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RESEARCH > CASE STUDIES AND REPORTS > REPORT T00

Report T00 *****

Problem: Spear Thistle in pasture
Where: High Cross Field, Hill Top Farm, Spaunton, North Yorkshire
When: February, March 2002
Status: Organic
Area: 4.65 hectares(11.50 acres)
Detail: Trial, during which we removed 8016 rosettes in 18.23 man-hours. (After F & M restrictions)

click map for larger version

Known cause of problem: wind blown seed from an adjacent field to the north, followed by 4 months winter grazing of sheep (enforced by F & M restrictions).

ASSESSMENT: the trial showed how the ‘RIP’ method can be efficient when applied to problems in grassland. Before work started, the field was tram-lined, using the wheel markings of a light van. These made visible divisions for each operator to work in, and they were spaced about two metres apart. Sometimes, when one strip had a far greater number of plants, the whole team would all help to clear that area. The work was carried out by four members of the available farm workforce (including a 14 year old), and broken into four separate visits to the field. The 3 hrs allowed for ‘follow-up work’ in June, were probably less than recorded. All Spear thistle plants had been removed by the time Hay was taken from the field in July,

See more conclusions and comparative costs of other solutions, below. J.Trevelyan BSc. Aberdeen.2002.

Refer to drawing, page 3

Trial conditions : Young plants in moist ground (rosettes between 3" & 8" across),.

  • Total plants in seriously infested area ‘A’ ( 3.0 acres) = 6260

[Average Density = 16 plants per 25 sq.m.]

  • Total plants in lightly infested area ‘B’ ( 8.5 acres) 1756

[Average Density = 1.20 plants per 25 sq.m]

  • Work-rate (weeds removed per man-hour) overall = 439 rosettes per hr.

Work-rate in seriously infested area ‘A’ = 576 rosettes per hr.

Work-rate in lightly infested area ‘B’ = 232 rosettes per hr.

Results:

  • Total number of seedling & rosette weeds extracted : 8016
  • Duration of work : 4 visits during 4 days.
  • Total man-hours worked : 18.23.
  • Initial Clearance Costs : @£7 per hour = £126.
  • Follow-up costs : £21. (3 man-hours).
  • Total Workforce costs : £146. [ £12.69p. per acre / £31.3p per hectare].

Comparative Costs of Boom / Spot Spray / Weed-wiper solutions.

Boom Spraying costs:

Basic chemical costs to kill Scotch thistle in pasture are about £2 per acre.

More selective chemicals are more expensive.

Application costs vary with total area sprayed in the contract. These could be as little as £3 per acre for 50 acres (or £7 per hectare), or doubled on smaller areas.

Distance from contractor base, and ease / cost of water access all contribute.

A quote from R.Strickland & Son (contractors 3.5 miles distant to the trial site), came to more than £110, because of special rates for a relatively small acreage & a ‘least damage to clovers’ mix of chemical. That’s £9.56 per acre or £23.62p. per hect.

Spot-spray costs:

Application work-rates are very similar to those of ‘RIP’ (number of plants dealt with per hr.). Added to those costs, are the price of chemicals and the time it takes to mix and refill the knapsack. These would bring the total cost of spot treating 11.50 acres to at least £200. There are many other restrictions & disadvantages, which cost money. These are listed in a L-D document titled The Removal of Individual Plants’ (see website).

Weed-wiper:

The height of weeds has to be greater than the crop, so the field must be well grazed. The land must be reasonably level. Contractors should, but do not always take into account all costs:

Capital Costs of machinery

Operational Costs of obtaining & mixing chemical, fuel, & maintenance

Some other considerations:

Drift of both spot & boom spraying, & damage to soil fungus, bacteria & clover.

Time waiting for correct weather conditions (phone- calls, delays).

Time for removal & replacing of stock ?

Time for collection & delivery of chemicals (& transport miles)

Time for filling in records / safety clothing etc.

Boom spraying, paricularly in areas of ‘low weed density (eg. Zone A in our trial) is absurdly costly ( and damaging).

Assessment of High Cross Trial.

A large number of rosettes were pulled efficiently, and the field was cleared.

Costs indicate that the ‘RIP’ method was applied correctly. Comparisons with chemical solution costs are remarkable. Why was RIP so successful and why was the work rate so high ? There are four main reasons:

  1. Weed rosettes were often no bigger than 2" or 8" across, which meant that they could be dug out easily, and piled onto the end of the grubbing noses, with little need to kick them off individually (they accumulated & tumbled off).
  2. The land was still winter-moist to full depth of bigger rosette roots.
  3. The task was broken up into 4 separate visits, which meant that the workforce never became tired.

4) The workforce was available, and had learnt the knack of using the tools.