Growing low chill stonefruit
Common questions

Alan George & Bob Nissen, Department of Primary Industries and Fisheries.

This information has been extracted from the Agrilink Low Chill Stonefruit Information Kit and the Agrilink Low Chill Stonefruit Information Kit Annual Update 1999, which provide information on all aspects of growing and marketing low chill stonefruit in Queensland.

• Introduction
• Varieties and rootstocks
• Pruning and thinning
• Preparation for planting
• Pests
• Problems
• Postharvest treatment
• Quality assurance
• Planning
• Spraying
• Further information

Introduction

This section contains the most commonly asked questions about growing low chill stonefruit. The answers are as brief as possible. Where this is difficult and more detail is required, we refer you to other sections of the information kit.

Varieties and rootstocks

What variety should I plant?

This is a difficult question to answer simply as it involves several different factors. The first is your farm location and the amount of chilling it receives. This determines the range of suitable varieties available to you. The choice of these varieties then depends on the type of market you are going to target-early, mid or late season, or a combination to spread the risk. The final choice also depends on whether you specialise in peaches, nectarines or plums or a combination. We provide more detail on this decision in the information kit.

Which is the best rootstock for low chill stonefruit?

The most commonly used and recommended rootstock is coastal peach. Different nurseries use various selections of coastal peach. This is a vigorous rootstock and is generally compatible with most varieties of low chill stonefruit. Its main problem is susceptibility to nematode damage. Where soils are very sandy and a nematode soil test indicates nematodes are present, use Okinawa or Flordaguard. These have better nematode resistance but should not be used in alkaline soils. As none of the rootstocks has good resistance to root and trunk rot, it is essential that well drained soils are used for all low chill stonefruit plantings.

If I want to do my own grafting, can I use budwood from my neighbour's trees?

It is preferable not to use budwood from other orchards because of the risk of bringing in virus diseases. These diseases can affect yield, fruit quality, fruit maturity time and tree vigour. Instead, use the special virus-tested budwood available from specialist budwood suppliers. Varieites under Plant Breeders Rights cannot be propergated by unauthorised persons.

Pruning and thinning

How do I prune low chill stonefruit trees?

Pruning low chill stonefruit trees is complex. We provide full detail in other sections of the kit. As well as studying these sections, attend any pruning field days or short courses to gain practical field experience. Basically you are aiming for an open tree with good light penetration into the centre to stimulate lots of new fruiting wood. This can only be achieved with a combination of winter and summer pruning.

When should I thin fruit?

The best time to thin is at flowering before the fruit has formed. This is also the time when the job is easier and quicker. Thinning at flowering also leaves you with the option of thinning later if required to fine-tune your final level of fruit set. Where there is a risk of late frosts, or where there appears to have been insufficient chilling, delay thinning and thin fruitlets instead.

How can I get larger fruit?

It is important to remember that fruit of early maturing varieties, because of their shorter period of development, are naturally smaller. There are limits to what can be achieved here. The best way of improving fruit size is to thin the crop so there are fewer fruit left on the tree. However, take care as over-thinning may cause split stone and skin cracking in some varieties such as Flordaprince and SunWright. Paclobutrazol, a growth retardant, may also help to achieve larger fruit size but needs to be used with great care.

Preparation for planting

At what spacing should I plant my trees?

Spacing depends on your climate and the pruning or training system that you decide to use. For warmer areas such as coastal Queensland and northern New South Wales, we suggest 4 m between rows and 3 m between trees (palmette), and 5.5 to 6m between rows and 4.5 to 5 m between trees (open vase). For cooler areas such as Kingaroy, we suggest 4 m between rows and 2.5m between trees (palmette), and 5 to 5.5m between rows and 4.5 to 5m between trees (open vase). Any spacings less than these, particularly on fertile soils and/or under warmer growing conditions, will require some method of growth control such as the use of growth retardant.

Where can I buy trees?

Most specialist tree fruit nurseries stock low chill stonefruit trees. Before purchase, check whether the nursery is using virus-tested budwood and seed to propagate their trees.

Pests

How do I control fruit fly?

There are a number of strategies to control fruit fly.

