Valuable insights shared at APAL Technical Symposium

Published on August 16, 2023

News

Keen to challenge their thinking on orchard management techniques, growers gathered in the Goulburn Valley to find out the latest in best-practice orchard management. 

Agronomists, researchers and technical experts in the apple and pear industry led the speaker sessions on day one of the APAL Technical Symposium, which was held in the Goulburn Valley from 9 to 11 August. 

Highlights of the educational program included new research on managing light in narrow orchard systems, taking a life cycle approach to fighting Alternaria and minimising apple scab fungicide resistance, insights into soil preparation, drainage and management, and exploring how the majority of Australian producers may be able to reduce reliance upon a single introduced – and increasingly vulnerable – bee species.  

Managing light in orchard systems 

Over the past century, a greater understanding of the importance of managing light in orchard systems has brought a transformation in productivity. Dr Ken Breen, Science Team Leader – Temperate Tree Physiology at Plant and Food Research, New Zealand, has been working on understanding the responses of deciduous tree crops and new planar orchard systems and how these may be manipulated to horticultural advantage.  

Photosynthesis (light) is the basic function regulating crop productivity. In other words, yield = orchard light interception + canopy light penetration. Current best-practice Royal Gala orchards are intercepting 55 per cent to 60 per cent of light on average, but utilising precision canopy management (PCM) to dial up light interception to as high as 80 per cent has the potential to lead to a massive improvement in yield. 

Ken described a case study where reducing branch density by approximately one-third and bud numbers by more than half at an orchard in Hawke’s Bay saw fruit weight climb from 150g to 185g while yield increased from 100 to 130 tonnes per hectare. 

Plant and Food Research’s studies suggest a porous and 2D planar cordon system with row spacings of 1.5m or 2m with 10 to 12 upright fruiting stems and 3m between trees is ideal. From the point of view of production potential, wide rows designed around vehicle access and light penetration are wasteful of available solar energy. However, bringing row spacing in would require platforms, sprayers and other equipment suited for narrow rows, but Ken said these were becoming commercially available.  

Key message: As an industry, can we change canopy design to increase orchard light interception to greater than 80 per cent while retaining light penetration to around 25 per cent to 30 per cent of the canopy? If we are going to adopt PCM, we need to come at it with as few preconceived ideas as possible. Everything needs to be on the table, including changing our equipment.  

A better-informed approach to Alternaria disease  

A better understanding of the life cycle of the fungal pathogen Alternaria will help growers manage it more effectively. Caused by multiple Alternaria species, the disease affects high-valued cultivars around the world, with leaf blotch capable of causing over 60 per cent defoliation and fruit spot leading to fruit losses as high as 20 per cent.  

Associate Professor Femi Akinsanmi from the Centre for Horticultural Science, Queensland Alliance for Agriculture and Food Innovation, University of Queensland, took delegates through the sources, timing, disease development and life cycle of Alternaria leaf blotch and fruit spot to enable an informed approach to managing the disease. 

 

• Sources of inoculum: Besides airborne conidia (spores),  the primary source of Alternaria is leaf residue, followed by buds and twigs, then leaves to fruit. Once the disease is present in your orchard it tends to build up over time. 
• Timing of infection: Leaf blotch symptoms appear 20 to 40 days after bloom and will increase over time until fruit spot symptoms appear around 110 to 120 days after bloom. Premature defoliation occurs from 120 days after bloom. New leaf flush is more susceptible than older leaves.  
• Disease development: As leaf litter is the major source of spores, the infection spreads from the base of the canopy. Knowing this will help growers know where to look when monitoring for early signs of infection.  
• Life cycle and weather: Alternaria overwinters in leaf residue before getting into the canopy when splashed with rain. Expect higher occurrence in cool, wetter spring and summer weather.  

Femi recommended good sanitation practices to reduce the source of the spores, along with careful monitoring and chemical applications.  

Key message: Reduce inoculum potential by destroying crop residues (burying, mulching and sweeping). Reduce the rate of spread by improving crop health through nutrition management and irrigation practices. Choose a fungicide group effective for hitting multiple pathogens including Alternaria, and plan your applications around risk periods.    

Apple scab fungicide resistance 

Apple scab/black spot (Venturia inaequalis) is considered high risk for the development of resistance to certain groups of fungicides. DPIRD (Western Australia) Plant Pathologist Dr Andrew Taylor took attendees through the dangers of this situation, how resistance develops, and the research currently underway.  

Venturia inaequalis is listed in the top ten fungi of all species globally for the development of fungicide resistance against single-site (targeted) fungicide groups, including Group 3 and Group 11. At the same time, popular cultivars including Cripps Pink (marketed domestically as Pink Lady) and Cripps Red (marketed domestically as Sundowner®) are highly susceptible to the disease.  

