The Mango Loa Project phase two: Improving Hawaii's mango industry by incorporating high density orchard management systems

2023 Final

Hawaii has never been able to develop a significant mango industry; in fact, here is a report on mangoes http://www.ctahr.hawaii.edu/oc/freepubs/pdf/B-12.pdf done in 1906 that outlines the steps we would need to take to establish a mango industry that is still mostly relevant today.  In my opinion, one of the primary reasons Hawaii has not been able to get a mango industry going is that most of the prime agricultural land was locked up by the sugarcane plantations and the only lands available were marginal lands that were too rocky for sugarcane with no irrigation.  Now that the sugar industry is gone, there are prime agriculture lands available and diversifying into mangoes seems like a realistic pivot.  

Another reason we have not developed our mango industry is that our population is small with 1.3 million people across seven islands and 1 million people on Oahu alone.  We are also rural and there are many mango trees being grown in people’s yards as well as along the sides of the roads that provide for our local communities.  What has changed today is that we have a thriving tourist industry that brings in over 10 million visitors throughout the state annually.  Kauai Island, where this project was conducted has 65,000 residents and around 30,000 tourists visiting each day.  The demand for mangoes and other tropical fruits is continuing to increase, and visitors to our islands want to eat locally grown tropical fruits during their stay.

So, we know that there is a high demand, by the amount of mangoes being imported and sold through box stores like Costco, and we know that we can grow a better product than any mango that is shipped to Hawaii.  However, our tropical fruit farmers have developed a less than good reputation for poor quality fruits as well as an inconsistent supply, and there is a lack of trust between the local farmers and the fruit distributors.  We are also on the low end for mango production.  The FAO says the world average for mango production is 3.5 tons/acre, and with great practices and varieties you can expect 5 or more tons/acre.  In Hawaii it may range from 0 to 5 tons/acre depending on the weather.  The goal of the Mango Loa Project was to introduce techniques that can help our farmers consistently produce upwards of five tons/acre of high quality mangoes.

 The Mango Loa Project began in 2017 with the goal of improving Hawaii’s mango industry by demonstrating an alternative orchard management system to increase production mango loa project phase 1.  Two different high density orchard management systems were used: the ultra high density plantation (UHDP) technique and the open Tatura trellis system.  These two systems have shown to increase the yield and quality of the mango harvest in other parts of the world, while reducing the demand on labor; all work is done from the ground, only requires hand tools (prune and saw), and hand harvest at eye level or with a short picker.  The trial began by planting 310 trees on a little over a half acre using the UHDP method.  That was followed up the next year by planting 300 trees on 5 open Tatura trellises on a little under a half acre.  This was phase 1 of the Mango Loa Project; planting 2 half acre fields of both high density orchard management systems and evaluating the installation and management of the orchard over 3 years leading up to harvest.  Phase 2 of the project was to continue on with the evaluation through years 4 and 5 of the orchard, with the hope of having a good harvest to observe.

Here are some quick takeaways from the project:

• Both the UHDP and the open Tatura trellis system were viewed as equal, in terms of management and demand of labor.  The open Tatura trellises were slightly more productive, however they require a $25,000/acre upfront installation cost that is hard to justify for a little better production.
• The best season was year 4 with a harvest of 8,000 lbs of Keitt mangoes, which represent around 1/3 of an acre.  With that, I believe it is reasonable to infer that a full acre of Keitt mangoes could have the potential to produce 12 tons per acre, significantly more than current standards and world averages.
• One change that I would make is adding more space in between the rows.  The spacing for the UHDP field was 10 feet between rows and the trellised field was 15 feet between rows.  Moving forward I would recommend 20 feet between rows for the UHDP field and 25 feet between the trellises.  The current spacing in the field can easily accommodate a riding mower, but is too dense for a tractor and the thickness of the canopy is making the field too shady and the air stagnant.  Widening out the rows will make operating in the field more comfortable for the tractor and for harvesting, and will allow for better airflow and sunlight exposure.
• There is a fatal flaw with the high density system and that is feral pigs.  Low hanging fruit is easy to harvest for the farmer, but is also easy for the pigs.  In the early years of the orchard, years 2 and 3, the pigs ate as much as 80% of the mangoes as well as broke all the low branches on the trees.  A perimeter fence is a necessity for this orchard management system, and if you cannot fence out feral pigs then high density orchard systems will not be as successful as the conventional mango orchard.
• Improving Hawaii’s mango industry is more complex than improved orchard management; it will also require a comprehensive approach to reducing losses along the entire mango supply chain.

If I had to guess, I would say that 50% of the mangoes we produce for the market make it to the market, and it may be much less than that.  Currently we have too many losses along every stage of the supply chain and reducing these losses through better practices will be the key to building a thriving sustainable mango industry.

