Growing Citrus
common questions
Noel Vock, Dan Smith, Garry Fullelove, Department of Primary Industries and Fisheries.
This information has been extracted from the Agrilink Citrus Information Kit, which provide information on all aspects of growing and marketing citrus in Queensland.
Introduction
This section contains the most commonly asked questions about growing citrus. The answers are as brief as possible. Where this is difficult and more detail is required, we refer you to other sections of the Agrilink Citrus Information Kit.
Problems
My leaves are turning yellow. What's the problem?
If all the leaves on the tree are turning yellow, the problem is most likely root rot or collar rot caused by the Phytophthora fungus. Winter yellows is another but less common alternative. If the yellowing leaves are accompanied by some dieback of the twigs on Hickson mandarin, the problem will most likely be crotch rot. If only some leaves are going yellow, the problem is most likely to be a deficiency of zinc, magnesium, manganese or iron.
My fruit are falling off. What's causing this?
Fruit fall is most common in Navel orange because this variety can't tolerate water stress very well. As a result, very hot conditions in November, December and January will regularly cause fruit drop. Too much water can also cause Navels to drop fruit. Fruit drop in Ellendale and Murcott mandarins generally occurs because trees are either too heavily laden or fruit are over mature. A drop of young fruit in November/December is natural as the tree sheds excess fruit.
Why are my Imperial mandarin fruit very dry?
This is somewhat natural for Imperial mandarins. Young trees on Troyer rootstock may have a fair number of dry fruit under hot, dry conditions. If older trees for some reason set a very light crop, a large number of the fruit will be dry and misshapen. Excess nitrogen fertiliser makes the problem worse. It is important in Imperials to carefully monitor nitrogen by leaf and soil analysis. Also manage thinning very carefully to avoid alternate heavy and light crops.
What causes irregular dark marks on the skin?
There are a lot of causes of marks on the skin of your fruit. These include wind rub, spray damage, oleocellosis, sunburn and stylar end rot. Symptoms of each of these conditions are shown in Section 5, Problem Solver, of the kit.
I've got borers in my trees. How do I treat them?
There are two types of borers, each with different treatment methods. Identify which type of borer you have. If it is the more superficial trunk and branch damage from the fig and speckled longicorn beetles, scrape away any insect frass and sawdust and spray affected areas with an appropriate chemical.
While there is no chemical specifically registered for borer control, the methidathion spray used for white louse scale control also controls borers. Apply the spray in sufficient volume of water to thoroughly wet the affected area.
The other type of borer is branch borer, which kills individual branches and leaves distinct holes in the wood. It is worse in wetter coastal areas in orchards adjacent to rainforest. With this type of borer, it is important to identify the problem early by regularly checking trees for signs of slight branch wilting. When observed, remove affected branches promptly. Trees in a vigorous healthy condition are also less susceptible to attack.
Why aren't my Navel trees setting much fruit?
It is part of the nature of Navel trees, which are very sensitive to water stress. If this occurs in September/October, few fruit will be set. Similarly, if water stress occurs during November, December and January, young fruit that has set will drop off.
Why are limes getting this brown end on the fruit?
This is a problem called blossom-end rot or stylar end rot. It is mainly caused by the fruit being over-mature on the tree. As limes are meant to be harvested green, harvest the fruit before the colour begins to lighten off towards yellow. Avoid any water stress near the green harvest time.
Why are the tips of outside branches of my trees dying back?
The most likely cause is a condition known as blight, for which there is no treatment. Another cause on Navel oranges and Imperial mandarins is a disease called anthracnose. This is a stress-related problem and can only be minimised by using the copper sprays recommended for control of black spot and melanose. Root rot and collar rot can also cause twig dieback.
Planting
What varieties and rootstocks should I plant?
This is a difficult question to answer as variety and rootstock choice depends on many factors. The choice of variety depends largely on which part of the state you are in, and which markets you are targeting. The choice of rootstock will depend on your soil type and the variety you select.
For more details on varieties and rootstocks refer to the Agrilink Citrus Information Kit. We also recommend that serious intending commercial growers discuss variety and rootstock selection with an experienced citrus consultant.
What mandarin variety should I plant in this area?
The most suitable standard varieties are Imperial, Hickson, Ellendale and Murcott. Promising new varieties are Afourer and Daisy. Sunburst and Fremont are being widely planted but there is insufficient data to form a reasonable opinion.
