With compromised ridge structure likely to be a consideration when planning slug control in potato crops this season, Farmers Guardian asks a leading agronomist for advice.
Poor soil conditions have featured across large areas of the country this season as a result of the exceptionally wet, late winter weather.
Subsequently, many potato growers are finding that crop ridge structure has been compromised and crops are likely to be at increased risk from slug damage as a consequence, where pressure is high.
This is according to Agrovista agronomist Neil Buchanan, who has been advising growers for 40 years, and oversees about 400 hectares of potato crops in east Shropshire and Staffordshire.
He says rather than achieving a fine mass of tilth, in many cases ridging and de-stoning cultivations this year have produced cloddy ridges which provide entry points for slugs.
In addition, dry weather since planting has meant an intensive start to the irrigation campaign, increasing the likelihood of slug pressure in crops.
Mr Buchanan says: “Too many clods formed during cultivations will mean the integrity of ridges will come into question as the season progresses.
“So it will be imperative to get slug pellets down in the crop to control the early surface feeders.
“They are the population which could cause damage to tubers later, creating marketing issues for crops destined for processing.”
Mr Buchanan has recommended the use of ferric phosphate-based slug pellets for some time, having ‘seen the writing on the wall for metaldehyde’.
Ferric phosphate has a better environmental profile, no buffer zone restrictions and zero harvest interval, he says.
“Slug pellet applications are nearly always combined with blight spraying and often follow shortly after irrigation, enhancing the need for good product persistence.
“Growers new to ferric products will notice some subtle changes from metaldehyde. No longer do we see the obvious carnage of dead or dying slugs, but efficacy is every bit as good, particularly against juveniles.
“Lack of pellet visibility can cause concern, but closer scrutiny proves these fears to be unfounded.”
Slug pellet application in potato crops occurs at specific times in the season and, following trapping operations to gauge pressure, Mr Buchanan says the first critical control period typically occurs in late June/early July, when the crop canopy meets across the row.
At this point, he recommends an application of Ferrimax Pro, which achieved registration for use in potatoes for the 2020 season, at 5kg/ha.
He says: “This is when surface feeding slugs can be found on the ridges, particularly in irrigated crops where a micro-climate can be formed under the canopy.
“The second period, some four to six weeks later, is when tubers start to bulk and slugs left uncontrolled will go down through the cracks in the ridges and begin to graze on tubers.”
With a 7kg/ha rate applied at tuber bulking, a final (5kg/ha) application can also be made at crop defoliation, says Mr Buchanan, adding he will rarely carry out more than these three specific applications.
“Haulm removal is a key time to monitor for slugs, as the crop continues to skin set. And if lifting is delayed, as was the case last autumn, potatoes are prone to attack and growers run the risk of late damage.
“Controlling slugs in potatoes is all about protecting market quality, with the best products available.”