• Most importantly, use fruit fly traps to monitor fly numbers. This helps to determine when fruit fly spraying should start. Set up traps early in the season well before fruit start to colour. When fly numbers over three to four days reach 20 per trap, start spraying.
• Use a combination of bait sprays and cover sprays. Bait sprays are recommended at weekly intervals up until four weeks before harvest. Then apply weekly cover sprays of fenthion until harvest. Observe withholding periods. Details of registered chemicals are contained in the Problem Solver Handy Guide in the kit.
• Regularly monitor fruit for gumming and fly sting marks so that the spray program can be refined where required.

What is the Carpophilus or 'dried fruit' beetle?

Carpophilus is a genus of small beetle that normally pollinates custard apple flowers. The beetles are becoming significant pests in some low chill stonefruit areas. They enter ripening fruit through cracks and wounds, feeding on the flesh and at the same time spreading diseases such as brown rot among fruit and trees. Chemical for control of this pest are registered for use on stonefruit.

How do I control birds?

Experience has shown that the only long-term successful method of bird control is total exclusion bird netting. This involves completely enclosing whole blocks of trees with nets supported on poles and wires above the trees. Most scaring mechanisms generally only work for a short time as the birds quickly get used to them. Recently developed electronic scaring devices are more effective but do not offer the same long term advantages as netting.

How do I control flying foxes?

The best control for flying foxes is the total exclusion netting used for bird control. Experience has shown that all other mechanisms are of limited value, particularly when feeding pressure is high.

Problems

Why are my leaves going yellow and falling off?

Stonefruit leaves will yellow and fall naturally as the trees go dormant. However, when leaves yellow and fall off early, say before the end of April, it means that there is another problem. This is generally water stress, insufficient nitrogen, heavy spider mite infestation or high levels of rust or shot hole disease. Although less common, severe leaf fall may also result from spraying with a mixture of mancozeb and fenthion.

• For water stress, ensure that trees receive enough water from rain or irrigation until March. This is particularly important in drier areas.
• With nitrogen, trees need enough nitrogen to keep them going until natural dormancy around May-June. If there's been heavy rain in summer and autumn, more nitrogen may be needed.
• For spider mite, a spray may be necessary if there is insufficient build-up of natural predators.
• For diseases such as rust and shot hole, maintain a regular spray program. Also, do not use mixtures of mancozeb and fenthion. The fungicide, chlorothalonil, is the preferred alternative to mancozeb for disease control.

Why are my trees flowering early?

Trees flower early because the leaves have fallen early. Anything that causes the leaves to drop early will cause early flowering. When leaves fall and temperatures are still mild enough, trees are induced into an early dormancy and start to flower. Fruit set from this flowering will develop over winter and is generally not marketable. There are three main causes of early leaf fall: poor control of rust and/or bacterial spot disease, insufficient nitrogen, or insufficient water. The problem is exacerbated by a lack of summer pruning.

What causes gum to ooze out of my trees?

The cause of gum oozing out of trees can be difficult to diagnose as any sort of damage to stonefruit trees produces gumming around the damaged area.

• Gumming confined to low down on the trunk is generally caused by Phytophthora disease. This is particularly common in younger trees up to two years old. The problem is often exacerbated by damage from the herbicide glyphosate.
• If the gumming is higher up in the tree, the probable cause is San José scale, white peach scale or hail damage.
• Gumming on the trunk and branches of older trees is generally caused by peach tree fungal gummosis disease. This disease produces copious amounts of gum, particularly after rain in January.
• A milder symptom of gummosis is swollen lenticels (breathing pores) oozing gum.

What has caused my tree to die?

The most common cause of tree death in low chill stonefruit is root rot disease caused by Phytophthora. This means that the site probably has insufficient drainage. The other common cause of tree death is a heavy infestation of either San José, scale or white peach scale or both.

What is this mouldy stuff on my fruit?

There are two likely causes of mould on fruit. The most likely is brown rot disease where the mould tends to be grey-brown, powdery and not elevated much above the skin. This disease can be a major problem in crowded orchards and spraying is recommended. Details of registered chemicals are contained in the Problem Solver Handy Guide in the kit. The other possible cause is Rhizopus rot where the mould is grey-black, fluffy and elevated above the skin. It is generally only a problem in the field in damaged fruit and is more common during transit and storage.