“We’re growing highly susceptible hosts with a pathogen prone to developing resistance,” Andrew said. He stressed that resistance certainly exists in Australia, although little has been published on this subject since 2003.  

Development of resistance depends on the fungicide mode of action. Key mistakes include not following the CropLife Australia guidelines (www.croplife.org.au/resources/programs/resistance-management/apples-pears-apple-and-pear-scab-2-draft__trashed/apple-pear-apple-and-pear-scab/), inadequate spray coverage or incorrect spray timing (often linked to poor sprayer maintenance and calibration), use of protectant products on established infections, incorrect concentrations such as underdosing, and misreading the weather. Loss of efficacy of one single-site group leads to increased pressure on the remaining groups to be effective.  

As part of the CRC SAAFE project (www.crcsaafe.com.au), Andrew’s team is assessing fungicide resistance in the scab population in Australia, undertaking spore trapping in WA orchards and validating disease models, and screening WA apple germplasm for scab-resistant genes with the goal of introducing scab resistance into the breeding program. One of the project’s outcomes will be a scab resistance dashboard to assist growers.  

Key message: Apple black spot is a disease with a relatively high risk of developing resistance to fungicides. Monitoring through a new CRC SAAFE project led by Dr Andrew Taylor will assess isolates from across the country to establish if, to what and where resistance may be emerging.  

Soil preparation, drainage and management 

As an Environmental and Agricultural Soil Scientist with South East Soil & Water, Christian Bannan has gained a keen sense for what causes problem soils.  

“It nearly always comes down to poor land preparation, a lack of information and a failure to do research or due diligence around soil structure and drainage,” Christian told delegates.  

However, with good planning, there is scope to increase yield by a factor of three. Growers can set their soils up for success at the planning and preparation stage by modifying the root environment to alleviate stress, by improving aggregate stability and by focusing on structure and drainage.  

Desktop investigations and available literature can be used to understand regions, review rainfall and evaporation data. Tools include soil surveys, electromagnetic (EM) mapping, normalised difference vegetation index (NDVI), yield mapping, land levels and contour mapping, and soil pH mapping. 

Soils are often too wet due to poor drainage on-site or upslope drainage ingress, irrigation and soil incompatibility, groundwater, and problems with nutrition stemming from a lack of understanding.  

“Remember, drainage before irrigation,” Christian said. “Don’t get these the wrong way around. Define soil changes across landscapes and ensure irrigation is compatible with soil types to maximise yield, reduce stress and achieve sustainable water use.” 

Key message: Constraints must be ameliorated before planting or you have to live with them.  

• Take your time at the planning stage. 
• Optimal conditions are required at the land development stage (not just at time of planting).  
• Soil amelioration should be carried out to improve the soil environment for roots – aggregate stability, structure, drainage, rootzone depth.  
• Drainage is critical.  
• Collect physical and chemical data through soil surveys. Engage an expert who can offer high-quality interpretation.  
• Orchard management must ensure nothing stays too wet, soil structure is maintained, chemistry is monitored and adjusted, and groundcover is maintained at all times to prevent hardening and compaction.  

A native pollinator alternative? 

If the worst-case scenario occurs and the Varroa mite becomes endemic in Australia and decimates the European honey bee (Apis mellifera) population, there may be a native bee species up to the task of pollination – but only if the conditions are right.  

Dr Simon Tierney, Evolutionary Ecologist and Research Fellow at the University of Western Sydney, explained to delegates that many pollinator-dependent food industries in Australia are subject to a mismatch between native pollinators and introduced foreign plants. However, Simon’s research has identified a native stingless bee that could offer a pollination alternative for apple growers.  

Australia has about 10 per cent of the world’s bee diversity, yet scientists know very little about native bee foraging habits. This subject is becoming increasingly critical due to the threat of the Varroa mite to introduced European honey bees.  

Conducted over three years in twelve farms over two regions, Simon’s research sought to find out which bees are visiting apple flowers. The team video-recorded bees on flowers for over 19,000 minutes to create a profile of native bee behaviour.  

This data was leveraged to create a pollinator efficacy diagnostic tool, which found that native stingless bees are very effective pollinators and sometimes more effective than honey bees, but only on warm spring days on farms with close proximity to native forests.  

Key message: Australia has a unique evolutionary history and, as such, an ecological mismatch between native species and introduced foreign plants, for example, apples. A deeper understanding of native bees can aid the industry in maximising their efficacy, taking note of distance to habitat – for example, native bush – and temperature ranges in which they are most active. With the Varroa mite threat to the European honey bee these relationships may become more critical. 

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