Growers shouldn't worry about the loss of metaldehyde from the slug control armoury, says Herefordshire-based agronomist Andrew Goodinson of Hutchinsons. In his view, good quality ferric phosphate alternatives are every bit as effective and also provide a better environmental footprint.
Andrew's been recommending ferric phosphate for over five years and he's gradually phasing metaldehyde out. "Metaldehyde has always been a cost-effective slug control option where applied properly, but I was looking for safer alternatives with a better environmental profile. Ferric phosphate has proven to be a perfect replacement, matching metaldehyde for efficacy and cost effectiveness" he comments. Targeted slug control is a good insurance against oilseed rape caused by poor establishment, he says.
"Ultimately, it's about protecting plants that have been drilled into poor seedbed conditions and are at high risk from slug grazing, including crops that are showing flea beetle damage. "Last autumn we'd still have had a challenge to establish OSR, even without the flea beetle issue, because of the dry cloddy seedbeds. Seedbed conditions are more important than drilling date. If conditions aren't right for planting oilseed rape then don't" he says.
Andrew points to a number of Hutchinson's foundation agronomists who have carried out dissertations on slug control. Summarising the findings, he highlights that while the level of control was the same as with metaldehyde, the habit of the slugs after ingesting each product was very different. In the case of ferric phosphate, they stopped eating immediately and retreated underground where they died within a few days.
"We've found crops recover more quickly where ferric phosphate has been applied, which is probably to do with the fact that the slugs in crops treated with metaldehyde continue to feed for some time before dying" he explains.
"Application timing is also critical, with adult slugs being the target rather than juveniles, especially in cereals. So regular monitoring of traps is essential."
In terms of pellet quality, he recommends the wet process ferric pellets on the market, which are good quality and spread well, giving even coverage of baiting points.
"Bait quality is critical to the level of control. Poor quality pellets can't be applied accurately over wide distances (max 15m), so the weight and shape of each pellet has to be consistent to ensure even application and accuracy is maintained across the full working width."
Andrew stresses good application is important to ensure the correct number of baiting points/m2. Consistent pellet size helps achieve this and with larger pellets, they remain persistent for longer and its larger surface area to volume ratio helps concentrate the active ingredient.