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Ethephon and its use on macadamia nuts

By Jim Patch and Kevin Quinlan, MPC


The use of Ethephon (eg Ethrel®) after crop maturity has many potential benefits, including cost savings to growers or the potential for growers to have more time to complete other tasks before the start of the next season.

The cost benefits to the grower go far beyond a reduction in harvest time. The quality of the product harvested and paid for by a processor may also be of higher value, with longer shelf-life than nuts which are retained on the tree or lie on the ground for an extended period of time.
Nuts remaining on the tree for an extended period can suffer from lipid oxidation (rancidity) and a reduction in kernel oil content and kernel value.

By using Ethephon pest and disease management may also be improved in some later falling varieties like A16 and Daddow due to the break produced between mature nut fall and flowering and early nut development of the next season’s crop. The use of ethephon may ‘buy quality time’, allowing you to complete worthwhile orchard operations before the start of the next season. Some benefits observed by the use of Ethephon include:

  • Increase in harvest efficiency
  • Reduction in harvest costs
  • Improvement in kernel quality
  • Improved NIS and kernel value
  • Efficiency in harvest timing to suit other orchard operations (e.g. canopy management & surface water management)
  • Break between nut drop and flowering of the next crop reducing the potential for insect and/or disease carryover
  • Reduction in rodent damage for the ensuing crop

How Ethephon works

The synthetically manufactured Ethephon in products like Ethrel® breaks down in plants to release ethylene, a naturally occurring product that is produced in many plants during their ripening process. In macadamias, the ripening action is centred on the abscission zone in the base of the ‘pedicel’ (the stem that holds the nut to the rachis/raceme), and to a lesser extent the ‘leaf petiole’ (base of the leaf stork where it attaches to the stem/limb of the tree).

The abscission zone in the pedicel is restricted in shape and size and the cells are smaller in size than conventional cells. When Ethylene is applied to these cells, they enlarge, forcing the restricted abscission zone apart, abscising the nut.

Ethephon’s break down products are ethylene, phosphate and chloride which are all metabolised by the plant.
There are many factors that affect the success of Ethephon in causing nut abscission including the variety, ambient temperature and the stress levels of the tree.

Past Research

There has been a reasonable amount of research carried out by the Australian Macadamia Industry and Southern African Macadamia Growers’ Association into the use of Ethephon in macadamias. Examples include:

  • MC 00029 Final Report – ‘Investigation of nut abscission and tree shaking’. McConchie, C.A. & Salter, B. Horticulture Australia Ltd. 2005;
  • MC 97005 Final Report – ‘Control of nut abscission in macadamia’. Turnbull, C, Trueman, S. et al, Horticulture Australia Ltd. 2002;
  • ‘Ethephon as an aid to macadamia harvesting in South Africa’. Penter, M. ARC-Institute for Tropical and Subtropical Crops. Nelspruit South Africa. 2004.

Is coverage important?

Yes. It is thought Ethephon is not translocated by the tree far from where it is applied and therefore it is important to apply Ethephon to achieve good coverage of the nuts. High volume spraying to the point of run off is best. When applying Ethephon, ensure the inside of the tree and tops are covered to achieve best results.

Do all varieties drop well when Ethephon is applied?

The simple answer is no! It appears cultivars that naturally have a high nut drop rate have the best response to Ethephon and require the lowest dose rate (e.g. Var.344, 741,246 and 849). Varieties that have a poor drop rate (e.g. A16) do not respond as well to Ethephon and require the highest dose rate to achieve a satisfactory result.

When is the best time to apply Ethephon?

The time of application is a balance between leaving the application long enough to allow macadamia nuts to reach full maturity and applying while temperatures are still warm enough to get a good response.

If you are planning to apply Ethephon, you should utilise MPC’s maturity testing service to determine when nuts have reached maturity. This ensures you get the best financial return from the product.

It is thought temperature, both soil and ambient, affect the efficacy of Ethephon. From observation and research it appears the product is more rapidly metabolised with warmer soil temperatures which may provide a more satisfactory result. A higher rate of Ethephon® may have to be added to a mixture to achieve a satisfactory result as soil temperatures decline. The lowest soil temperature that provides a satisfactory result is not presently available.