Why are parts of my tree dying?

There are several possible explanations. Heavy infestations of either San José, scale or white peach scale or both may kill branches. Phytophthora infection of the trunk and girdling of branches by fungal gummosis may produce similar branch death. Brown rot disease also causes a blighting of branches. The other possible cause is a tree reaction to too many full strength oil sprays. More than two or three oil sprays in a season are likely to produce this effect.

Why do my trees flower so profusely?

Low chill stonefruit varieties, most of which originate from Florida, have been deliberately bred for prolific flowering. This characteristic has been incorporated to ensure that at least some flowers survive the late frosts regularly experienced in north and central Florida.

Postharvest treatment

Do I need to treat my fruit?

Yes. Low chill stonefruit should be treated with a postharvest fungicide to stop destructive postharvest diseases such as brown rot and Rhizopus rot. If you are marketing your fruit in states other than Queensland and New South Wales, the fruit may also need to be treated with an approved insecticide for Queensland fruit fly.

Quality assurance

Do I need quality assurance (QA) and at what level?

Buyers are now demanding some level of quality assurance (QA) in fresh food marketing and all growers will need some form of QA. Different levels of QA are required depending on where you intend to market your fruit. Several QA systems are being promoted within the industry but the choice depends on what best suits your needs and your purchaser's requirements.

Planning

Is my farm suitable for low chill stonefruit?

The main requirement for low chill stonefruit is well-drained soil without heavy clay or rock within 1 m of the surface. As stonefruit can be grown in frosty sites, there are few climatic limitations. Warmer areas need to receive sufficient winter chilling. In colder areas, there is a risk of damage to blossom from late frosts. An adequate supply of good quality irrigation water is essential.

What yield can I expect from my trees?

The average yield for a mature low chill stonefruit orchard generally ranges from 15 to 20 t/ha for an early variety such as Flordaprince to around 25 to 30 t/ha for a later maturing variety such as Flordagold. However, yields of 25 t/ha for Flordaprince and 35 t/ha for Flordagold are achievable in some better managed orchards.

When will trees start bearing fruit?

Trees will generally start to bear fruit at about 18 months to two years from planting. Trees are at full bearing stage by about the fourth year.

How many trees should I plant?

A viable living for a couple is about 3 to 4 ha of low chill stonefruit trees. A farm of this size will need to employ casual labour to complete pruning, fruit thinning, harvesting and packing.

How many different varieties should I plant?

On a small orchard, it is best to plant only one or two varieties. On larger orchards, the choice depends on whether you are going to target early, mid or late season fruit. Remember that as each variety has different management needs, it is best not to plant too many different varieties.

How long will my trees last before I need to replant?

Under good growing conditions, low chill stonefruit trees should have a productive life of about 15 years. However, the continual advent of new improved varieties and the market force to upgrade to them means that this figure is largely academic. Planning and development of the orchard should therefore budget on a tree life of about 8 to 12 years.

How can I prevent hail damage to fruit?

The only practical prevention is to make the exclusion netting used for bird and flying fox control double as a hail protection system. This means that the net type selected has to have hail protection properties and the netting system designed for this extra function.

How profitable is growing low chill stonefruit?

Profitability depends on the:

• quality of your product and the market reputation you develop
• efficiency of your orchard management and how much additional labour you need to employ.

An average mature orchard under good management could be expected to return a gross margin (income less production costs) of about $20 000 to $25 000 per hectare per year.

Is low chill stonefruit difficult to grow?

All stonefruit have a large management requirement. However, low chill stonefruit are the most demanding of all stonefruit varieties. For example, low chill stonefruit must be pruned three times a year, and flowers and fruit must be thinned by hand. This is extremely time-consuming. There is also an intense period of harvesting, and a regular spray schedule. You should only contemplate growing low chill stonefruit if you believe you can master all of these requirements.

Can I grow low chill stonefruit organically?

For a number of reasons, it is difficult to grow low chill stonefruit organically. The large number of potentially serious pest and disease problems makes effective control by non-chemical methods very difficult. In addition, there may be statutory laws requiring the control of some pests and diseases. The intensive cropping pattern of low chill stonefruit also makes it difficult to achieve profitable yields and fruit quality from organic fertilisers.

