Talking Agronomy with Chris Martin: Getting the most from residual herbicides

Article taken from Arable Farming, October 2017.

 

Warm soil temperatures and plenty of moisture across the region gave oilseed rape crops the best possible start. However, as predicted, slugs have been a real menace in some fields, to the extent where some patches have been redrilled. Flea beetle has been a bit more variable, being a real issue in some fields, but absent in others.

Pre-emergence herbicides appear to be working well. However, due to the speed of germination, these were missed in many fields and, as weeds also germinated quickly, post-emergence residuals will have their work cut out. As such, the addition of the contact herbicide Parish [phenmedipham] to our armoury this season could be useful, particularly in areas where pre-ems have been missed and weeds are established.

While Parish is not a stand-alone herbicide and should always be part of a programme, it fits in where residuals have either failed, have been missed, or as a precursor to the likes of Clearfield or Kerb [propyzamide], preventing key weeds getting too big and competitive. To get the best activity from Parish on several difficult weeds, it is vital to spray on bright, sunny days when crops are actively growing as it works by inhibiting photosynthesis.

Companion plants in oilseed rape have also established well and the synergy between berseem clover and better rooted OSR can already be clearly seen. As a word of warning, it is worth checking with your seed merchant which variety of berseem clover you drilled as one type on sale was not designed as a companion plant for OSR. Not only can this bring in unwanted early competition to the developing OSR due to its more prostrate growth habit, but as a multi-cut type of clover, it is unlikely to be naturally removed over winter and will require a spring application of clopyralid to control it.

The heavy rain in early September played a valuable role in preventing early drilling of cereals. The showers also helped with grass-weed flushes, so stale seedbeds should be effective this year.

With residual herbicides increasing in their importance in the battle against grass-weeds, seedbeds have never been so important. It is vital to get good seed to soil contact but also to ensure the seed is consistently covered with up to 40mm of soil to minimise crop damage as we stack more residual chemistry pre-emergence. Application is key to get the most out of residual chemistry and it is vital we 'paint' the soil. This requires maximising the number of droplets hitting the target and is best achieved with a higher water volume while maintaining as fine a spray quality as possible.

Performance

For many years, twin lines or twin caps angled forwards and down have performed best. The addition of an application aid, such as Remix, is also now essential as it can greatly improve the performance, crop safety and environmental impact of residual herbicides.

This firstly reduces drift by optimising spray droplet size, reducing the number of the smallest droplets. It is also able to maintain fan angle across a greater range of pressures, ensuring more even deposition. Additionally, the long polymer-chain formulation gives it a positive charge, allowing it to bind to colloids in soil, keeping the product in the zone of activity for longer, improving performance, reducing crop damage from residual chemistry and minimising leaching into watercourses.

Agronomist facts


Chris Martin is a technical manager for Agrovista, based in the north east of England. His role is to provide technical advice to growers over an area extending from Lincolnshire to Scotland. Prior to this, he was an agronomist with the company for 15 years and continues to provide agronomy advice to a number of growers producing combinable crops in the Scotch Corner area.

 

16 October 2017

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