All of these varieties are generally suitable for drier coastal and inland areas. For the wetter coastal areas, it is suggested that Murcott and Sunburst should not be planted.
What lemon varieties should I plant?
On the Queensland coast, Meyer is the best variety, though it is not a true lemon. In the drier inland areas of Queensland, use Eureka, Lisbon and Villa Franca.
How close can I plant citrus?
The standard spacing for citrus is 7.3 m between the rows and 5.5 m between the trees in the rows. For oranges, lemons, grapefruit and Ellendale mandarins, tree spacing within the rows can be reduced to 3.6 m but alternate trees will have to be removed later. For mandarins other than the Ellendale variety, tree spacing within the rows can be further reduced to about 2 m, again with alternate tree removal later. However, this very close spacing requires a high level of management.
A close-planting alternative for high density planting is the double row system. This has double rows planted 2.4 m apart with 7.3 m between the centres of each double row (centre of double row to centre of double row). Trees are planted within the rows at a spacing of 2.4 m.
Tree management
Should I mulch my citrus trees?
Yes, but keep the mulch about a hand span from the trunk. If you are mulching trees on heavy soils, adjust the amount and frequency of your irrigation so that trees are not over watered.
How do people grow lemons and limes out of season?
Lemons and limes can be grown out of season by following the Verdelli system developed in Italy. This system means withholding water from the tree until you want it to flower. At that time, you water and fertilise with urea. This system is not practical in the wetter coastal areas of Queensland because the rainfall is unpredictable and is likely to come when you don't want it. In these areas, the best system is to use the Meyer variety, which can be harvested in November, December and January.
How much irrigation water should I apply to citrus?
This depends on the age of the trees, the time of year, the variety and the amount of rain that you get. As a general rule, it may vary from about 1000 L per tree per month in winter to about 5000 L per tree per month in summer. The most reliable way to work out how much water to apply is to use a soil moisture monitoring device. The three most common ones are tensiometers, neutron probes and Enviroscans.
Is there any control for Phytophthora root rot disease?
Yes. The best way to minimise the problem is to spray the foliage with phosphorous acid. Details of registered products are contained in the Problem Solver Handy Guide. Two sprays a year are recommended-the first just before flowering and the second in autumn, around late March or early April. Use the higher label rates of the chemical if you have prolonged wet weather, susceptible rootstocks, marginal soils or over watering problems. Apply the chemical in at least 8000 L/ha of water. Trunk injection of the chemical is impractical and soil application is not recommended.
What sort of sprayer should I buy for citrus?
For young trees up to 2 m high, a high volume air blast machine without tower is satisfactory. As the trees grow larger and older, an oscillating hydraulic boom sprayer is preferred. Air blast machines with towers can be used but must be operated effectively in well pruned orchards.
How do I know when my fruit is ready to harvest?
Fruit has to reach a specified maturity standard before it can be harvested. This is determined by taking a sample of your fruit and having it tested. It cannot be determined by looking at the fruit.
Can you help me interpret my leaf and soil analysis results?
The results from leaf and soil analysis show levels of nutrients in your leaf tissue or soil. These can then be compared with critical levels established from extensive research. If your levels are above the critical levels, you don't normally need to apply much fertiliser. If your levels are below the critical levels, you need to apply fertiliser to get your levels back to the critical levels. Interpretation of the figures is a complex process and should be done by trained agronomists or consultants.
Money
What is an economical area of citrus to grow?
If growing citrus is to be your sole source of income, then you need a minimum of 18 to 20 ha of trees. Space for roads, houses, sheds and fences is extra. A farm size of about 50 ha is recommended to allow the planting of replacement blocks every ten years or so and the introduction of new varieties. If you intend to become an individual exporter, then a minimum of 50 ha is generally required.
What does it cost to grow citrus?
By the time you have bought a suitable farm of 20 ha or more, purchased the necessary machinery, developed the water supply, planted the trees, looked after them and built an equipped packing shed, you will have a capital outlay approaching $1 million by about the fifth year. Capital costs can be significantly reduced by buying second-hand equipment, using specialist machinery contractors and joining a packing and marketing cooperative. After the orchard has been set up, it generally costs up to $20 000 per hectare per year to grow and market the crop.
What yield can I expect from my trees?
