Potato Review

www.potatoreview.com POTATO REVIEW MAY/JUNE 2022 47 SLUG CONTROL holistic view across the rotation and try to reduce populations of all pests, which helps reduce reliance on crop protection inputs. “We can then bring in interventions where absolutely necessary to ensure direct damage is reduced,” he adds. Mike Simmons, an Agrii agronomist based in Kent, looks after potato and horticultural crops across the county and has recently removed the radish component from cover crops on some clients’ farms. “The radish was doing the heavy lifting in terms of building the slug population and we thought we could do without it in the rotation,” he adds. Traping intelligence Mike reports mostly good seedbed conditions this spring for potato planting, but some of the earlier fields on more bodied soils did have some knobbly ridges early on and will need to be monitored. He sees bait trapping across the potato area as a positive thing, but only one part of a cross-rotation approach to slug control, helping to build up a picture of populations or hotspots for future years. During the season, results from baiting can be useful, but often looking at weather data and forecasts alongside soil type, crop development and irrigation scheduling will highlight where slug risk is likely to increase and help pre-empt where interventions are needed. “If we are expecting them, pellets need to go on before there is the possibility of any significant damage,” says Mike. Typically, when using pellets Mike will recommend application when conducive conditions are expected just ahead of canopy closure, then a top-up a few weeks later if conditions dictate. In irrigated crops – about half of his advised area – this is a given. Ferric flexibility “As we can no longer use metaldehyde, it is only ferric phosphate from this season onwards. I like the flexibility it provides, as pellets can be applied right up to the field boundary and gives peace of mind that we are doing right by water quality and the environment. “As a product choice I’m happy to recommend Sluxx HP, particularly in potatoes. It has the right balance of spreading well, the durability we need and a competitive price against other options,” he adds. Later in the season, he says many of his clients are harvesting “green tops”, so late applications to protect tubers ahead of harvest are not always necessary and with canopy penetration difficult, not always effective. However, in the proportion that are burnt off and left in the ground to set skin, conditions are monitored and a top up of slug pellets applied where a risk of tuber damage is apparent. Mike also reminds growers of the importance of correct application, with the ideal scenario that slug pellet applicators are serviced and tray tested ahead of the season to ensure they are working correctly. He adds that the applicator also needs to be set at the right height above the crop to ensure that the right spread pattern is achieved. Most machines need to be 1-1.5m above the canopy. “The least you should be doing is getting out the cab to check that pellets are reaching across the target spread width. “Consider the weather and irrigation plans, too. As pellets are usually spread at the same time as applying blight sprays, try and find a happy medium where neither will be adversely affected by conditions and do not apply just before irrigation water.” Field efficacy With metaldehyde finally out of the market after a protracted withdrawal, Nick says conversations with potato growers continue about the merits of ferric phosphate pellets to control slugs, with the active working in a different way. Slug mortality isn’t immediately evident after application like with metaldehyde, so the reference point for efficacy is the crop rather than dead slugs on the surface. He says manufacturer trials have supported its reliability in reducing slug damage in potatoes for some time and growers just need to go through a process of getting comfortable with ferric phosphate use in a crop situation. “Overall, we are happy with the results and recent changes to formulations of ferric phosphate pellets has certainly brought improvements in the field,” concludes Nick. ➜