Growing crops for seed is a highly specialised job. Seed grain or potatoes have to be grown to the highest standards to obtain official certification.

They have to be free of disease or weed seeds, and the purity of the variety has also to be guaranteed. After all, if you plant Duke of York potatoes you would be upset to see Epicure or Kerr's Pinks growing as well.

Producing seed to such rigorous standards is very expensive, but can also be very profitable if done properly.

During early summer highly-trained officials from the Department of Agriculture and Fisheries for Scotland (the Department) inspect seed crops to certify them as fit for seed. For instance, an inspector is able to recognise at least 40 major potato varieties, as well as identify all of the major varieties of barley, wheat and oats - a total of about 70 cereal varieties.

Before the inspection farmers "rogue" their fields of cereals and potatoes being grown for seed. Roguing cereals is relatively straight forward and involves a small squad walking backwards and forwards through the crop removing unwanted plants such as wild oats or maybe black-grass, that tend to stick up 6 or 7cm above the crop. All rogues are put in a haversack and dumped at the edge of the field to be destroyed.

You would be amazed how rogue plants can hide themselves. A gust of wind can cause the head of a wild oat or volunteer cereal plant, such as barley in a field of seed wheat, to duck down among the main crop. Only when you are 50 metres up the field will it spring back up to laugh at you.

Roguing crops of potatoes intended for seed also involves small squads, but is a much more skilled job with real responsibility that requires training. It is ideal for those keen on spending the summer outdoors and qualified roguers can earn £10-£15 per hour, depending on experience.

The SRUC (Scotland's Rural College) is to hold a five-day course on potato roguing at Craibstone Campus in Aberdeen from 18-22 June. It costs £375 but part-funding is available for some applicants through Skills Development Scotland.

The course includes instruction on the identification of varieties of potatoes, virus diseases and variation of potatoes as well as the Department's Inspection Scheme, with all grades and standards required.

SRUC's Michael Coutts, who runs the course, said: "We teach 20 of the top varieties by area grown for seed and bring in new varieties to replace the declining ones each year.

"We plant beds of each variety and also beds with each disease we have for the healthy varieties on the course that year. A row of each disease we have seed of is grown next to each other so students can see what the symptoms are compared to the healthy row."

The first two days of the course are spent doing variety and disease descriptions to get the student's eye trained to see the difference in how the leaves, stems and buds look between varieties and with disease on them.

The next three days are mainly spent doing tests on rows of plants where all the varieties and diseases are mixed up.

Those interested in doing the course should email:

Tom Maxwell, Senior Communications Officer at SRUC, who spent four summers potato roguing as a student (1999-2002) said: "When I did the course at SRUC's Elmwood campus in Fife. I remember our course instructor having a particularly poetic flair for helping us to recognise the different characteristics, or "habits", of each potato plant. Even after all these years, I still remember things like Maureen is "blue-green" and to think of Lady Rosetta's leaves as like a posh woman's jewelry. Maybe not conventional, but it helped you remember.

"The job itself can be hard work with long hours, but the money is good and there's plenty of fresh air and exercise. You certainly never forget your first encounter with a plant that has blackleg - the smell of the slime takes a couple of days to wash off."

Seed potatoes produced and marketed in Scotland must be classified under the Seed Potato Classification Scheme. The certifying authority for this is SASA (Science and Advice for Scottish Agriculture), a division of the Department.

Once rogued, a Department inspector will select a sample area of the potato crop at random for inspection, to see if it is good enough to be certified for seed. Their trained eyes miss nothing, and that's when all the missed rogues stand up to be counted.