Extreme slug pressure and continuing wet conditions means maintaining metaldehyde stewardship standards are vital to ensure crops are protected without adversely affecting raw water supplies, says Dr Paul Fogg speaking on behalf of the Metaldehyde Stewardship Group.
“A delayed harvest and consequently later than normal drilling means crops have been slower to get away this autumn,” explains Dr Fogg. “Slow growing crops and wet soil conditions means they are vulnerable to slug damage for longer, so growers are facing a very difficult task this season.”
Record rainfall during April and May coincided with the main slug breeding season, providing ideal conditions. The weather has remained favourable for slug survival and continued breeding ever since, resulting in very high populations of both adult slugs and juveniles.
Agrii agronomist David Wild, describing the situation in Yorkshire and North Lincolnshire, says “The slug problem is major and the big surprise to me is the amount of juvenile slugs (some no bigger than a hat pin) that I am still finding.
“Where Deter has been used as an insecticide seed dressing on cereals, it appears to be doing a good job in protecting the seed from hollowing, but as the crops emerge they are susceptible to leaf grazing and stripping and this, in many cases, requires treatment.”
OSR crops have fared worst of all. “Many (surviving) crops now are starting to grow away from slug damage, but crops have been decimated and in many cases totally wiped out within seven days – even with pellet applications.
“Land conditions are not good, with crops being power harrowed in, and the seedbeds left unrolled and unconsolidated. Some land may have to be left unplanted this autumn. The open seedbeds create problems for both herbicide applications and slug control,” adds Mr Wild.
So what are the main things growers should bear in mind?
“Achieving good slug control and keeping crop damage to an acceptable level, while using the minimum amount of active ingredient is what growers should be aiming to achieve,” advises Dr Fogg.
“When field drains are flowing there is the most significant risk of metaldehyde losses into surface waters,” warns Dr Fogg. “The best practice guidelines state that metaldehyde should not be applied.
“Growers should be aware that there are metaldehyde peaks being reported in water catchment studies in some regions, which appear to coincide with peaks in rainfall, though it is too early to get a true picture of how raw water supplies will be affected at the point of abstraction.”
With repeated applications of slug pellets being necessary where crops are at a high risk of damage, judicial use of metaldehyde is being urged to keep within the stewardship guidelines of no more than 210g metaldehyde / ha in the period 1st August to 31 December.
According the MSG hotline (0845 177 0117), many growers have been calling to ask whether the 210g metaldehyde / ha is a statutory requirement or an advisory rate. “The 210 g/ha rate is advisory though, given the pressure this season, growers should be considering the advice as statutory if they want to keep metaldehyde in the armoury,” clarifies Dr Fogg.
This autumn is proving to be a real test of the stewardship measures, with the highest slug pressure since metaldehyde exceedances in raw water supplies were first noted in 2008.
“We already know that slug pressure is extremely high this season and many soils have reached field capacity. It remains to be seen how the MSG reduction in both the application rate and level of active substance in pellets will translate to the levels ultimately being detected at the point of water abstraction and the duration of any metaldehyde peaks that do occur.
“While the MSG fully appreciate the pressure some crops are coming under and the need to apply slug pellets, it is important to keep stewardship in mind so that the measures can be properly assessed and then adjusted if necessary to safeguard the use of metaldehyde in the future and protect water,” concludes Dr Fogg.