Slugs have been a major headache for Yorkshire grower Graham Potter as he transitioned from a plough-based crop establishment system to direct drilling. But with proactive implementation of integrated slug control methods and a sprinkling of new technology, he has turned the tide against the damaging pest across his 200ha arable farm near Thirsk.
Soil health has been a major focus for Mr Potter in recent years and part of his strategy to improve soil organic matter has been reduced tillage and the introduction cover crops in to the rotation. In 2013, the previous plough-press-drill system was ditched in favour of the tine-based strip-drill setup from machinery manufacturer Claydon.
However, with the slug’s habitat no longer disturbed by deep inversion tillage, crop damage increased and resulted in a re-assessment of slug control strategy on the farm.
“The slugs got worse and worse when we started direct drilling, but as my understanding of the slug itself has improved things have slowly gotten better,” explains Mr Potter.
This increased knowledge of slug ecology and behaviour has seen a number of techniques implemented to try and eliminate the problem without chemical intervention, which is only used as a last resort.
The first is the use of a 7.6m Claydon stubble rake, which is deployed a number of times between harvest and the establishment of the following crop, particularly after oilseed rape when slug pressure tends to be at its highest.This helps spread crop residue evenly across the soil surface, minimising any habitat favourable to slugs. The rake also inflicts physical damage and exposes slugs and slug eggs to the elements or natural predators.
“It’s much more effective when hot and dry and we’ll take advantage of any hot weather to rake once harvest is over.
“However, we don’t get too many hot days in Yorkshire, so we also rake at night when slugs are active on the soil surface to get a better effect when conditions are cool and damp.”
Rolling and drill depth
With each tine coulter in the strip-drill system loosening a narrow band of soil, it can provide an easy route for slugs to move down rows and feed on seed. Recognising the importance of seed-bed consolidation, Mr Potter has now taken to double rolling after drilling where slug risk is high, firstly in the same direction as the drill, then a second pass at 90deg to close up the slot.
This helps with seed-to-soil contact for rapid establishment and reduces the ability of the slug to move within the seeding zone. Trials run by Mr Potter comparing no roll, one roll and two rolls showed much improved control from two passes.
“Where we know there are slug problems, we also slow the speed down from 8kph to about 5kph to improve consolidation,” he adds.
Mr Potter also uses drilling depth in high risk areas to hinder the pest’s ability to get to seed and cause damage. Typically, wheat would be drilled about 1in deep, but depth is increased to 1.5-2in in slug prone areas or in wet seasons.
Mr Potter has been an early adopter of precision farming technology and one of the tools he has used is an electroconductivity (EC) scanner to produce management zones based on soil types across his farm. These vary from heavy clay to blow away sands and once zoned, it gave him the chance to marry up the EC maps with observed slug risk.
This has been underlined more recently by drone images taken when damage is seen in the crop, allowing thin, slug-grazed patches to be mapped and saved in record keeping software programme Gatekeeper for future reference. Most observers would assume that the heaviest soils would present the highest slug risk, but Mr Potter’s work has uncovered that his medium loams suffer the most crop damage. Using EC maps and variable rate seeding technology, he has been varying seed rates based on soil type for some time. However, he is now layering slug risk data over the top of seeding maps and adds an extra 20-30kg/ha of seed where slug risk is high.
“It helps to negate the losses caused by hollowing and has made a big difference to plant populations since we’ve been doing it,” he adds.
Variable pellet application
In addition to upping seed rates in hotspots, Mr Potter is also combining EC, slug risk and yield data to produce variable rate slug pellet application maps. This enables him to apply a higher rate of ferric phosphate pellets in problem areas on medium soils, and less where risk is low, without exceeding the overall maximum individual dose on the product label.
“The heavy land might only get 4kg/ha, but where we know it’s bad, we will go up to 7-8kg/ha,” notes Mr Potter.
Ferric phosphate switch causes no concern
The ban on metaldehyde use in outdoor crops in June 2020 is causing Mr Potter no worries, having moved away from the outgoing active in autumn 2017.Mr Potter is a monitor farm for Yorkshire Water and part of the Sustainable Landscapes project, which has aimed to reduce the amount of metaldehyde polluting raw water supplies across the region.
As a result, he has been proactive in looking for non-chemical solutions to slug control and switched to alternative molluscicide ferric phosphate – a naturally-occurring substance with no buffer zone requirements – in 2017.
“Control has been fine with the ferric phosphate. The only difference is that you don’t see dead slugs like you do with metaldehyde, as they go under the soil surface to die.
“It is just a case of going out and checking the crop for damage or if the pellets have been eaten to know if you’ve done any good,” explains Mr Potter.
He adds that he has done some trials comparing market-leading ferric phosphate product Sluxx HP with rival Ironmax Pro, which claims to have an attractant that makes the bait more appealing to slugs, but he saw no evidence of improved control for the extra cost.
Graham Potter’s slug control tips
For more information on slugs and slug management visit the Slug Force Hub.