Potato growers must use up stocks of methiocarb slug pellets before September and are advised to try alternatives ahead of its absence next year.
The active, contained in products such as Bayer’s Draza Forte and Decoy Wetex, has a good track record for controlling slugs in spuds and accounted for about 50% of the potato slug control market until this season.
The EU voted to ban the chemical for use as a slug killer in January 2014 due to the risk of harm to grain-eating farmland birds.
Agrochemical distributors had until last September to sell methiocarb-based pellets and many growers attempted to secure supplies for this growing season.
John Keer, potato expert at Richard Austin Agriculture, says growers who have stocks of methiocarb pellets will have the advantage of an extra weapon against the pest.
However, he believes even where growers have supplies, they should start looking at alternatives to get a feel for how they work on their farm.
“With methiocarb lost and metaldehyde under threat growers need to be prepared, particularly on heavier land or if you are growing slug-susceptible varieties such as Maris Piper,” he adds.
Dr Keer will be carrying out small plot trials this season, including available treatments of metaldehyde and ferric phosphate-based pellets and the biological control, Nemaslug.
Where this is too time-consuming for growers to set up, comparing products in adjacent tramlines or field-by-field will also provide valuable information for future control strategies without methiocarb.
“Don’t discount Nemaslug, as it can give effective control if used correctly, but soil moisture is crucial as water helps the parasitic nematodes move though the soil,” adds Dr Keer.
Potato packers and processors have various protocols in place for growers, including a list of pesticides that may or may not be applied to the crop.
With methiocarb now banned, Prime Agriculture agronomist Colin Smith – who works across Cambridgeshire and Norfolk – advises growers to check with the end user if they will accept crops treated with the active ingredient.
“Although legally it can be used until 31 August, protocols may have changed to take a dim view of using methiocarb because of its less favourable environmental profile.
“It’s a good idea to ask the question and avoid any potatoes being rejected at delivery time later in the year,” he says.
Slugs cause direct feeding damage to tubers and can take a crop from the best pre-pack supermarket grade to stock feed if allowed to thrive.
Although it is too early to predict slug risk for the spring, Dr Keer points that cultural controls should be the first thought when considering a strategy as chemical control options dwindle.
“When planting high-risk varieties such as Piper on heavier land, aim to produce a fine tilth for planting or reconsider field selection altogether and choose a lighter land site,” adds Dr Keer.
Mr Smith advises setting out slug traps to assess numbers in stubbles ahead of planting in February and March and apply pellets where slug activity is found.
With metaldehyde under pressure from regulators for being found in raw water supplies, he leans towards using ferric phosphate pellets for any pre-planting applications.
“Grey field slugs come up to the surface to breed in the spring, so it provides a good chance to reduce numbers ahead of the crop going in the ground,” he adds.
Little and often
Post-establishment, both Mr Smith and Dr Keer prefer a little-and-often approach, applying low doses of pellets using a sprayer-mounted applicator with every other blight fungicide spray from just before canopy closure.
Growers are not limited by the number of applications, but are restricted by quantity of active ingredient used during the season, so alternating products is crucial to stay within label guidelines.
Mr Smith believes using frequent low-dose applications of high-quality pellets is preferable as it keeps baiting points present throughout the high-risk period as tubers develop.
“You are going through the crop with blight sprays anyway, so it isn’t costing extra to apply the pellets,” he adds.