It is has been found the best results from Ethephon application occurs when natural nut drop has commenced. To get the best result you need to monitor nut drop to determine when to apply the product .
In general, the best results with Ethephon have been observed when it is applied in late March/early April to mid May after nuts have reached maturity. Research has indicated most varieties are mature by end March/early April in the Lismore area of NSW. Nut maturity in Queensland may be slightly earlier and the Mid Coast region of NSW a little later, so application timing needs to allow for this.

Will stick tight nuts fall after spraying with Ethephon?

No. Ethephon is only effective in living plant tissue. Stick tight nuts are not affected because tissue in the husk is dead. Growers have observed even green husks that have split in the tree will not drop with Ethephon application.

How long does it take for the nuts to drop?

When nuts are mature, it may take from 14 to 28 days after application for nut drop to be completed. In hard to drop varieties like A16, some crop may still drop after this timeframe, but the majority of crop will be down within this period of time. In varieties that shed well naturally (e.g. 344/741), some crop may start to be shed in five to seven days after application and complete nut drop reached by day 14. Because Ethephon will condense nut drop, be prepared to harvest with high nut volumes on the ground.

Does Ethephon increase leaf drop?

Ethepon causes leaves to drop more quickly than usual and in general the higher the rate of application the higher the leaf drop potential. It appears some varieties may be more prone to heavy leaf drop than others e.g. variety 842. Leaves that drop are usually 12 – 18 months old and may have very little photosynthetic input into the tree at that time. Growers have commented leaf drop from A16 trees is a good thing as it reduces leaf density, allowing more light into the tree.

Research reported a heavier leaf drop in the first year Ethephon was used and reduced leaf drop in subsequent years. It is thought leaves did not fall to the same extent in the second year because there were not as many old leaves left on the tree. Growers have observed leaves that are shed by a tree from an Ethephon® application usually don’t equal the quantity of leaves naturally shed anually, especially in variety 246.

Some growers who experienced what they believed was excessive leaf drop, greatly reduced the Ethephon rate in the following year (e.g. reduced the active by 50%) and experienced far less leaf drop while maintaining a similar quantity of nut drop but over a longer period.

As leaf drop can be affected by application rate, growers intending to use Ethephon should conduct small scale trials to get a better understanding of the quantity required for each variety and their location to get the best balance between acceptable nut and leaf drop.

How long does it take for old leaves to drop?

Leaf drop peak usually occurs about a week to a fortnight after nut drop peak . For example, if nuts drop in 14 days, leaves will probably drop from about day 21 to 28. Varieties 842 and A16 may have extensive leaf drop. Due to increased leaf drop, growers need to be ready to harvest quickly when they observe heavy nut drop from Ethephon application.

What dose rate best suits my region and varieties?

The use of Ethephon was initially registered and started in macadamias for varieties H2 and Own Choice which have stick tights and late nut drop patterns. The Australian Macadamia Society (AMS) has obtained the current permit for Ethephon use on all macadamia varieties. As part of the permit issued by the Australian Pesticides and Veterinary Medicines Authority (APVMA), growers were required to complete a questionnaire about their experiences with Ethephon on different varieties and submit this information to the AMS. The following information is a summary prepared by MPC from that data covering the years 2004-2007, and MPC acknowledges the assistance provided by the AMS in providing the data for this analysis.

NOTE: The following rates are for products containing 480g/L of active ingredient. If you intend to use a different strength adjust your rate accordingly (see “How do I calculate the dose rate for products that do not contain 480g/L of active”).

The TABLE(S) below and over are a guide only and as nut and leaf drop are affected by application rates, growers intending to use Ethephon should conduct small scale trials first to get the best balance between acceptable nut and leaf drop.






* NOTE: Products containing 720g/L of Ethephon are not recommending in low volume spray applications.

How do I calculate dose rate for products not containing 480g/L of active?

There are different active rates of Ethephon in products like Ethrel® and so you need to calculate the correct application rate. Generally suggested rates are quoted for 480g/L of active products. If the recommended rate is 125ml/100L of Ethrel® 480 but the product on hand is Ethrel® 720, you need to change the active rate in the mixture. The calculation to do this is:

480/New Active strength x Rate
e.g. Rate = (480/720) x 125
= 83.3 mls/100L
Therefore the rate of Ethrel 720 to use is 83.3mls per 100 litres of water.

