Varieties of field vegetables and potatoes for organic production and marketing OF0304

Summary

The objectives of the work were to investigate the suitability of selected varieties of vegetables and potatoes for organic production using organic or untreated seed on certified organic sites.
Organic growing of vegetables and potatoes imposes restrictions on the treatments which growers can apply to crops to maximise yield and maintain quality. Hence choice of variety is more critical in organic situations than for conventional crops where problems can be solved at a later date by application of pesticides or fertilisers. Varieties are needed that can respond to the sometimes sub optimum conditions that are imposed by the restrictions of organic systems and identification of these are not always evident from trials under conventional conditions.
In addition, variety choice may be restricted for organic growers as they are required to use organically produced seed of a variety where it is available. Derogation allows the use of untreated conventional seed where suitable varieties are not available organically.
This project tested:
 available organic seed as much of it has not been evaluated in any UK trials
 untreated seed of varieties in production for organic seed
 attempted to identify varieties of conventional seed that would be useful in organic systems so that organic seed can be produced.
In this 3 year period trials were carried out on leeks, cabbage, celery, broccoli, lettuce, cauliflowers, carrots and potatoes. Varieties were assessed for yield, quality, pest and disease resistance and shelf life and storage where appropriate. Seed health was also checked to ascertain levels of seed borne disease.
Results from these trials;
Leeks
Leeks were reasonably easy to grow organically. In our trials the main problems were weed control and leek rust infection although there is also the risk of thrip and White Tip infection. In some of the trials there was also an obvious nutrient shortage. A wide range of varieties is available differing in maturity, shank length disease resistance and winter-hardiness. In general the requirements of organic leek growers closely match those of conventional growers. Very few hybrids are available as organic seed.
Cabbage
2001 to 2003 trials included a wide range of types. As for other brassica crops aphid infestation and speed of development were the most important factors in discriminating between varieties. In general smooth varieties were less affected than blistered varieties, early maturing varieties less affected than lates and red varieties less than green or white types.
Celery
Organic celery needs to be grown on water retaining soils and given adequate irrigation. just like the ICM crop. The biggest problem for the crop is Septoria, which can devastate plants very quickly. Starting with clean seed is essential but air-borne infection can come in from infected crops or debris. Giving plants better airflow from wider spacings or bed systems seems to delay infection. Slugs can also cause problems and data on both these problems was recorded and included in the published results.
Broccoli
Growing organic broccoli trials presented similar pest problems to other brassica crops in that cabbage root fly has to be avoided at establishment and aphid and caterpillar attacks later on. Fleece was used on all early trials but in later years it was not used to allow for easier weed control. Broccoli was fairly competitive with weeds and some recent trials were only hand weeded once. Fertility seems to be a problem and we did not achieve heavy crown weights.
Lettuce
A wide range of types of lettuce are important for organic growers and this series of trials included butterhead, crisphead, Batavian, Cos, Little Gem and leaf types. Vigour, flavour, disease, pest and tipburn resistance are all important characters for a successful organic variety. Fortunately there are more genetic pest and disease differences available in lettuce than for most other vegetable crops. In addition a large number of varieties are available as organic seed.
Cauliflower
Three maturity periods were sampled i.e. summer, late autumn and Spring Heading. Aphid and caterpillar damage were major problems and there was some evidence of varietal differences in susceptibility. When conventional trials with similar varieties were grown from the same planting dates the organic varieties were slower to mature. This may have been because nitrogen was more limited. Very few varieties of cauliflower are offered as organic seed and growers would struggle to find a good continuity program.
Carrots
The 2001 to 2003 trials concentrated on main crop varieties. A successful organic carrot variety needs most of the following: good early vigour to emerge quickly and compete with weeds, rapid bulking to compensate if late sowing is used to ovoid first generation carrot fly, large top for weed suppression and any pest or disease resistance available. Several mainly hybrid varieties performed very well in these trials.
Potatoes
Good seed quality is a fundamental in the production of a quality crop. Chitted seed will encourage rapid emergence and aid in better weed control and earlier bulking leading to bolder tuber samples. Variety selection should be made for rapid establishment, good ground cover, early bulking yield potential and a good resistance to pests and diseases, especially late blight. Sharpo Axona and Sharpo Mira had outstanding blight resistance.
Shelf Life
Shelf life depended on the health of produce tested. If healthy clean material was tested results were similar to those of conventional vegetables. If there was disease or pest damage at the beginning of a shelf life test then produce tended to deteriorate more quickly.
Seed Health
Seed borne disease levels were checked by the OSTS. In general brassicas were reasonably clean but some carrot and celery seed lots had high levels of Alternaria or Septoria infection.
All trials were reported as NIAB One year results and also made available on the COSI web site: www.COSI.org In addition, data for over 400 varieties was summarised and published in the NIAB Organic Vegetable Handbook.