Pre-harvest

The pre-harvest stage is anytime from planting to yearly management leading up to the harvest.  The orchard system is chosen at this time as well as the varieties picked for the market. What orchard management system will be used? Will it be conventional, high-density, or something in between.  The most important thing is that it is well organized and efficient.   The best varieties for commercial production are not always the best tasting mangoes, but must have a number of good characteristics that make them better than other mangoes such as: size, color, shelf life, even ripening, and taste. The tree itself has to be easily managed, a heavy bearer, a consistent yearly bearer, and disease resistant.   These two choices will have a very significant impact on the overall productivity of the orchard and whether or not it will be sustainable.  Pre-harvest is the stage where most losses occur and is also where most losses can be prevented through better management.

A good Integrated Pest Management (IPM) plan is necessary to reduce losses in the orchard caused by mammals, birds, insects and other pests, funguses, and all the other infestations and diseases that will affect production.  Losses caused by pigs, birds, fruit-flies, anthracnose, and powdery mildew can damage as high as 90% of the harvest every year if it goes unmanaged.  So, having an IPM plan in place will be critical in reducing losses leading up to harvest.  A good percentage off losses can be attributed to the lack of a proper spray management program beginning from the pre-flower stage to post-flower.       

Orchard management is also very important to production.  Pruning to increase the sunlight exposure and increased airflow is important for a healthy orchard.  Irrigating during fruit production will increase the size of the fruit and will minimize fruit drop and irrigating after pruning will speed up the new leaf flush.  Getting the correct nutrients into the plant at the correct growth stage will increase production.  These are the components that need to be fine tuned in the orchard and are necessary to maximize production.

High density orchard management systems allow the farmer to visually inspect the canopy of the tree for infestations, it is easier to see the growth stages’ from leaf flush to flowering, and you can see the flowers and the pollinator activities within the canopy.  Spraying can be managed with a backpack sprayer or a small utility vehicle.  Overall it is easier to inspect and manage trees that are 8 to 10 feet tall rather than 15 to 25 feet.  

Harvest

Minimizing damage during the picking is critical; scratching fruit with the picker, knocking down adjacent fruit, and picking immature fruit are some examples.  The high density orchard and the short trees allow the picker to fully observe the fruit to ensure that it is at the right maturity level for harvest and to carefully pick the fruit without damage.  Picking in the cool morning hours and keeping the fruit in the shade while picking will keep the internal fruit temperature down, which will slow down the ripening process.  It is also important to limit the amount of sap that touches the fruit skin, which will cause burns and blemishes making the fruit unmarketable.  

To prevent sap-burn, harvest the fruit with an inch or two of stem still attached to the fruit until you can get to a cool area, then break the stem and place the fruit stem end down so the sap can fall off without touching the skin. Another method to reduce sap-burn is to use a mango wash, which is a mixture of lye, detergent, and water.  Dunk the fruit into the mango wash or expose it to a spray of mango wash within a few seconds of picking to neutralize the sap.  There are a few mango wash products on the market from Australia, but they may not be available in Hawaii or the U.S.

Picking the fruit, de-sapping, and keeping the fruit as cool as possible before arriving at the packing house as quickly as possible are the goals during the harvest stage.

Post Harvest

The post-harvest stage is where a lot of losses occur because our local farmers don’t have access to cold storage and there is no way to cool the fruit to slow down the ripening, thereby extending the shelf life.  A lot of fruit is lost simply because it becomes overripe.  During this stage the mango is washed, sorted, packed, and cooled.  This is where you also see the losses from the pre-harvest and harvest stage: bug damaged, bird damaged, anthracnose, rub marks and scratches, and immature fruit are culled from the harvest and set aside.  

Mangoes should be picked green mature or at first color break and allowed to ripen on the counter to get the best quality and consistency, at room temperature this will give you a shelf life of 4 to 7 days.  Mangoes that are picked fully ripe on the tree are often overripe and the quality of the fruit may be inconsistent, at this point the shelf life is 2 to 4 days.  Mangoes should be cooled to 55°F to slow down the ripening process, giving the farmer and the retailer more time to sell the fruit.  Fully ripe mangoes can be stored for 7 to 10 days while maintaining quality, and green mature mangoes can be stored for even longer periods, however through studies we know that the acids in the fruit start to break down after 14 days and the quality diminishes the longer it is in storage.  Properly cooling mangoes will extend the shelf life of the fruit and will give the farmer, wholesaler, and retailer the most time possible to get the fruit into the hands of the consumer.  The reality is that prefabricated cool storage units are very expensive, need the space to house the unit, and access to electricity.  This makes it simply unaffordable for the small farmer.  However, over the last few years more examples of a do-it-yourself cold storage unit have been popping up, and this has been made possible by the CoolBot, which has been around since 2006. 