Can I use other products to increase the effectiveness of Ethephon?

Yes. It is recommended that a suitable non-ionic wetter (e.g. Nufarm Chemwet® 1000) be added at a rate of 100ml /100 litres of water. The wetter should be added prior to Ethephon. Read the surfactant/wetter product label for suitability and directions first.

Research was conducted in South Africa by Penter et al in 2002;2003 into various spray adjuvants to find if the efficacy of Ethephon can be enhanced by their addition to the spray mix. These adjuvants included wetters, phosphates, urea and combinations of these products. Drop rates were not improved over the use of a suitable rate of non-ionic wetter by the addition of the extra adjuvants.

Tank mixing considerations

It’s important Ethephon is thoroughly mixed with water and non-ionic wetter in the spray tank during tank filling and prior to spraying. Adverse results have been achieved if this is not done.

Management considerations

Using Ethephon may condense your harvest into one major round. It is important you have capacity to harvest, dehusk, store and deliver to the processor in a short period . A rain event or the inability to cope with increased nut drop has to be taken into consideration when planning the application of Ethephon.

An effective strategy used by growers to reduce the risk of crop loss or not being able to cope with a large volume of nuts in a short time, has been to split their applications over a number of weeks, only applying the product to the number of trees they can harvest and dehusk at weekly intervals.

The plan has to be flexible with allowances made for rainfall events and the ability to harvest/dehusk in a timely manner.

Other reasons to use Ethephon

Ethephon may be a good tool for use in areas where you wish to carry out a special project before you would normally finish harvesting. e.g. tree removal for surface water or light management.

These areas may be sprayed to ensure harvest is completed early, the project work completed and trees have a chance to adjust to the new conditions before the next crop set .

The use of Ethephon to allow major canopy management projects like tree removal to be completed and the remaining trees given time to adjust to the increased light penetration has the potential to reduce yield impacts compared to doing this work later in the year.

In the case of orchard floor drainage works, it allows soil that is moved time to settle and grass to establish before the summer storm season and the following seasons’ harvest preparations.

Can Ethephon be used on young trees?

Yes. Ethephon may be used on young trees to remove the need to hand harvest the trees and reduce the cost of harvesting. An application of Ethephon can allow you to use mechanical harvesting as only 1-2 harvest rounds may be required, reducing the cost of harvesting considerably. Care should be taken to ensure the accurate calibration of an airblast sprayer or hand gun that may be used to avoid over-dosing of the young tree.

Can I use Ethephon on Stressed trees?

Trees under stress may be adversely affected by an application of Ethephon®. The cause of the tree stress may include: water stress (too much or too little); excessively hot temperature; mechanical damage (tree breakage); insect or disease damage. Such trees should not be sprayed with Ethephon until they have recovered.

Is the effect of repeated applications in one season accumulative?

Yes. Two applications of 60ml/100 litres of water in one season may have the same effect as one application of 120ml /100 litres of water. It is advisable to conduct a trial on a few trees to determine the correct rate, as you essentially only get one shot per season.

OH&S/Operator safety implications

Ethephon is rated ‘Poisonous’ and there are a range of precautions needed when using this product. Read the label carefully prior to use.

Will using Ethephon affect next years crop?

Research was conducted on the use of Ethephon on macadamias for three consecutive years by McConchie and Salter in Bundaberg. It was noted that neither cropping nor tree health were effected during this time. Research conducted by Trueman in Australia found a slight improvement in production following the third year of application of Ethephon. Research conducted in South Africa by Penter et al has come to a similar conclusion. Penter found there was a slight increase in nut production in the ensuing season after the use of Ethephon which is believed to be the result of improved light infiltration following the shedding of older leaves due to the application of Ethephon.

Grower Experiences

Rick Paine has been using Ethephon® to condense his nut drop and reduce stick tights in A16s for the past eight seasons. He is keen to produce the highest quality kernel from his orchard and knows that nuts which remain on the trees for extended periods loose kernel quality. He has not detected any ill effects on either the health of his trees or in cropping from use of Ethephon.

Rick emphasises it is critical to apply Ethephon at the correct time, at an accurate rate and provide full coverage to achieve success with the product.Rick ensures the sprayer is calibrated to cover the entire tree including the area inside the canopy and to the top of the foliage.

