Many of the world’s most serious weed problems have arisen through accidental or deliberate importation of seed. Resistance to herbicides has arisen in some weed species in limited geographical areas, often as a result of continuous repeated use of individual or related groups of herbicides. Outside these areas the herbicides continue to be effective against these species. It is essential that resistance is not introduced into Great Britain by the careless handling of seeds and plants of resistant biotypes. Such unwanted introductions could have considerable consequences for the agricultural industry.

A. SUPPLIERS OF SEED OF RESISTANT BIOTYPES

Suppliers must keep a record of the purchasers of resistant seed.

Suppliers should provide the customer with a code of practice for handling such material and ensure that the customer acknowledges and understands this code (see below).

B. USERS OF SEED OF RESISTANT BIOTYPES

Wherever possible restrict investigations to laboratory or glasshouse.

Take all possible steps to prevent accidental escape of resistant plant material by paying great attention to experimental hygiene as published below.

If ‘field’ studies are unavoidable the following guidelines must be followed even more closely than with glasshouse studies.

Live plant remains should be destroyed before disposal (e.g. with herbicides, by burning, by sterilisation).

The contamination of soil with dormant seed and other viable propagules must be avoided. If contamination occurs soil affected must be sterilised.

With outbreeding species, the spread of pollen from resistant biotypes to native susceptible ones must be prevented by the use of screens.

Surplus seed must be burnt.

Herbiseed, New Farm, Mire Lane, West End, Twyford, RG10 0NJ, England.
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