Spraying

Do I need to spray a lot?

Yes. Several pests and diseases attack stonefruit and a regular spray program must be applied. This involves spraying about weekly from September to March for either pests or diseases or both.

Are these chemicals safe to use?

Although all chemicals are potentially hazardous, chemicals registered on low chill stonefruit can be safely applied providing that you act responsibly, use good spray equipment and take adequate precautions. This means reading the label, observing all safety recommendations, regularly calibrating your spray equipment and only spraying when weather conditions are suitable. All registered chemicals have approved residue limits, which will generally not be exceeded provided label recommendations are followed.

How do I get spray accreditation?

Spray accreditation can be obtained by attending a course provided by an accredited trainer. In Queensland the certificate is known as ChemCert Australia Farm Chemical User Accreditation. In other states other names are used eg. SMARTtrain in NSW.

Do I need training in the safe use of chemicals?

In some states you cannot buy chemicals unless you have a current spray accreditation or have suitable authorisation. An authorised person is one whose business is selling or supplying agricultural chemical products, or who is a state licensed spray contractor or has ChemCert Australia Farm Chemical User Accreditation.

Currently, by law in Queensland, you only need training in safe use of chemicals if you are a contractor spraying on other people's land or you want to buy restricted chemicals. However, most customers now see it as highly desirable for their growers to be able to demonstrate safe, responsible use of chemicals. One of the best ways to demonstrate this is to obtain ChemCert accreditation. Remember spray accreditations must be renewed every five years.

How should I store my chemicals?

Chemicals need to be stored in accordance with the AS-2507 standard. This does not mean you will have to spend a fortune on elaborate storage facilities. You do, however, need to be aware of several environmental and food safety factors whenever you deal with chemicals. Further information on correct use of chemicals is covered in the chemical user course. ChemCert accredited trainers also understand these requirements. Employees of farm chemical resellers with ChemCert accreditations are also a useful source of information.

How do I calibrate my spray equipment?

Equipment needs to be calibrated to work efficiently and the results of this calibration should be documented. You will learn the correct calibration method at the spray accreditation course. Nozzles should be changed regularly to ensure correct spray droplet formation and delivery of volume.

Do I need to keep a diary of spraying records?

Yes. Records of chemical applications are now one of the most important pieces of documentation you will need to be able to prove what you have done with chemicals. All buyers of your produce for supply to the retail sector now expect you to keep spray records. You should record: what crop was sprayed and the area; what was applied; how much per 100L and how much spray volume (L/area); what pest or disease was targeted; what application method was used and by whom; and when the application took place.

Will spraying my trees affect my neighbours?

Provided you exercise care with the application of all chemicals, it is unlikely that chemical sprays will drift to neighbouring properties. These precautions include selecting equipment that minimises drift, avoiding spraying under windy conditions and establishing strategically placed windbreaks on the edge of the orchard. We also recommended that you discuss with your neighbours the nature of your spraying program and the safety of the chemicals you are using.

Further information

The complete Agrilink Low Chill Stonefruit Information Kit provides information on all aspects of growing and marketing low chill stonefruit in Queensland and northern New South Wales.

The kit includes the following sections:

• Before you start
  A checklist of things you need to know before you start growing the crop.
• Common questions
  The twenty or so most commonly asked questions about growing the crop.
• Growing the crop
  Our guide for establishing, producing and marketing the crop.
• Key issues
  Detailed information on the key decisions affecting the crop.
• Problem solver
  A picture series of the common problems and how to solve them.
• Contacts and references
  A list of industry organisations, product suppliers, and further reading.
• Index
  An A to Z index to help you find information quickly.
• Your information
  A place for you to store your special information.

The Agrilink Low Chill Stonefruit Information Kit  is currently out of print, however a photocopy may be obtained from the Information Centre at the DPI&F's Redlands Research Station, phone (07) 3824 9555.

For commercial enquiries on low chill stonefruit, contact the DPI&F on telephone 13 25 23 between 8 a.m. and 6 p.m. weekdays; non-Queensland residents phone (07) 3404 6999. E-mail: callweb@dpi.qld.gov.au

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Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries, Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.

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Last updated 11 October 2007