Potato Review

26 POTATO REVIEW MAY/JUNE 2020 MOLLUSCICIDES Jon pointed out that Maris Piper, still the most widely grown in the UK, is particularly susceptible to slug damage, which can also be commonly confused with wireworm damage. Wireworms are the larva stage of the click beetle. e beetles themselves do very little damage to potatoes but the larva do, and the combined damage of the two pests can push the delivery into a ‘fail’ category when the load is checked at the factory QC intake. “Ferric phosphate is an e ective alternative to metaldehyde for reduction of slug damage in potatoes,” Jon said. “Currently ferric phosphate and metaldehyde can still be used sequentially in programs with no loss in e cacy. e key timings for molluscicides application in potatoes are just before the crop canopy meets across the rows up to early tuber bulking but protection should be maintained right through to burn down of the crop.” While growers sometimes put slug pellets on at planting, agronomists have claimed this is overzealous, and the most e ective use is to the canopy. “You can apply up to four times, with a 7 Kg/Ha application but the important thing is persistence of that pellet,” Jon said. e dependability of ferric phosphate is nothing new, he added, referring to independent AHDB trials carried out at Carrington, Lincolnshire, and in Edinburgh, in 2015/16, which had shown at the time that three treatments of ferric phosphate applied to tubers with slug damage were giving as good, if not better, results as all other combinations, including metaldehyde. De Sangosse’s newly-launched slug pellet for potatoes, Fe-Lyn, contains 24.2g/kg ferric phosphate and we were shown how it performed in the lab and the eld. In France, where the research centre is based, the Government has dictated that by 2025 there must be a 50% reduction in pesticide use. e ferric phosphate slug pellets are classed as a biological control method, and De Sangosse has now become a global leader in the supply of slug pellets, we were told by Communication and International A airs Manager Christophe Zugaj “Our strategy now is clearly on bio solutions,” he said. Bait technology and environmental pressure De SangosseCommercialManager, Phil Carpenter, stressed the importance of bait technology as a solution to draw in the slugs and ensure they properly ingest the active ingredient. “It is all verywell to have your slug pellets on the ground but youdo need something to attract the slugs tomake sure it is going to impact in the right place,” he said, pointing out that high-quality baits help the plant to achieve e cacy. “Baits are the only pesticides used in agriculture that require being found by the pest and ingested in su cient quantity to cause death,” he said. “ e bait itself is as important as the active ingredient.” In our tour of theDe Sangosse factory and R&Dcentre, wewere able to see evidence of this, although the recipes for the slugs’ deadly dish is kept highly con dential. JennaRoss, InnovationHubLead for AgriCentre, CropHealth andProtection (CHAP), who also attended the tour, works extensively in slug research. She con rmed there is a natural death of slugs and, with stomachpoisoning, it takes thema fewdays to die after consuming the pellets. In the ferric phosphate productswewere shown on our De Sangosse visit, less than 5%of the product ismade up of the active ingredient. e remaining 95%to 99% is a combination of rawmaterial (wheat/durumwheat) and recipe, essentially to provide attractiveness, palatability, spread-ability and ability towithstand environmental pressure, essentially high rainfall. Leaching canbe a challengewith slug pellets and at the R&Dcentre, wewere shown rst-handhow De Sangosse has devised a recipe that enables the products tomaintain their pellet form. Agronomists advise that slug pellets should be considered in the spring, months in advance of planting, with one application of pellets before the canopymeets across the rows. ey also advise against excess irrigation because of pellet leaching, but growers can still fall into this trap, particularly in dry periods whenwater is so essential to potato development, said Phil. is is why there had been such a focus from the technicians in Agen on creating a pellet form that canwithstand excess water, be it through rainfall or over-zealous irrigation. Agrii potato specialist and agronomist, Ben Naylor, whowas interviewed in the last issue of PotatoReview following the launch of the Fe- Lynpotato label, said around 70%of his growers had already changed to ferric phosphate andhe believed the rest would soon followsuit. He is responsible for agronomic advice across 2,000 acres of potatoes grown inEast Shropshire, Sta ordshire andWarwickshire. Growers are urged to regularly assess slug populations on landused in crop rotations. e De Sangosse teamsaid this is essential if you are going to allowenough time to take e ective control measures before the crop becomeswell established andmore susceptible to slug attacks. “ e timings for ferric phosphate applicationwill be identical tometaldehyde and the need for their usewill be drivenby previous eldpressure, variety and soil conditions,” saidBen. Control tips: Moistureand temperature: Slugs depend onmoisture for activity, survival and reproduction. e optimumtemperature of the eld slug is 17 o Cbut it will remain active even close to freezing. Soil Type: Heavy soilswithhigh clay or silt content provide goodhabitats for slugs as the seedbeds on these tend to be open and cloddy, allowing easy movement for the slugs. Previous cropping: Slug damage is greater after leafy crops such as oilseed rape than after potato crops. Cropresidues andotherorganicmatter: Crop residues incorporated into soil or applications ofmanure, especially in the autumn, provide slugswith a food source and shelter. Cultivationandseedbedpreparation: Non-inversion tillage increases the risk of damage by slugs. Ploughing is a goodway of reducing slug populations. e grey eld slug (Deroceras reticulatum) is the most widespread and troublesome species. It is usually light grey or brown, grows up to 5cm in length and produces milky white mucus. Populations tend to have a mixed age structure, so damage occurs whenever conditions are favourable for activity. It continues to be active indamp weather and evenwhen temperatures are close to freezing. Breedingisgenerally atapeakinApril/Mayand September/ October. In favourable conditions, it will breed throughout the year. In optimum conditions, it can start to lay eggs within 16 weeks of hatching. Phil Carpenter Jon Williams