Weed control in bale silage

UK - March 14, 2011

Perennial broad-leaved weeds such as docks can significantly affect the quantity and quality of grass harvested for silage.  They can be controlled well by spraying with a translocated herbicide at least three to four weeks before cutting. Follow label guidelines on rates, water volumes and timing of application to optimise results.

Research at the Institute of Grass and Environmental Research (IGER) showed that a 20% infestation of docks in a silage crop can reduce grass yields by 20%. So for a field that normally yields 11t DM/ha/year, as much as 2.2t/DM/ha could be lost each season.

With silage costing 10p/kg (12 cents/kg) DM to produce, this means each hectare of grass can earn an additional £220 (260 €) in extra feed when docks are controlled, compared to fields where they are left to grow. With rapidly rising cereal prices, maximising the amount of silage produced from grassland has never been more vital.

Docks are also less digestible than grass and will pull down the feed value of any resulting silage. This means more, costly supplementary feeds will have to be bought in to supply the required nutrients for livestock, than if the silage was weed-free.

An added problem when baling silage with docks in is that their tough stalks can easily puncture the plastic wrap – allowing in air which will affect the fermentation, creating potentially dangerous moulds and unnecessary spoilage.

Controlling weeds
Several herbicides can be used to control weeds in grass silage crops. Products based on traditional phenoxy chemistry such as MCPA and 2,4-D offer a short-term, above-ground solution, but re-growth is likely from roots or underground stems.

Newer, translocated products, such as Doxstar, which get right down into the roots of the target weeds, do a better job over a longer period. Also they will not hold back grass growth. This was confirmed in the IGER trials which demonstrated that there was no reduction in yield from spraying grass with this type of product.

Follow spray guidelines
To extract maximum benefit from an investment in spraying with herbicide, producers should follow a few key principles. Grassland herbicide manufacturer Dow AgroSciences has developed the PRIDE guidelines to help contractors and farmers with their weed control.

Product - Use the right product for the target weed.

Rate – Apply the correct rate of product in the appropriate water volume. The rates have been carefully tested and calculated by the manufacturer for optimum control.  As much of the cost of weed control is tied up in the labour and machinery used to apply the spray – it pays to do a proper job once.

Similarly skimping on water volumes is false economy – particularly when spraying in established grassland where grass can shadow a high proportion of the weed plant. Use at least 300 litres of water/ha, and up to 400 l/ha in thick swards, to get as much chemical as possible onto the weed leaves.

Information – be aware of planned cutting dates and post-treatment use. Allow at least three weeks, preferably four, between application and planned cutting date. This allows enough time for the herbicide to be carried deep into the roots before the leaves, which have an important role to play in driving the transport of chemicals around the plant, are removed by mowing. Timing can be quite tight when treatments are applied between first and second cut.

Density  -  Consider the size of the infestation. If docks make up more than 5% of the field, a broad-acre spray will be cost-effective. For best results, translocated products should be applied when the weeds are actively growing and at the perfect stage for spraying – not too little, not too big. Docks should be at rosette stage up to 25cm high or across.

Environment - Consider the state of the target plants before spraying as well as the wider environment in which the weeds are growing.

For best results, weeds must be healthy and free from disease and insect attack and not suffering stress from drought, frost or water-logging. This allows the spray to be taken and transported around the plant for maximum effect.

Herbicides should always be used with due regard to the environment and at the correct distance from watercourses ie never spray within one metre of the bank. Read the label for product specific advice.