Growing potatoes
Common questions
Stephen Harper, Eric Coleman, Craig Henderson & Jerry Lovatt, Department of Primary Industries and Fisheries, Queensland.
On this page:
Introduction
This section contains updated information on the most commonly asked questions about growing potatoes. The answers are as brief as possible, more detail is contained in the 'Agrilink Potato Information Kit' which provides information on all aspects of growing and marketing potatoes in Queensland. Whilst this information kit is now out of print, copies may be available in some libraries and DPI&F information centres.
In the field
What are good rotations for potatoes?
Sweet corn, forage sorghum, grain sorghum, maize, sugar cane and lucerne are all good, commonly used rotations. However each of these rotations may have other external factors that need to be considered, such as the type of herbicide used on them, or specific disease issues. For example, forage sorghum may increase the amount of rhizoctonia fungi in the soil, and areas that have grown sugar cane may have residual herbicide problems.
What caused this leaf roll?
There are several causes of leaf roll and it can be difficult to decide whether it is a physical, nutritional (mineral) or a virus leaf roll. Physical leaf roll can result from water and wind stress. Nutritional leaf roll can be caused by a variety of deficiencies or in some cases a toxicity of certain minerals. For a positive identification do a full nutrient analysis. Plant samples must be tested in a laboratory to confirm leaf roll virus.
If it's virus leaf roll, did it come in the seed?
If certified seed potatoes were used, it is highly unlikely that the virus came in the seed. However if symptoms appeared shortly after emergence it may have come in the seed. If virus leaf roll occurs in the later stages of the crop, aphids probably carried the virus in and then transmitted it from plant to plant. Very late infection may not produce visible symptoms unless tubers from this crop are used for seed.
Why are these plants wilting?
Plants may be wilting from moisture stress or because of a soil-borne disease (e.g. bacterial wilt) reducing the movement of water and sap through the plant system. Wilting could also be caused by root damage from insects such as whitefringed weevil.
Why has this potato crop died off so suddenly?
The crop most likely died off because of leaf disease, soil-borne disease or early seedpiece breakdown. Inspect the plant residue for signs of leaf and soil diseases. The other probable cause is waterlogging.
Do you think this crop is a bit short of water?
The crop may lack water, but check the plant below ground level as well as observing the top. Check the moisture around the roots regularly during growth and know how much water different sized crops use.
Tensiometers are a good guide to water requirements, irrigate when the shallow tensiometer (20 cm) reaches 30 to 40 centibars. A range of electronic and automatic logging devices are also available.
What sort of yield do you think this crop will produce?
There is no hard or fast answer. Yield will depend on the variety, age of the crop and several other factors.
How many more weeks do you think this crop will last?
The crop should be checked regularly from 12 to 14 weeks after planting to determine optimum harvest time. The time to harvest depends on the variety, the level of disease and the crop management practices adopted as well as seasonal conditions. Markets also have an influence, as premiums or penalties may result from different grade sizes. Time of planting also affects the length of the growing season.
Pests and diseases
Is this purple top wilt?
Symptoms of purple top wilt are purpling of the top leaves, and small tubers growing in the leaf axils (aerial tubers).
Why have I got an aphid problem even though the crop is regularly sprayed?
Either your spray application methods need to improve to give better coverage, the chemical you applied is ineffective or aphids are continually migrating into the crop. A granular insecticide is registered for application at planting to control aphids.
Which is the best pesticide to use?
All of the registered pesticides are effective if used properly for the appropriate pest. If pesticides are applied as directed on the label, it is unusual for pests or weeds to persist. If pesticides are not working, they are probably either not being used correctly or alternatively the crop or pest is at a stage where control is becoming difficult. For example, spray coverage on leaves may be poor in a crop that has a full canopy, or an insect pest may be too mature to achieve good control.
How do I control potato tuber moth?
