With ‘slug season’ rapidly approaching – and likely to present a significant threat this autumn thanks to recent wet weather which has boosted slug populations – we talk to Olly Pemberton, Velcourt’s Farm Manager for RJ Hussey and Son at Weir Farm on the Marlborough Downs, and John Gould of Castle Farm, Fotheringhay in Northamptonshire to find out how they intend to control slugs without metaldehyde.
In a typical year, how severely do slugs affect the viability of your autumn sown crops?
Olly: The degree of damage very much depends on the previous crop and prevailing weather conditions. This year the potential for crop damage could be quite high based on the fact that the wet weather we had in late spring coincided with the slug breeding season which means populations will be high. We’ve also seen some significant rainfall during the latter stages of spring and into the summer months which will have helped the slug population to prosper.
Olly Pemberton, Velcourt Farm Manager
John: Slug damage is certainly a concern for us, but I’d classify the amount of damage caused as moderate as opposed to severe. That said, this autumn’s anticipated high populations could cause some real damage if we don’t get our control strategy just right.
In a typical year, what percentage of your crops will you treat with a molluscicide, and how often do you apply pellets?
Olly: Any wheat being grown after winter oilseed rape will generally receive two applications of slug pellets. For second wheats and other cereals we’re not quite as vigorous, with pellets only going on if and when grazing is seen. We always apply slug pellets on winter oilseed rape crops, which means we’re routinely treating 50% of our arable acreage and another 25% treated as required.
John: Probably 40% of our crops are affected by slugs, with 60% of our wheat area, 20% of winter barley and 80% of our oilseed rape at risk in any given year.
Which molluscicide active ingredients have you used in the past?
Olly: We’ve historically used metaldehyde-based slug pellets such as ADAMA’s Gusto 3 and Tempt. Obviously, those products are no longer available, so we’ve switched to Gusto IRON instead.
John: We’ve used a range of products over the years, with metaldehyde our preferred choice for the bulk of our crops. Last year we used Gusto 3 to good effect so it’s a shame to see it go this year.
What do you look for when choosing slug pellets?
Olly: As far as I can tell, there’s very little, if any, difference in efficacy between metaldehyde and ferric phosphate so it isn’t too big a deal that the former is no longer available. What’s more important are pellet consistency, spreading accuracy and baiting point density, all of which are absolutely vital to ensuring good ingestion rates. Input costs are also important, with the price per hectare more important than price per kilo of pellets. Unfortunately, ferric pellets seem to be a little more expensive than metaldehyde products used to be. That said, we at Velcourt have voluntarily used ferric phosphate in the past to ensure we maintain good environmental and water stewardship standards
John: I agree with Olly in that the key factors for me are spreading accuracy and pellet longevity in wet conditions. Pellet palatability and active ingredient efficacy are also crucial because it makes no sense to apply pellets if they aren’t then going to be ingested and do what they’re supposed to do. Baiting point density is also important for the same reason.
Why have you chosen to use Gusto IRON this year?
Olly: The withdrawal of metaldehyde means we have had to increase the amount of ferric used on farm. Fortunately, we were already using ferric phosphate on our headlands, so it has been fairly simple for us to shift everything across to Gusto IRON.
John: Our agronomist recommended Gusto IRON to us so we went with his advice, predominantly because we’d had such good results from the year when we applied Gusto 3.
What baiting point density do you typically aim for when applying slug pellets?
Olly: 45-50 pellets per m2 gives us adequate coverage.
John: About 25 pellets per m2 seems to give us the desired effect on our land.
How do you apply slug pellets and to what working width?
Olly: I try to avoid placing slug pellets underground with the seed as the majority of products aren’t approved to be used in this way, so we use a quad-mounted spinner to apply directly to the soil surface. Our setup allows us to spread accurately to 12 metres.
John: We use an Opico Variocast applicator to apply pellets to 12 metres.
How do you assess the slug threat in your crops?
Olly: Nothing beats getting out there and walking the crops to see what they need, so we use visual checks to look for signs of grazing and also use traps and look under rocks and stones to determine if and when slugs are active.
John: We base our initial assessment on the amount of visual damage seen in-season and the number slugs trapped in our bait points, but we also consider historical slug populations and damage to form part of our risk assessment.
When do you apply slug pellets?
Olly: My preference is to apply at pre-emergence (assuming threshold numbers have been reached) but we’ll also apply through the season as and when additional protection is needed.
John: We’ll start applying pellets as soon as the first signs of damage appear, with historical damage also being taken into consideration to ensure we’re as proactive as possible.