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 and 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.