Tuber moth is not a serious pest of the growing plant but can be damaging at harvest. It invades the tuber through cracks in the ground, so growers should reduce tuber moth populations before harvest. Rolling the potato hills and irrigating to reduce the number of cracks in the soil will lessen the exposure of tubers to potato tuber moth. There are several pesticides registered if control is necessary. The Orgilus wasp is a natural parasite and may help to reduce the numbers of tuber moth. If the wasp is released into the crop use soft insecticides such as a Bt to avoid killing them.
Large numbers of tuber moth at harvest time are difficult to control. Do not store potatoes in the ground or delay harvesting if there are large numbers of tuber moth as sprays are ineffective at this stage.
Potato tuber moth can sometimes be found in seed potatoes from other Australian states. Although the infestation may be within the level specified for certified seed, growers may prefer to ask their seed grower to treat the seed before shipment. If the seed was not treated and there is evidence of tuber moth on arrival, tip the seed out as soon as it arrives and treat it with a seed dust. Follow label directions.
What causes scabs on potatoes?
Two types of true scab can affect potatoes: powdery scab and common scab. Powdery scab is the most common in cool weather crops, whereas common scab is usually found in warmer conditions. Scab-like lesions can form on potatoes damaged by insects early in development. The tubers' wound healing process can sometimes result in the formation of a scab.
What causes stem end rot?
The main causes of stem end rot are the fungi Fusarium and Phomopsis. Other soil-borne diseases occasionally result in rotting of the stem end. An accumulation of reducing sugars can also cause a breakdown of the stem end of the tuber. An accumulation of reducing sugars can also cause a breakdown of the stem end of the tuber.
What causes basal stem rot?
Basal stem rot is a physical breakdown of the stem that can be caused when mature plants (about 12 weeks old) that have been grown under soft conditions are exposed to hot or windy stressful conditions. These soft plants become top heavy and collapse. The exposed stem base can be sunburnt, then become infected causing it to rot.
How do I control crickets?
Mole crickets are a major problem in potatoes because they burrow through the tubers. Control is by baiting, using the insecticide chlorpyrifos mixed with bran, or a soil application of another registered pesticide. Soil fumigation before planting may also control crickets.
How do I control whitefringed weevil?
Numbers of damaging larvae can be significantly reduced over time through crop rotation, which breaks the insect's life cycle. There is a registered pesticide that can be applied and incorporated into the soil. Soil fumigation prior to planting may also control whitefringed weevil.
Seed
Should I dip my seed?
Dipping of seed is not recommended unless common scab, powdery scab or Rhizoctonia black scurf is detected. This is unlikely if certified seed potato is used.
Should I plant straight after cutting or should I let the seed heal a bit?
It is best to let the cuts heal (suberise) properly before planting.
Could I keep seed from this crop for planting in a few months?
In north Queensland, most potatoes are grown in the winter months. Few people keep seed from a crop grown from certified seed (called 'once off' certified seed) because the risk of virus infection and/or poor vigour is too high. To minimise this risk the seed must be kept under cool room conditions for several months, this should not be considered in north Queensland.
In the Lockyer Valley, most growers save the small potatoes from their winter crop grown from certified seed for planting in February. This seed is stored in a cool room and taken out three to four weeks before the crop is to be planted. Like north Queensland, there are some problems with seed-borne virus diseases, particularly from early planted crops that are susceptible to aphid attack. This has traditionally been the only source of seed for crops planted in February. Seed for this crop is planted as whole round sets to avoid seedpiece breakdown under the hot humid conditions at this time of year.
I've got poor emergence due to seedpiece breakdown. Can you tell me what has happened?
There are four possible reasons for poor emergence:
- The seed was planted immediately after cutting and soil conditions were too dry or too wet to heal the cut, allowing secondary rots to attack the seed.
- Too much irrigation or unexpected heavy rain has waterlogged the soil. The seed has then decayed through lack of oxygen.
- Fertiliser has damaged the seed because it was placed close to or on top of the fertiliser band. This damages the cut seed surface and can allow secondary breakdown of the seedpiece.
- The seed was physiologically too young.
Where do I buy potato seed?
Buy certified seed if possible and only use 'once off' seed that has been produced under your control for autumn planting. Do not buy seed from other producers, particularly from other districts, unless it is certified.
How much disease is allowable in certified seed?