Yield varies widely depending on the size of the tree, the variety and the planting density of the orchard. For an orchard of normal density (7.3 m between rows and 3.5 to 5 m between trees), average yields range from about 9 kg (half a citrus carton) per tree in the third year to about 150 to 180 kg (8 to 10 citrus cartons) for a mature tree in the tenth year. Using these figures, a mature orchard should be expected to produce 2500 to 3000 citrus cartons per hectare per year.
Higher per hectare yields up to about the sixth year can be obtained with high density planting. This makes much better use of available land but requires a higher level of management.
Degreening
What is the system and chemical used for colouring fruit?
The system for colouring fruit is called degreening, the chemical used is ethylene and the method used is called trickle degreening.
How much ethylene do I use for degreening citrus?
The concentration of ethylene required is between 3 and 10 parts per million of the fresh air intake. Air intake is between 1 and 2% of the room volume per minute.
What are the brown marks on the skin of fruit after they come out of the degreening room?
This is a condition known as 'degreening burn' and is believed to be associated with the anthracnose fungus. Several factors are known to predispose the fruit to damage. These include picking fruit when immature, abnormal degreening conditions and moisture and nutrient imbalances close to harvest. Growth of the anthracnose fungus in the skin is triggered by ethylene during the degreening process. Some of the marking develops during degreening but it often occurs during and after packing.
Starting an orchard
I'm thinking of growing limes. What do you think of the idea?
Limes have good potential but you first need to do some market research. Carefully study the price and throughput data for the major markets. Then research your ability to produce limes in your area during the period of higher prices. The only reliable way to do this is by following the Verdelli system. This means withholding water from the trees until you want them to flower. At that time you water and fertilise with urea. This system is not practical in many areas of Queensland because the rainfall is unpredictable and is likely to come when you don't want it. Proceed only if you are confident of your ability to get this system to work.
Where do I buy good planting material?
Buy your citrus trees from a specialist citrus or fruit tree nursery. These nurseries generally have access to virus-free budwood and seed for propagation.
Where do I get citrus seed and budwood?
Seed may be bought from the Queensland Citrus Improvement Committee (QCIC), PO Box 48, Gayndah QLD 4625 (Phone: (07) 4161 1116). Budwood should always be obtained from the Australian Citrus Propagation Society Inc, 15 Bowen Crescent, West Gosford, NSW 2250 (Phone: (02) 4325 0247).
Spraying
How much of chemical xyz do I need to mix in a tank of water?
Details on mixing rates of chemicals are contained on the product label. These are normally quoted as so much per 100 L of water. If your tank holds 500 L, all you need to do is multiply the label rate by five to determine how much chemical you put in your tank. Mixing rates of the most commonly used chemicals in citrus are shown in the Problem Solver Handy Guide.
Should I be going into IPM in citrus?
There is no simple answer to this question. Integrated Pest Management (IPM) has some very significant advantages and we would like to see all growers move into IPM as soon as possible. However, it does have some risks and is not foolproof. It requires a very high level of management to achieve the advantages on offer. We suggest you read the available material on IPM and then discuss your transition to IPM with a citrus pest consultant.
How do I control fruit fly?
The recommended control is the use of fruit fly bait sprays, which are mixtures of an insecticide, an attractant (yeast autolysate) and water. The mixture is sprayed low down on the foliage of trees as a coarse spray of about 50 mL per tree.
Registered insecticides for the bait sprays are chlorpyrifos, maldison (Hy-Mal) and trichlorfon (Dipterex). Trichlorfon bait spray is not recommended at times of high fruit fly pressure.
For multiple cropping varieties such as Meyer and Lisbon lemons, bait spraying is recommended all year round. For early varieties (e.g. Navel, Imperial), bait spraying should start in January; for mid season varieties (e.g. Ellendale, Hickson), in March; and for late season varieties (e.g. Valencia, Murcott), in May.
Can I mix my chemicals together?
There is no short answer as several different chemicals are used in citrus and their mixing ability varies widely. Look first on the label for mixing advice. If there is insufficient information there, check with your chemical retailer or integrated pest management consultant.
How do I get spray accreditation?
Spray accreditations can be obtained by attending a course provided by an accredited Chemsafe Training Queensland trainer.
Do I need training in the safe use of chemicals?
In some Australian states you cannot buy chemicals unless you have a current spray 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 wholesalers and retailers 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 a Chemsafe 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 AS2507-1998 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 safety, environmental and food safety factors whenever you deal with chemicals.
