Ware Potato Production
Ware, or eating, potatoes are a traditional crop in Northern Ireland, and are of potential interest to many organic producers because:
- There is good interest from consumers, and producing quality crops can be profitable
- Potatoes provide a break crop from grass/clover leys in the rotation
- Cultivations for potatoes provide opportunities to control weeds
- Organic potato production can fit into a planned rotation on many organic units
A common misconception is that consumers of organic produce will accept a lower quality of produce, because it is organic, compared with conventionally grown produce.
This is generally not true and potatoes presented for sale should be of the highest quality, and on a par (visually) with conventional produce. Multiple retailers will set very high standards and reject unattractive samples.
Consumers, initially at least, often buy potatoes based on appearance, and placing poor quality produce on sale will have an adverse impact on consumer acceptability and purchase. It may also damage the prospects for future sales however good the actual or apparent cooking quality.
Important aspects of husbandry
Modern conventional (non-organic) potato production is a highly technological operation utilising specialised machinery and pesticides.
Organic potato producers are restricted in the techniques they can use, and have to rely on alternative approaches and technologies rather than artificial fertilisers and synthetic chemical herbicides, insecticides and fungicides.
- Growing at the right point within a planned rotation
- Planting healthy, disease-free seed
- Providing additional nutrients through organic manures and slurries
- Mechanical and other non-chemical weed control
- Pest and disease control without modern pesticides
- Blight control with only limited, controlled, specified fungicide application
Organic standards lay down specific rotational requirements for potatoes, and a rotation of one year in four is probably the minimum acceptable to organic control bodies
One of the main reasons for this is to avoid the build up of Potato Cyst Nematode (PCN), also known as ‘eelworm’. See later for further guidance on eelworm control.
Selecting potato varieties
In selecting varieties for organic production there are two simple rules:
Grow varieties suited to organic production, particularly those having good blight resistance
Grow varieties which best suit the intended market
As with all organic produce, meet the needs of your market by growing what you can sell, not what you want to sell.
Sourcing seed potatoes
Organic potato crops must normally be grown from organically produced seed potatoes. The COSI organic seeds database (www.cosi.org.uk) shows sources of organic seed potatoes.
Derogations for planting non-organic seed are now difficult to obtain.
When ordering seed :
- Order seed early (even whilst the seed crop is still growing) to ensure supplies
- Plant the highest class of seed you can afford, preferably a higher Super Elite (SE) class
Seed storage – before and after purchase
- Ensure seed has been correctly stored prior to delivery so as to prevent development of storage diseases and sprouts in store
- Unless you have good seed storage facilities, leave seed delivery as late as possible
- After seed has been delivered, preferably place it in a temperature controlled seed store, or at the very least store as cool as possible to prevent excessive sprouting
To produce high quality potatoes with good skin finish and minimal damage a fine, stone and clodfree seedbed is required. Particularly on land containing stones, the best way to do so is to use a stone and clod separation system following ploughing. Most growers employ a specialist contractor for this, and most multiple retailers will insist on stone separation.
Some growers are concerned that on heavy land this can be difficult, but is must be emphasised that stone and clod separation should be carried out when the ground is in the right conditions. It should not be done when the ground is wet.
Potato Cyst Nematode (eelworm) control in organic ware potato crops
PCN is a microscopic worm that invades potato roots to feed, and at large infestation levels a noticeable yield reduction occurs, generally along with yellowing and wilting of foliage.
Land which has been ‘scheduled’ due to PCN infestation in the past may not be used for growing potatoes.
If you are unsure as to whether there is PCN present in a field, DARD recommends an ‘advisory’ test, available through DARD Agriculture Development Centres, particularly if older varieties susceptible to PCN are to be grown.
Advisory sample analysis is carried out by the Agri-Food and Biosciences Institute, (AFBI).
At present PCN levels in ware ground are very low and a one year in five rotation, or longer, helps to maintain this.