 The CoolBot is an external thermostat that can convert a window AC into a refrigerator and can lower the temperature into the low 40°F, cold enough to store tropical fruits at the optimal 55°F.  This device provides an affordable way for the small farmer to build a cold storage unit using a shipping container or spare room at a fraction of the cost of a prefabricated cold storage unit.  The unit can be built on-site and can be powered with solar panels if needed, making it affordable and convenient.    

Logistics 

Logistics is the process of getting the fruit from the packing house to the retailer in the most efficient way while maintaining the cold chain of command.  This is especially important when shipping fruits off island, where the fruit will have to be trucked to the harbor, put on a barge to Oahu, then back on another truck to the wholesaler or retailer, while maintaining the 55°F temperature.  Good communication and relationships are important to limiting losses caused by logistical problems.

Wholesaler, retailer, fruit processors, and consumers

Ideally, once your product is delivered to the wholesaler and retailers the chain of command has been passed on, they will continue the same practices to ensure a high quality product.  These are your business partners, and trust is paramount.  The fruit distributors need to trust that the farmer is providing a high quality product and the farmer has to trust them to do their best to sell the product.

The fruit processors are a major component of the mango supply chain.  Having an outlet for off-grade fruits that are marked or blemished, but still good for processing is necessary in order to reduce losses that occur in the pre-harvest/harvest stages.  Currently the outlets for off grade fruits are limited and often enough these fruits are left to rot.    There will always be off-grade fruits and the more mango we produce the more off-grade fruits we will have, to the point that as farmers we need to be able to use or sell our off-grade fruits for value added products, to capture the most revenue as possible.   Our ability to export mangoes outside of Hawaii is restrictive because of logistical reasons; unless you use airfreight (the most expensive) it would be really difficult to get mangoes from the farm to port, let alone the consumer, within 14 days, therefore we would lose our advantage over other mango producers and be just another commodity product with inconsistent quality. Even with the additional 10 million visitors to the islands each year, we would still be limited by fresh fruit sales.  In order to really expand our mango production, we will need mango processors that have the ability to process millions of pounds a year to make the numerous delicious products from mangoes. 

We can’t forget about the consumer.  Providing a consistent supply of locally grown mangoes picked to ripen into the deliciously sweet fruit we all love will keep consumers returning to buy more local grown mangoes over imported mangoes throughout the season.  There are no comparisons to the sweetness of our Hawaiian mangoes that practically sell themselves.

Research and Innovation

A thriving mango industry will require the ability to innovate and adapt in order to improve efficiency.  We need to know if there are new practices, varieties, or products that can help improve production.  Farming is very dynamic, always interacting with the environment and the climate.  Fortunately for the mango growers, there is a lot of research that has been conducted on mango production that we can apply in Hawaii.

Conclusion

It is hard to put a real number on the percentage of losses that occur along the supply chain, but we know that it is a lot.  On my farm I would say at least 50% of the harvest is lost through bird damage, bug damage, anthracnose, and overripe fruit.  My goal is to reduce these losses to 20% or less through better management and practices along each stage of the supply chain.  Increasing production by planting more trees and reducing losses through better management will be the changes needed to really build our mango industry.

At the Start of the Mango Loa Project in 2017, there was one small demonstration of the open Tatura trellis system on the island of Maui.  Today, there are ultra high density plantation mango orchards and open Tatura trellises on each of the major islands.  I have consulted with multiple farmers from each island and one thing they have in common is the plan to plant more mango trees.  Hawaii State has made it a priority to increase our food production and is opening up more prime agricultural lands to farmers. These farmers recognize mangoes as a viable crop; as we are seeing more plantings throughout the state, of grafted mango trees selected for their high quality good producing mangoes.  This is reflected by the most recent crop reports for tropical fruit production in Hawaii, conducted by the national agricultural statistics, in 2018 and 2021.  According to the report between the years 2018 to 2021, the total number of mango trees reported doubled from 15,100 to 33,500 trees and harvested trees nearly quadrupled from 6,600 trees to 24,600.  The total production increased by 60,000 pounds and the number of new trees planted has doubled.  I expect this upward trend for mango production in Hawaii will continue to grow as farmers plant more trees and mango consumption continues to increase around the world, especially in the U.S. and Europe, two of the largest demographics that visit our islands annually.  With that, there are many positive signs that Hawaii’s farmers are on the right track to having a sustainable mango future.

Open Tatura Trellis System Vs. The Ultra High Density Plantation Method

I have emphasized that the uhdp and the open Tatura trellis systems, as it is trialed in my project, is most suited for small farms with limited land, available labor, and will most likely be managed by hand.  In which case, this system is excellent and has been very productive.   However, the work is constant and intensive and can get overwhelming for a single person to manage.  I would guess that a single farmer, utilizing the ultra high density plantation system could manage three to five acres independently while a four-man crew could probably manage as much as 20 acres.  However, even at 20 acres, the farmer will need to consider time and labor saving practices like mechanization.  In large conventional orchards, tractor pruners are the standard.  In order to incorporate tractor management in the high density orchard, the rows will need to be widened to accommodate the machine and the trees can be allowed to grow slightly higher, 12 to 14 feet, to get the fruit higher off the ground. 