The certified seed scheme in each state specifies the amount of disease that is allowable. There is a NIL tolerance for some important diseases, but some tolerance of other pests and diseases is allowed in some schemes.
Why does one seed source appear to yield better than another?
This does not happen often and is generally inconsistent. It often depends on the season in which the seed was grown and the age of the seed when planted. This is not a genetic problem; in most cases it is due to the age of the seed. Ensure all eyes are showing signs of sprouting (breaking dormancy). Regardless of the source, seed is derived from the same basic genetic material.
Is there any advantage in using round seed?
Yes, there are several advantages and only one disadvantage. The advantages are:
- you should almost eliminate seedpiece breakdown when compared with cut seed;
- the seed is more evenly shot because of its even size and age;
- mechanically cut seed sometimes has no eyes in the seedpiece and is more likely to breakdown in the soil after planting;
- the cost of cutting seed is eliminated.
The disadvantage is that it costs more to get round, size-graded seed. In the future, certified seed growers will be producing more round seed (small tubers).
Varieties
What variety should I plant?
For commercial production, the choice of variety depends on the market you are targeting. For the fresh potato market, Sebago is the main variety for the unwashed (brushed) trade, while in Queensland, Desiree (pink/red), Nadine (white), Red La Soda (red) and Snow Gem (white), are the main varieties for the washed trade. Atlantic is the main variety for the crisping potato market.
A range of 'gourmet' varieties including Kiffler, King Edward, Purple Congo, Nicola, Bintje, Rosval and Pink Fir Apple are also available.
What has happened to Sebago?
Some industry people believe that Sebago is not performing as well as it has in the past. This variety may have deteriorated genetically due to continual selection from a limited amount of genetic stock. Sebago is also one of the most susceptible varieties to blackleg, leaf roll virus and seedpiece breakdown. As well as searching for alternative varieties, plant breeders are trying to improve the strain of Sebago as it is the preferred variety by merchants for the general table trade. The decline in vigour of Sebago may also relate to a decline in soil productivity under more intense cropping.
Planting
What is the ideal soil temperature for planting potatoes?
The ideal soil temperature for potato growth is between 15° and 20°C. Avoid planting at temperatures below 10°C and above 26.5°C.
How far apart should I plant the seed?
Seed spacing depends on market demands. If you are growing potatoes for crisps, or red potatoes for pre-packing, you may need to plant closer than if you are growing a Sebago potato for the fresh market. Other considerations are the size of the seedpiece, variety and age of the seed.
Fertilising, irrigation and weed control
Can I use poultry and other manures on my crop?
There is now some concern about the suitability of manures for vegetable production due to the possibility of microbiological contamination of the produce. This has mainly affected crops that are eaten fresh. Crops like potatoes that are cooked before eating are less of a concern. As with all quality assurance and food safety issues it is important to have a good understanding of what your customer requires and expects.
Should I give my potatoes some more nitrogen?
If the crop is in the last month before harvest, no. A potato crop does not benefit from additional nitrogen at this stage. In the early stages of the crop, some nitrogen fertiliser is generally applied shortly after emergence. The only other situation where additional nitrogen fertiliser may be required is to generate new growth after significant damage from frost, hail or wind.
Should I put some foliar fertiliser on my potatoes?
Apply foliar fertiliser if a leaf analysis at flowering indicates a need. Foliar fertilisers may provide some benefit where crops have been severely damaged by frost, hail or wind or where specific trace elements are deficient.
Should I try some of the organic fertiliser blends?
Potatoes like a lot of organic matter, but the only way to achieve high inputs is either through a green manure crop or as large quantities of an organic amendment. Do not apply large amounts of manure if common scab is known to occur.
Organic matter improves soil structure, which in turn improves drainage and the moisture-holding capacity of the soil. It also increases nutrient availability and can reduce the incidence of soil-borne diseases.
Is my irrigation water too salty for potatoes?
Get your irrigation water tested. If the conductivity level (salt content) of the water exceeds 1.8 deciSiemens per centimetre (dS/cm), expect lower yields.