- PCN occurs as several races of two species; Globoderarostochiensis and Globoderapallida
- Many older potato varieties are very susceptible to PCN attack
- Many newer varieties have at least some resistance to PCN
DARD approach to PCN control in organic ware crops
- Have fields tested for PCN presence (advisory test) and PCN species
- Try to maintain a rotation of one year in at least five years (one in four minimum)
- If at all possible do not grow on fields with PCN present
- If PCN is present at low levels, only grow an appropriate resistant variety
- Only plant certified seed
- Avoid transfer of PCN from infected to non-infected land by ensuring boots, machinery and tractors are well cleaned between fields
- Do not dump soil and potato waste on fields likely to have potatoes grown in them in the future
Growers should note that :
- Ware crops may not be grown on land scheduled under seed potato legislation
- Fields tested for PCN for uncertified ware crops will not be scheduled if found to have PCN from an advisory test
- Subsequent intended production of a certified crop (seed or ware) in such fields will still require a statutory PCN test as at present.
Providing crop nutrients
In organic production, provision of specific amounts of nutrients is not generally possible.
It is highly likely that an organic potato crop will be grown as the break crop following a grass/clover ley which will provide significant quantities of nutrients, particularly nitrogen.
Alternatively, potatoes can be grown following a legume crop or a leguminous green manure.
Because potatoes require a large quantity of nutrients, manure should also be applied at this point in the rotation.
After blight prevention, weed control is potentially the most troublesome field operation facing organic potato producers. As no herbicides are permitted, weed control is carried out by:
- Choosing fields which have no major weed problems
- Flame weeding of weed seedlings before the potato tops emerge
- Mechanical removal of the first flush of weeds whilst they are still small
- Mechanical weed removal just before tops meet between rows
- Limited hand weeding of any large invasive weeds
Pest problems are usually fairly intermittent in potatoes. There are currently no Approved pesticides for organic potatoes.
- Planting healthy, disease-free seed is the key to disease control
- Try to buy seed from a producer who has a proper seed drying and curing system, along with refrigerated storage
Preventing potato blight
Potato blight cannot be cured and, particularly in an organic situation, avoidance is definitely the best policy.
Certain fungicides are currently permitted, under prior derogation, and must not be applied on a routine basis.
- Blight is not generally a problem with early harvested, early varieties.
- Plant early varieties if suitable/possible
- Plant healthy, blightfree seed
- Select varieties with high blight resistance
- Use a blight risk monitoring service such as DARD’s Blight-Net
- Listen for, and pay attention to, blight warnings
- If the blight pressure is high apply a permitted fungicide
Under Northern Ireland conditions organic potato producers frequently have to remove potato haulms early because of foliage blight. This reduces yield but helps to avoid tuber blight.
Revised EU Organic Regulation on copper use
The EU has accepted that copper fungicides are indispensable in organic production in the medium to long term, and their use is “authorised for the time being”.
This may be reviewed at any time, in the light of new developments and evidence with regard to viable alternatives.
Limits have been set on the quantity of copper (not product) which may be applied per hectare per year.
This is currently 6KG unless it can be demonstrated that for individual crops this is not efficacious.
This limit has implications for the maximum number of spray applications which may be applied.
What products are available ?
Only commercially approved pesticides may be used, and use of home-made versions of sprays such as Burgundy and Bordeaux mixture is illegal and against organic standards.
There are four commercially available copper-based products approved for use in the UK as formulations containing either copper sulphate (as Bordeaux mixture) or copper oxychloride.
If you use a range of products beware of exceeding the copper limit. Keep uptodate, sequential records of total copper application.
|Approved product||Manufacturer||Copper content||Product application rate|
|Wetcol 3||Laws Fertilisers||30 g/l||50-90 l/ha in 1000 litres of water|
|Cuprokylt||Unicrop||50% w/w||5.5-6.5 KG/ha|
|Cuprokylt FL||Unicrop||270 g/l||5.5-6.5 l/ha|
|Headland Inorganic Liquid Copper||Headland||250 g/l||10 l/ha maximum|
How should I use any product ?
When wishing to apply a fungicide a number of very important points should be noted :
- Control bodies may vary in the fungicide products which they permit
- Prior permission (derogation) is required, for each and every proposed application
- Only use approved proprietary products, as home-made formulations are not allowed under the Food and Environment Protection Act 1985 (FEPA) and the Control of Pesticides Regulations 1986 (COPR)
- Routine fungicide application is not allowed
- Some products are not approved for first early or seed crops
- You should consult your standards so that you fully understand how your sector body has interpreted the legislation
With a very limited number of applications possible, careful monitoring of blight risk is essential as a means of assessing whether or not a fungicide should be applied.