A significant factor to consider when determining if you want to plant a high density orchard is the ability to protect the fruit from ungulates and birds.  In Hawaii we have feral pigs, goats, deer, cows, chickens, and franklins that eat mangoes, damage trees, or both.  If the orchard cannot be fenced in, the uhdp orchard will not be successful.  In the first two years of the uhdp field, feral pigs broke over 100 trees, killing some.  In the third year in the ground and the first year with fruit, pigs and birds ate 90% of the crop, while breaking off lower branches on dozens of trees.  The field was fenced in after the third year and as a result we were able to have a decent harvest before pigs once again found its way in and damaged about 30% of the harvest.  This wouldn’t be nearly the issue in a conventional mango orchard where the majority of fruit is out of reach from the ground animals.  Low hanging fruit is not only a benefit to the farmers, but also for everything else. 

High density orchard systems need to be adapted specifically for Hawaii.  My experience with this technique so far leads me to believe that more than 300 trees per acre can be problematic. First it creates a really dense canopy that can reduce the airflow in the orchard, making the trees susceptible to infestations of insects like aphids, scales, mealybugs, and mites; all of which damage the fruit.  Stagnated airflow can also lead to powdery mildew and anthracnose damage as well.  The thick canopy also restricts sunlight from achieving optimal penetration, which will also diminish the quality of the fruit.   Pruning one time after harvest is not enough to create sufficient airflow and sunlight distribution and five months post-pruning,  when the flowering season begins the canopy is just as dense as it was before the pruning (this is true on the trellis as well). Multiple pruning sessions in a year is time consuming, runs the risk of pruning off flowering wood, or if you prune after fruit set, it is possible to sunburn the fruit.

The most significant difference between these two systems is the additional cost and labor to install the trellises; the management practices have been similar as well as the production.  The cost per acre for the trellises is around $20,000 which would be a real impediment for a small farmer and while the production may start earlier and be slightly better than the uhdp system, it would be hard to justify that upfront cost.  There are a few concerns with managing the trellised field; one is the ability to manage the vigor in the orchard.  The Tatura trellis system was developed for temperate-zone fruits, like apples, pears, and peaches; and temperate zone fruits have the benefit of a dormant period during the winter where there is no growth, couple that with heavy production during the growing season and the vigor of the trees become more manageable.  Also, many of these fruit trees have dwarf varieties which ultimately make growing fruits on the trellises successful.  At this point, it is difficult to maintain a two-dimensional canopy, through a single pruning while multiple pruning sessions may eventually effect the flowering cycle.  Also multiple leaf flushes before flowering often puts the fruit on the ground and more effort is needed to keep the fruit in its designated space.  Lastly, the longevity of the wood posts is a concern.  I have seen wood post fail within two years, most likely due to inadequate treatment of the wood, making it susceptible to termite damage, which was the cause of the failure in this case.  While a benefit of the trellis is that it can protect the tree limbs from damage during a storm, if a trellis does break, it may be an insurmountable challenge to fix.  Of course, a solution to this problem may be to use metal or concrete posts, but that would just raise the already high cost of installation. 

With all that said, the most important recommendation would be to widen out the spacing in both the uhdp field and the open Tatura trellis field.  This is the direction that I’ve already begun to move toward and the most recent field was planted at a density of 250 trees an acre, as opposed to the 450 tree density that was planted for this project.  This is a spacing of 10 feet by 20 ft, compared to the 8 feet by 10 ft spacing of the uhdp field.  This will leave plenty of space for the tractor and other machinery to operate.  This would also open up the orchard to more airflow and sunlight and improving the quality of the fruit.   As for the open Tatura trellis field, the recommendation would be to widen the space between the trellises.  The trellises for the project were spaced 15 feet apart, which does not leave enough space for a midsize tractor to go through.  Spacing the trellises 20-25 feet apart will ensure there is enough room to work in.  it would be really difficult to manage with a tractor pruner, but I think it is possible.  At least the outsides of the trellises; the insides of the trellises might not have enough space to safely maneuver.  A recommendation may be to use an espalier style trellis as an alternative to the open Tatura trellis.  I would also recommendation widening out the spacing between trees on the trellis from 8 feet to 10-12 feet; this would allow for more air and light into the orchard and would reduce the demand on the farmer to produce grafted trees. The last recommendation would be to start the bottom trellis wire at 36 inches instead of 24 inches; this would be to get the fruit higher off the ground.