In weed control trials this is best achieved by establishing pure populations of the required weed species in an otherwise weed free area. This allows each species to develop free from competition with other possibly more robust species. Assessments are simple because they do not require the appearance of each species to be visually differentiated from the overall appearance of a mixed weed population. This permits assessments to be carried out rapidly, accurately and reproducibly by less skilled personnel. The same advantages apply to the use of lines of pure species to enhance the impact of a demonstration.

Compact field screens permit the performance of a new herbicide to be characterised on a large number of species, using a small area and small amounts of chemical. Sow lines of each desired species 20 centimetres apart, thus producing a bed containing five species per metre of width, and as long as is necessary to provide the desired number of treatment plots. Apply each experimental treatment across the width of the bed.

A criticism of the sowing technique outlined above is that because all seeds of a species are sown at the same depth, seedling emergence occurs over an unusually short period. For a greater similarity to agricultural practice the following procedure is effective:

1] prepare the seedbed

2] mark out the plots

3] scatter the weed seeds from a bucket by hand in 30cm. wide bands. Make one band of each species, 30cm apart across all plots

4] if desired, plant the crop over the whole area

5] harrow to a depth of 5 cm and roll

6] apply treatments at right angles to the weed rows.

The harrowing operation distributes the seeds in the top 5cm of the soil, resulting in a protracted seedling emergence similar to that of a natural weed population.

The following table describes the season at which seed of the most widely used temperate arable weeds can be sown, its optimum depth for establishment and provides additional comments which may be helpful to the trials worker.

Many spring weeds will germinate in early autumn but their seedlings are killed by the winter frost. However these species can be sown after mid October, whereupon the seedlings emerge in early spring. Sowing in late autumn or winter is particularly valuable for seeds which require a cold period to achieve maximum germination. Alternatively seeds of such species as Polygonum, Aethusa, Atriplex should be stratified prior to sowing in the spring. Stratification involves mixing the seed with three times its volume of coarse sand or vermiculite, moistening to field capacity and storing in an open container at 0-4 Centigrade for 3 weeks to 3 months. A detailed proceedure for stratification is given in 'Herbiseed Brief Weed Guide No. 2'.

In the following table,

A.= Autumn sowing

W.=Winter sowing

S. =Spring sowing

Depth = depth in millimetres of soil cover

SS = Surface Sow with no soil cover. This requires continued surface moisture.

Scarification = thoroughly scratch seed coat with sandpaper to permit imbibition.

TRIALS ESTABLISHMENT

GRASS WEEDS

Herbiseed, New Farm, Mire Lane, West End, Twyford, RG10 0NJ, England.
Tel: +44 (0) 1189 349 464  Fax: +44 (0) 1189 241 996  e-mail:[email protected]