Last week’s lift in weather resulted in a hive of field work activity as farmers moved to try and catch up on tasks prevented by the challenging spring. Sluggish grass growth rates throughout April allowed weeds to become established in many grassland swards with these weeds becoming much more prominent with a spike in growth rates over the last week to 10 days.

The recommended height for spraying thistles in at a height of 200mm or 8".

Optimum treatment of weeds is all about timing. Addressing issues now can deliver a significant lift in performance this season and in subsequent years. The four worst offenders are generally docks, thistles and nettles, while rushes is a significant problem on more marginal lands.

The optimum timing for treatment of weeds such as thistles, docks and nettles is what is known as the rosette stage. For docks and nettles, this is when plants are at a height of about 150mm to 250mm or 6in to 10in.

Optimise spray

The growth pattern of thistles is slightly different in that leaves grow outwards quicker. This allows greater potential to optimise spray coverage at a lower height with the best time to control thistles recommended at approximately 200mm (about 8in) in height.

In addition to maximising spray coverage, weeds at this height will typically be growing at their most active. This will encourage chemicals to be taken in and transferred around the plant quicker. If weeds have not reached this stage, then the advice is to delay treatment.

This may not be possible in silage swards that have been closed early. If this is the case, a decision will need to be taken on temporary treatment or possibly spot-spray treatment. Spot spraying is also likely to be a more realistic option where weeds are present in isolated cases and the aim is to keep on top of them and stem their spread.

Time of application

It goes without saying that spraying should not take place on a windy day or where there is a risk of spray drifting.

Where spraying is carried out while sunshine is strong then water droplets falling on the leaves will act as a magnifying glass

The optimum conditions are on a dull day. Where this is not possible, spraying early in the morning or late in the evening should be the target during periods of high daytime temperatures or sunny weather.

Where spraying is carried out while sunshine is strong then water droplets falling on the leaves will act as a magnifying glass. The sun’s rays can burn and damage the surface of the plant which, in turn, can reduce the ability of the plant to absorb chemicals.

Herbicide choice

There are numerous herbicides on the market that are formulated to target one particular weed or a combination of weeds. It is important to consider your choice and select the weed that best addresses the greatest challenge.

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There can be a temptation when spraying grassland swards to mix sprays with the aim of covering a greater number of weeds than would otherwise have been possible with the one application.

Where docks are at an advanced stage or are isolated in swards then spot treatment may be an alternative option.

Examples of this include mixing sprays that have a hormonal mode of action (such as MCPA, CMPP or 2.4-D) with sprays which have a systemic mode of action (such as Dockstar, Pastor, etc).

This is advised against as sprays with a hormone mode of action work quicker on the plant and begin to shut it down immediately. As the plant begins to shut down, movement of the systemic herbicide that is fully translocated down to the roots will be limited and the herbicide will not get a chance to work into the root system. This will hamper the success of the treatment and risk your investment being lost.

Sprayer or weed licker?

A weed licker will generally not achieve as successful a kill as spraying. The area of the plant which comes in contact with the herbicide will influence the success of the kill and this is usually best achieved by spraying.

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Weed lickers are usually mainly used when weeds are at a set height above grassland.

Treatment at this stage will bring about a limited kill

Weeds at this height are usually mature or gone beyond the optimum stage recommended for treatment. Treatment at this stage will bring about a limited kill and will generally not prevent weeds from re-emerging.

Fact or fiction

Many people often comment that applying slurry on pasture spreads docks, with the insinuation that dock seedlings are spread via slurry.

Dock seedlings do not survive where silage fermentation is adequate and silage is preserved optimally or where it passes through the rumen and into slurry. The reason why docks often prosper where slurry is applied is due partly to the fact that slurry is generally applied in silage swards that receive a high annual nitrogen input or on the same lands from year to year.

Docks thrive in high soil nitrogen conditions and hence this is usually the reason why they prosper where slurry is repeatedly applied.