What can I do to get rid of late weeds?
Although weeds may cause some problems at harvest, they are unlikely to reduce yields. In the Lockyer Valley, late weeds are not normally a problem. However, try and manage your weeds through the cropping cycle so they do not set seed and cause problems for your next crop.
Some weeds are desirable in both spring and autumn crops. Weeds use excess soil moisture and reduce harvest delays if storm rainfall occurs in spring. Weed cover also shades soil reducing the incidence of potato heat necrosis (brown fleck). In the autumn crop, which is often left in the ground for a few weeks after full maturity, the weeds use excess soil moisture in the cool months and reduce harvest delays. However, it is still important to try to minimise weed seed set.
An alternative to letting some weeds grow to soak up excess moisture is to oversow the crop with oats in winter, or French millet. Oversowing should be done about five weeks before your expected harvest date. This also reduces the risk of weeds setting seeds.
Using chemicals
What is the best spray equipment to use?
There is no one best type; buy spray equipment that suits your situation and budget. In some districts, large areas may be sprayed by aircraft. Boom sprays are the most commonly used ground equipment. Select equipment based on its ability to give good coverage of the target area.
How do I calibrate my spray equipment?
To work efficiently, equipment needs to be calibrated. Ensure nozzles and filters are cleaned and maintained regularly and operating within the designers specifications. Document the results of this calibration as part of your quality management system, and keep it with your spray diary.
What is an MRL?
MRL stands for Maximum Residue Limit, which is the maximum level of a chemical permitted to be present in a food. It is expressed as milligrams of active ingredient per kilogram (mg/kg) of the food. Produce at the markets is randomly tested for chemical residue. Farmers have been prosecuted when chemical residues were above the MRL, or residues of non-registered chemicals were found.
What is a withholding period (WHP)?
The withholding period is the number of days that must pass between the last chemical application and harvest for human consumption, grazing by livestock and cutting for stock feed. For postharvest treatments it is the number of days from the postharvest treatment to consumption. The WHP will be on the pesticide label. Some chemicals do not have WHPs for livestock, if these chemicals are used, the crop must not be fed to livestock. The WHP for livestock consumption may be greater than that for human consumption. Residues should be below the MRL if the chemicals are used at the registered rate and frequency, and the withholding period is observed.
How do I get chemical application accreditation?
You must attend a ChemCert Farm Chemical User Training course. Course participants complete an open book assessment at the end of the course and successful candidates are then issued with a statement of accreditation by ChemCert. This accreditation is valid for five years.
Do I need training in the safe use of chemicals?
In some states you cannot buy certain pesticides unless you have a current ChemCert accreditation and in Australia, endosulfan can now only be supplied to or used by an accredited person. ChemCert accreditation will assist the documentation of a quality assurance (QA) program. It is highly desirable for growers to be able to demonstrate safe, responsible use of chemicals. One of the best ways to demonstrate this is to obtain ChemCert accreditation. These accreditations must be renewed every five years so participants are kept up to date with changes and developments.
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 but you need to be aware of several safety, environmental and food safety factors when dealing with chemicals.
Do I need to keep a diary of spraying records?
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. Most 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. This information is an essential part of a QA system.
Environmental management
What is an EMS?
An Environmental Management System (EMS) is a systematic approach to managing the impacts that a business has on the environment. An EMS does not dictate levels of environmental performance, however it should enable a business to comply with legislative requirements concerning the environment. It should also build on existing activities such as industry best management practices, industry codes of practice and quality assurance schemes.
What type of EMS do I need?
We do not know when or what type of EMS will be required in the horticulture industry in the next few years. It will depend in part on the markets you are aiming to supply. As a minimum, you should become familiar with the Growcom Farmcare Code of Practice for fruit and vegetables. It was developed by Growcom to assist growers meet their general environmental duty of care under the Environmental Protection Act 1994.
The most widely recognised auditable international EMS standard is ISO 14001. This process standard requires a business to have an implemented, documented environmental policy in place which is available to the public. It also requires the business to have a documented environmental management system in place that is capable of being audited by an accredited third party. ISO 14001 does not prescribe specific levels of environmental performance but it does require a business to be able to identify and have access to all relevant environmental legislation.