All of the products available are ‘protectants’ operating by preventing blight spores landing on foliage from ‘germinating’. They tend to be relatively easily washed off leaves, and it is accepted that blight control may not be as effective as more modern products which organic standards do not allow.
Blight warnings and decision support systems
DARD provides several sources of information giving warnings about the presence and risk of blight infection
- Blight line Tel: 028 9038 2372
–answering machine based blight information service
- Blight net www.ruralni.gov.uk/index/crops/potatoes/blight_net.htm
-DARD’s blight control decision support system indicating blight risk
If fungicidal control fails
If only a few plants are infected, lift them immediately into plastic bags, seal and remove from the crop. The aim is to stop further spread and prevent spores washing down onto tubers in the soil.
If more than 50 blight spots per plant are seen (five percent blight), and the whole field is affected, then tops should be removed as soon as possible. Under organic management this usually means using a haulm chopper. Do not chop foliage when it is wet or you risk spreading blight spores everywhere.
What else can I do ?
If you cannot control blight on foliage then there is little else you can do in that season.
You should however, aim to avoid taking blighted tubers into store or marketing them.
To avoid taking blighted tubers into store :
- At the time of haulm removal, and a week later, inspect a sample of tubers from across the field carefully
- If blight is found the crop should be left in the ground for several weeks until blighted tubers rot and ‘melt’ into the ground.
- Once the crop in which blight has been found has been harvested, inspect the crop frequently for signs of further tuber blight and market it quickly, ensuring all blighted tubers are removed
Some potato growers have their spraying carried out by a contractor.
Check very carefully with your control body that they will allow this and, if so, take great care to ensure that sprayers are cleaned out thoroughly before being used on organic crops.
You may be required to dedicate a sprayer for organic use.
Haulm destruction, harvesting, storage and grading
Only physical means of haulm removal are permitted. These include :
- Flailing (haulm chopping)
- Haulm pulling
Chemical methods of desiccation or application of sulphuric acid are not permitted
Haulm destruction should be carried out as soon as the crop reaches marketable size. This will probably occur from mid-August onwards.
Do not wait, unless weather conditions are unfavourable.
Do not flail/chop haulms if they are wet as this can spread blight.
Allow two to three weeks for skins to set before harvesting, checking that they have set before you start.
Avoid harvesting when the soil is very dry or very wet.
Correct storage will ensure that crops are available in good condition for a long period.
For short-term storage, store at around 7C, though at this temperature sprouting will occur sooner or later, depending mainly on the variety. Circulation of ambient nighttime air can often be used to provide these conditions.
For long-term storage provide cool dry conditions at around 3C. This will stop sprouting and disease development, but requires expensive refrigeration and a well-insulated store.
Two alternative techniques can be applied to crops as they come into store depending on the condition of the crop.
1. Dry curing
Blow or suck warm air at 12-15C and at a controlled humidity of 80 percent through the potatoes, for about two weeks, to encourage wound healing at. Forced ventilation and dehumidifying equipment are required.
Wet crops should not be dry cured, but should simply be dried with cool air.
Then progressively lower the storage temperature down to around 3C or 7C as appropriate to the required storage period.
Dry crops, if required, by forcedair ventilation with cool air.
Then progressively lower the storage temperature down to around 30C or 70C as appropriate to the required storage period.
Grading / sorting
Before grading, potatoes should be allowed to warm up to around 100C to avoid bruising. Cold potatoes bruise very easily.
Be very careful to grade out all damaged and diseased tubers so as to present a high quality product.
Use of contractors
Many growers nowadays employ contractors to carry out the specialised potato growing operations which require expensive equipment.
It is essential that contractors’ machinery is thoroughly cleaned before it comes onto organic land, to avoid bringing soil, pests, diseases and chemicals onto the farm.
Seed potato production
Whilst this leaflet has dealt with growing ware potatoes, there is clearly potential for organic seed potato production in Northern Ireland since organic ware producers require organic seed.
It is, however, a specialised task, made more challenging by the restrictions organic standards place on keeping crops free from disease.
© CAFRE - December 2010