Further information on correct use of chemicals is covered in the chemical user course. Agsafe or Chemsafe accredited trainers also understand these requirements and employees of farm chemical resellers with Agsafe accreditations are also useful sources of information. The address for Chemsafe Training Queensland is: PO Box 3128 SOUTH BRISBANE QLD 4101S. Ph: (07) 3844 7261; Fax: (07) 3844 7307; e-mail: chemsafe@powerup.com.au
Do I need to keep a diary of spraying records?
Yes, you do. Records of chemical application 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 the merchants and agents supplying the retail sector now expect you to keep spray records showing at least what was applied, how much, by whom, and when the application took place.
Marketing
Can I send citrus fruit to other states?
Yes, citrus may be sent to all Australian states but requires treatment or special certification for all states except New South Wales and the Northern Territory. In New South Wales, fruit may not be consigned into the quarantine areas of the Murrumbidgee Irrigation Area (MIA), Sunraysia and mid-Murray without a special permit. Following the successful eradication of papaya fruit fly in Queensland, the special restrictions applying to the movement of citrus out of the Papaya Fruit Fly Quarantine Zone no longer apply.
Home garden/hobbyist questions
My leaves are curling and going brown. What's the problem?
This is damage from the leafminer insect. You only need to control it in trees under four years old and then only on significant growth flushes between January and March. Spray each of the new flushes when the new leaves are just emerging (10 to 20 mm long). Use an appropriate chemical selected from the Problem Solver Handy Guide. Follow label directions.
My citrus tree has died. What would have caused this?
There are several reasons why trees die. If the tree died without starting to grow, then the most likely cause is root rot disease. Other reasons for trees dying are forgetting to take the bag off the tree before it was planted, putting fertiliser into the hole at planting, leaving the hose running on the tree for too long, and mulching up to the trunk. A heavy red scale infestation may also kill young trees and will kill branches on more mature trees.
I've planted a tree but it hasn't really grown. What's wrong?
There are several possibilities. The most common is poor planting technique where there has been insufficient contact between the roots of the root ball and the surrounding soil. This means that the roots have not been able to grow out into the surrounding soil. This problem is often worse in older container-grown trees where roots have become pot-bound. Another common reason for trees not growing is root rot from heavy clay soils staying too wet after rain or watering.
I've got borers in my citrus tree. How do I treat them?
As the borers are generally inside the wood of the tree, they are often hard to get at and chemical treatments may be ineffective. If the borers are in a branch or branches, cut off the affected branches at a point well below the visible area of borer attack and burn the pruned branches. If the borers are in the trunk, there is little that can be done apart from poking a thin wire into the borer holes in the hope of killing the insect. Keep the area around the tree clear of weeds. Also check your neighbour's trees to see if you can identify the source of the borers. Keep your tree in a healthy vigorous condition as this makes it less susceptible to borer attack.
What is this black stuff on my leaves and fruit?
This is called sooty mould. It looks worse than it really is and doesn't hurt the leaves or fruit. Sooty mould is a fungus growing on sugary deposits made by scale insects, mealybugs and some other insects. Scale insects are the most common culprit. Remove the scale and the black mould will disappear.
What's causing the yellow patterns in my leaves?
It is most likely a deficiency of zinc, manganese or magnesium. Zinc and manganese deficiency cause yellow blotches between the leaf veins. Magnesium deficiency causes yellowing of the leaf margins while the central part of the base of the leaf remains green.
What are these lumps on the branches of my tree?
The lumps are caused by the citrus gall wasp. For home garden trees, there is no practical chemical control. Prune out the twigs and branches containing the worst galls and burn the prunings. In commercial orchards, we recommend spraying susceptible grapefruit and mandarins with an appropriate chemical from the Problem Solver Handy Guide in early December, to coincide with hatching of the gall wasp eggs.
Should I put manure or fertiliser in the hole when I plant my tree?
No. Start fertilising only when the tree has started to grow healthy new leaves.
Further information
The complete Agrilink Citrus Information Kit - RRP $95 + $9.50 GST (Total $104.50), produced by the Agrilink Information Unit of the DPI&F, provides information on all aspects of growing and marketing citrus in Queensland. It is available from the Agrilink office (phone 1800 677 640) or the DPI&FShop On-line.
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 to store your special information.
For enquiries on citrus, contact:
- DPI&F Business Information Centre on 13 25 23 - local call 8 am to 6 pm Monday to Friday (non-Queensland residents phone 07 3404 6999). E-mail: callweb@dpi.qld.gov.au
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.
Last updated 04 February