In Europe, a protocol based on good agricultural practice called EurepGAP has been operating since the late 1990s. A significant number of Australian horticultural businesses are working towards EurepGAP in order to meet compliance deadlines stipulated by UK/ European retailers and importers.
What is Enviroveg?
Enviroveg is a relatively new program from the Australian Vegetable and Potato Growers Federation (AUSVEG). Enviroveg is committed to encouraging vegetable growers throughout Australia to adopt and implement good environmental practices. It includes a self-assessment tool to help growers compare their current farming practices with the environmental best practice activities listed in the Enviroveg guidelines.
Farm safety
What are my workplace health and safety obligations?
Australian agriculture has one of the highest rates of workplace accidents. Your obligation as an employer and farm manager are based on three principles:
. a concern for people and their well-being including yourself and your family;
. sound business management;
. compliance with current workplace health and safety legislation.
The best way to meet your obligations is to take part in the Managing Farm Safety program developed by Farmsafe Australia. The Managing Farm Safety program is aimed at developing skills in risk management of farm safety - an approach that is consistent with the way other farm business risks are managed. The training course and resource package are based on real data about the major risks on Australian farms, including specific agricultural industries, and takes into account the requirements of current occupational health and safety legislation.
Harvesting and marketing
When is the crop mature?
A common method of determining maturity is when the skins are firmly set on the tubers-that is when the skin is not easily rubbed off with the thumb.
What are the grade standards for potatoes?
There are no longer legal grade standards in force. Some buyers set their own standards so check the requirements of your proposed market. If none exist, use the legal grade standards that previously existed as a guide for packing.
How do I label the bags?
There are specific requirements for labelling and marking potatoes for sale. They are either a separate label attached to the bag/package or a marking on the bag/package itself. The label needs to show the growers' name or company name and address. A key food safety requirement is traceability. All potatoes need to be identified and documentation maintained to support a trace-back system. This will require a 'batch code' or 'packed on' date that can link the pack of potatoes to the block from which it was harvested.
Can I sell potatoes interstate and overseas?
Requirements vary. Restrictions exist on the movement of potatoes into some Australian states and into many overseas countries. Before consigning potatoes, check the quarantine requirements of your proposed market.
Produce for export must be grown and packed on properties or in premises that have been inspected and have a registered number. Australian Quarantine and Inspection Service (AQIS) officers supervise registration of establishments. Talk to import agents from the destination country, export agents and your local AQIS officer for the latest information on export requirements.
Quality assurance
Why do I need quality assurance (QA)?
Because your customers are, or soon will be, asking for it. The driving force behind this push for quality is food safety and the fear of litigation. There have been enough instances of food poisoning or injury resulting from food consumption, for retailers and other businesses in the food industry to ignore them at their peril. Some of these occurrences have been due to contaminated fruit or vegetables.
National Food Safety Standards became enforceable from February 2001. Fruit and vegetable growers are part of the food industry and so retailers, wholesalers, processors and other handlers of fruit and vegetables have placed requirements on suppliers to ensure that the products they sell are going to be safe to eat. In future, you will probably not be able to market fruit and vegetables without demonstrating that you have an effective food safety management system of some type in place. Quality management systems provide the framework for this to be achieved.
What quality assurance standard do I need?
If you market directly to a supermarket they will tell you what you need. It will be one of either SQF 2000, SQF 1000, ISO 9002 + HACCP or a supermarket Quality Management Standard.
If you supply to a wholesaler/agent or processor, you will need to be an approved supplier to them if they want to on-sell your product to the supermarkets. The minimum requirement to be an approved supplier to a wholesaler currently varies between wholesalers, but the Freshcare Code of Practice is gaining popularity around Australia as providing acceptable food safety practices to meet the supermarkets' requirements for approved suppliers.
What is HACCP?
The Hazard Analysis and Critical Control Point (HACCP) method is an internationally recognised, systematic approach to identify, evaluate and control hazards to product specifications. HACCP relies on prevention to ensure food is safe to eat, but has also been applied to ensure customers' quality requirements are met.