Rick’s airblast sprayer sprays the bottom section of his trees. Thorough coverage is ensured at the top of his tree using SARDI fans mounted on a frame on the front of the tractor, which positions the fans towards the tree top. The SARDI sprayer is not used when spraying the smaller 849 trees in the orchard.
Maturity tests are conducted by the MPC nut in shell laboratory to ensure nuts are mature and are used to determine the correct timing for Ethephon application. Rick has found if he applies Ethephon spray too early the nuts do not drop.

Rick did not have a good result with Ethephon in 2011 as he believes the nuts matured later than usual and so they had to apply it later than they would normally do. He also believes the soil temperature may have been too low at this time to get a good response.

Rick applies Ethephon to 1000 trees at two week intervals as this is the number of trees that he can manage with his harvesting and dehusking set up with a large volume of nut on the ground. His orchard is relatively flat, so he is able to harvest shortly after rain. He grows a range of varieties including 344,741, A4, A16 and 849. His priority for Ethephon use is on A16’s because of the stick tight nature of the crop and 849’s because they drop over a long period and he wants to condense the nut drop.

Rick sprays the A16’s soon after the MPC lab results indicate that they are mature. In warmer seasons he has found he can achieve favourable results with the 849’s until mid May. Other varieties are less important as they drop naturally in a more condensed pattern. He does apply Ethephon to these varieties at a reduced rate (see Table 1 below) to condense the harvest if there is a project that is to be conducted in these blocks , such as limb removal. Rick said it is his intention to continue using Ethephon as he has found it to be a very beneficial tool in condensing his harvest and thus providing savings in on-farm costs and maintaining kernel quality.

Rick Paine


John has been using Ethephon since 2004. His aim is to condense harvest time, ensure A16 nuts drop with reduced stick tight nuts retained and to ensure ‘best payments’ for his crop by having high quality kernel to sell. Ethephon has been successful at ‘Zulumac’ and is now a part of regular management practice. Since using Ethephon to condense the harvest time to finish by the end of June, the trees have been given a break before flowering/nut production commences for the next season. Insect, disease and rodent damage has also been minimised as a result of this break.

John Pretorius

John now has the time to conduct his canopy /light management operations in July-August, prior to the nut expansion period (September –December) so relieving the competition that exists between vegetative growth and nut growth for essential seen in figure 1.


John said he can not detect any effect on the health or cropping ability of his trees that may be attributed to extended Ethephon use.

Ethephon is applied to completely cover all leaves and nuts to ‘run off’ by an air blast sprayer. John has found that coverage is critical to getting good results.

The timing of application is determined by the understanding gained about crop maturity through maturity tests conducted by the MPC NIS laboratory.

When the crop is mature and nut drop has commenced, John applies Ethephon to A16s and then to Hawaiian varieties to the number of trees that he knows can be managed by the harvester and dehusking in a few days when the nuts have dropped.

John tries to complete Ethephon applications before the soil temperature drops below 18°C as he believes he gets a better result at or above this temperature.

The benefits resulting from Ethephon® use at Zulumac are many, and include:

  • Reduced harvest length and time
  • No more harvest rounds per year than when harvesting monthly (See Figure 2)
  • Less pressure on dehusking shed
  • Less nuts per harvest round – more efficient pick up with a pin wheel harvester
  • Improved ability to plan deliveries to the processor
  • Last years nuts are not carried over and harvested /wasted this year
  • Canopy management conducted in winter
  • Break period for trees after harvest before new crop set
  • Break period to reduce insect, disease and rodent damage in ensuing crop
  • Improved quality
  • Above average payments for crop.


Current Rates used

And what is John’s overall take on Ethephon?
Because Ethephon has been proven to work so well as part of his present orchard management he feels “very confident to continue using the product in the future”.

  • Ethrel® 480. 200ml/100L water +10ml Agral 600 (surfactant) @ 6.0L mixture/tree
  • Ethrel® 720. 130ml/100L water + 10ml Agral 600 @ 6.0 L mixture/tree

Hawaiian varieties

  • Ethrel® 480. 120ml/100L water + 10ml Agral 600 @ 5.6L/tree mixture
  • Ethrel® 720. 80ml/100L water + 10ml Agral 600 @ 5.6L/tree mixture.