratory where the dye is washed off and quantified by spectrophotometer. The overall results indicate the relative quantities of spray captured on fruit and foliage in the six different zones within each tree size. At the completion of each trial the sprayer is calibrated to allow accurate estimates of sprayer outputs. Once the results have been analyzed an industry field day will be held highlighting some of the findings with a practical demonstration using a commercial spray contractor and a spray marker.
March 2005
Registered export avocado growers were surveyed on pesticide application methods. The response rate (42%) was very pleasing with 260 completed questionnaires received. A wide cross section of growers completed the survey with orchard size ranging from 8 to 7710 trees with an average of 430 trees. In terms of responsibility for pesticide applications 35% of respondents indicated that they were responsible for all applications, with a further 17% responsible for some. Responsibility for spray applications was left to a third party by 47% of respondents. Ground based spraying was used exclusively by 81% of respondents. AvoGreen uptake amongst respondents was high (57%). Of those that used AvoGreen, 59% programmed sprays on the basis of pest pressure alone with only 5% based solely on calendar spraying.
When it came to spray recommendations, 44% of growers made their own recommendations, with a further 23% doing so in combination with their contractor, monitor or consultant. Those that left it to a third party were most likely to turn to their consultant. When it came to recording spray applications there was a fairly even split between the web version (47%) and the paper version (53%).
The products that growers were most likely to apply themselves were herbicides (78%), foliar fertilizers (69%), insecticides (60%) and fungicides (57%). Many respondents (22%) indicated that they only applied herbicides. Correspondingly, contractors were least likely to apply herbicides (9%) and most likely to apply insecticides (91%) followed by fungicides (84%) and foliar fertilizers (60%).
In terms of equipment, 67% used an air-assisted sprayer with most of these (86%) being airblast sprayers. Most use a volute with 78% using a single sided volute and 6% a double sided volute. Most respondents (86%) sprayed to runoff with an average pressure of 310 psi. Only 19% used a flow meter. Average speeds decreased slightly with tree age from 3.7 km/hr on small trees to 3.3 km/hr on large trees. One respondent applied sprays at 15 km/hr. The same spray pattern tended to be used regardless of tree age (around 60%) and this was to spray trees from two sides i.e. up one row and down the next.
When applying copper sprays water volumes averaged 1390 l/ha on small trees and increased to 2400 l/ha on large trees. Half of the respondents (48%) changed volumes according to the chemical being sprayed. Sprays were considered to reach the top of the trees by 90% of growers. The average interval between calibrations was 14 months, with some giving rarely or never as a response. Growers tended to do any calibration themselves (64%). Of these, 57 % were interested in having a calibration check on their sprayer. There was good support (70%) for holding a field day on spray application techniques, with 49% interested in a calibration/ spray application course.
December 2004
The project steering group have met and agreed to their Terms of Reference which tasks them with ensuring that the project milestones are met on a timely basis and the project delivers results which are of relevance to the avocado industry.
The project is generating considerable interest within the avocado industry with two other parties now wanting to partake in the project. The steering group also agreed that a representative of Environment BOP should be invited to attend a meeting of the steering group at least once per year.
The analysis of the spray dairies is now complete. Data collected in the industry electronic spray diary implemented for the last two seasons has been extracted into a database. Over 100 diaries from the 2003 season and approximately 250 diaries from the 2004 season have been analysed. Copper is the most common chemical applied with chlorpyrifos being the most predominant insecticide. A breakdown was also provided as to which pesticides were most often combined in a single application. The most common combination was copper with either Attack or Averte.
The research contract between PPCNZ and the AIC formalizing the research protocols used in this project has been agreed to and signed. Contracts have also been signed with Elliot Technologies and Avo-Plus formalizing their financial and in-kind support to the project.
A draft of the grower survey form was discussed by the steering group and several questions were revised or added to the survey form as a result. As an incentive for growers to complete the question 20 of the respondents will be selected to have a free calibration check on their sprayer. In addition the AIC will contribute 10 free grower export registrations to be drawn at random from the respondents that have replied by the cut off date.
