2 November 2009

4 minute read

Why is herbicide/ pesticide use under threat?

The contamination of water with agrochemicals and in particular, herbicides means that unless these sprays are used more responsibly their use will be severely restricted or withdrawn. Just because livestock farmers tend to use less sprays than arable farmers it doesn’t mean they should not be concerned, valuable weed control tools could be lost with negative impacts on crop yields and quality.

The main threats to the availability of herbicides and pesticides are the revision of Directive 91/414/EEC and Annex 1 approval (EU legislation associated with product safety) and the Water Framework Directive (WFD) aiming to improve water quality.

• Use of non-clover safe herbicides could result in a loss of white clover from grass leys, costing an extra £180/ ha to compensate for the lost nitrogen.

• If red clover swards are sprayed with non-clover safe herbicides, loss of yield could cost up to £550/ha in red clover leys.

• The loss of specific broadleaved weed herbicides could cost up to £95/ha in lost feed value in forage brassicas due to uncontrolled broadleaved and grass weeds.

• Reduced fungicide availability could result in decreased foliar disease control in kale, costing up to £75/ha in lost feed value.

• The loss of specific broadleaved weed herbicides to oilseed rape production would significantly reduce the amount of oilseed rape produced, reducing the availability of home-grown rapeseed meal as a protein source.

• The loss of specific herbicides in cereals would result in increased black-grass resistance and decreased yields. Combined with the loss of control in oilseed rape production this would result in decreased yields and reduced availability, or increased cost of feed wheat and barley.

• The loss of specific herbicides used in pea and bean production would reduce the ability to control grass and broadleaved weeds and oilseed rape volunteers in pea and bean crops, reducing yields by up to 44%. This would put further pressure on UK protein crop production.

How herbicides/ pesticides get into water

Storage: Pesticide stores hold concentrated chemicals; a fire or leak at the store can have a huge impact downstream.

Sprayer filling: Drips and spills of concentrated pesticides or pellets can have a big effect on water quality.

Over spray and drift: Spraying over watercourses, or too close to the top of banks, can kill aquatic life as well as jeopardising water quality. It can also concern neighbours.

Drain flow and surface run-off: Pesticides attached either to soil particles or in solution can reach water when drains are flowing or during soil erosion and in surface run-off. This is relevant on new sewings.

Cleaning: Large quantities of dilute spray solution are generated during container cleaning and sprayer washing; this can easily reach water through farm drains.

Disposal: Burying pesticide wastes in a tip is illegal and results in long term damage to water quality.

How to keep herbicides/ pesticides out of water

All watercourses should be protected with a 6m grass buffer strip, or a 5m no-spray buffer zone. All applications should be made by trained and qualified staff, who ensure that filling and all equipment cleaning takes place well away from drains and watercourses.

Herbicides/ pesticides should not be applied to dry, cracked or saturated soils or if heavy rain is expected within 48 hours of application.

Reduce the need for pesticides on grass and clover through good management

• Regular grazing or frequent cutting reduces the impact of broadleaved weeds and reduces perennial weeds like thistles and nettles; can reduce disease build up; typically disease moves in when pasture grasses get long and laid. It also controls ergot by preventing flowering.

• Maintain soil fertility to ensure grass can be competitive against weeds.
  
  
• Avoid poaching, or other damage to the sward, around gateways, troughs and trees as bare ground allows weeds to germinate.
  
  
• Check bought-in hay and straw for weeds, especially if feeding outside.
  
  

• Rotations and variety choice: Avoid growing forage brassicas in close rotations with other brassicas, such as oilseed rape to reduce club root risk. Plant club root resistant varieties (although new types of club root are starting to overcome resistance genes).

• Establishment should avoid spreading manures with high weed seed burden on land to be planted. Very rapid early growth is brassicas’ main strength. Ensure good establishment, anything which reduces this (drought, weed, pest or disease) will affect yield and increase the need for pesticides. Drill brassica crops outside of the cabbage root fly’s main egg laying period (May & June). Club root can be controlled through liming of soil (to reduce pH) prior to planting.

• General: In row crops a mechanical weeder can be used to reduce weed competition. Weed burdens that don’t affect establishment, especially grasses may be tolerated as they can provide additional green matter to be grazed. Improve drainage and reduce compaction to reduce footrots in pulses.