HACCP was developed from the need to produce safe food for the US space program and is now widely used by all sectors of the food industry as the preferred system to manage food safety. HACCP is a key component of SQF 2000, SQF 1000 and the Woolworths Quality Management Standard. These standards require that HACCP address food safety and product quality.
What is an approved supplier program?
An approved supplier program involves suppliers carrying out practices that will provide assurance to a customer that produce is safe to eat and of acceptable quality. Suppliers need to keep sufficient records to demonstrate that the agreed practices are a part of everyday operations. The customer or someone on behalf of the customer will periodically check that suppliers are carrying out the practices.
Examples of where approved supplier programs are required:
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Growers supplying harvested produce to commercial packers and processors.
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Growers and packers supplying packed produce to wholesalers.
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Growers supplying packed produce to a marketing group.
What is Freshcare?
Freshcare is the name for a national, industry-managed program for certification of approved suppliers. It has been designed to provide independent auditing of a HACCP-based food safety program implemented by growers.
A Freshcare Code of Practice has been developed which lists practices and documentation growers need to implement in order to meet the requirements of a Freshcare audit, and so provide assurance to customers that their produce is safe to eat.
General
How do I manage cadmium levels?
In some areas of Australia, the heavy metal cadmium can occur at or above the current food standards level in potatoes. Risk factors include acidic soil; high chloride levels in irrigation water; use of phosphate fertilisers and manufactured gypsum with high cadmium levels; and low levels of organic matter.
What is the price of potatoes going to be this season?
There are two things you should not predict-the weather and the future price of potatoes. It is impossible to accurately predict prices as there are so many influencing factors.
Are green potatoes safe to eat?
No, the green section may contain naturally occurring poisons called alkaloids. Potato varieties are not released in Australia if they exceed the maximum level set for alkaloids. This rule minimises the chances of severe poisoning where green potatoes are accidentally eaten.
What causes yellow flesh in potatoes?
Some potato varieties have naturally yellow flesh, which is a desirable characteristic in many parts of the world. Yellow-fleshed potatoes have been introduced into the Australian industry and should not be mistaken as a problem.
What causes brown fleck in potatoes?
Potato brown fleck is caused by a breakdown of some internal cells. High soil temperatures and high night temperatures can both result in potato brown fleck, as can excessive rainfall or irrigation.
What causes hollow heart?
There are several causes of hollow heart. It can occur when tubers grow very rapidly resulting in internal pressure and the formation of a lens shaped internal cavity. Under cool/cold growing conditions (night temperature about 13°C) during bulking, death of tuber pith cells occurs and under subsequent warm conditions the cavity expands as the tuber bulks around the damaged cells. Hollow heart has also been related to boron deficiency.
What causes chips to blacken on cooking?
Chips blacken from chemical changes in the tuber that result in more reducing sugars. Soil conditions (temperature and moisture) also have an effect.
What causes misshapen potatoes?
Misshapen tubers (called second growth) result from uneven growing conditions including sporadic watering and high temperatures. A consistent large number of misshapen tubers over several seasons indicates the variety is probably not suited to that environment.
What is genetic engineering in potatoes?
Genetic engineering is a plant breeding technique in which a gene from another organism is introduced into the potato plant to enhance growth or resistance to disease.
DPI&F information and services
- To access DPI&F's information and services, Queensland residents can contact the DPI&F Business Information Centre on 13 25 23 for the cost of a local call. The Business Information Centre is open 8 am to 6 pm Monday to Friday (excluding public holidays); E-mail callweb@dpi.qld.gov.au. Non-Queensland residents phone (07) 3404 6999.
- Current national information on agricultural chemicals registered for use on all crops is available on the Infopest CD-ROM. Write to DPI&F, GPO Box 46, Brisbane, Qld 4001, E-mail infopest@dpi.qld.gov.au, visit the Infopest web page, or phone (07) 3239 3967 for further information.
Industry links
- Industry links is a page of links to various sites of interest to horticultural growers.
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 21 September 2005
