Potato growers pondering their slug control options this season following the withdrawal of methiocarb should not be disheartened, says a respected independent agronomist.
For the past few seasons potato agronomist Neil Pratt of Techniculture has been utilising several different types of pellet to achieve effective control while observing all relevant environmental restrictions.
For many potato growers methiocarb was regarded as the pellet most suited to slug control, but in practice growers often used several different types depending on the situation.
“Over the past few years we have favoured TDS as our choice of metaldehyde pellet because it features the same attributes found in methiocarb-based pellets. It means there is no need to revise application timings, but there will be instances where we have to respect a watercourse and in such circumstances I advise switching to ferric phosphate-based pellets,” says Neil Pratt.
His standard course of action is to apply 5kg/ha of TDS, a metaldehyde pellet, to provide 30 baiting points/sq M.
“Research has shown that there is a trade-off between baiting points and pellet size with 30 pellets/sq M found to be about the optimum for a range of crops and conditions.”
To those pondering which pellet will offer the level of performance they desire, Mr Pratt offers some simple advice.
“Growers need to look at what they are buying. There is notable differences between pellets and it’s important to match pellet choice to situation. Durability and ballistic performance are the principal considerations, these attributes determine how consistently the pellet spreads and how long it persists in the field.
“The pellet also needs to be highly palatable otherwise the pest can become bait shy. In practice this means using a pellet that is produced using durum wheat. Fortunately, this also supports our needs for durable pellets as the flour is often finer and leads to a pellet with a tighter surface texture which means they can withstand weather pressure for longer.”
Beyond pellet choice, good control is largely about good field management. Application timing is important and when there is the opportunity to control slugs in stubbles in the late summer early autumn he advises growers exploit it. Unfortunately, this is not always possible which raises the importance of good spring control. Application across the ridges presents a further challenge and raises the importance of good ballistics if a good spread is to be achieved.
“Ensuring the first application is on before canopy complete is fundamental to achieving good control at this time. Once the canopy meets between the rows it is difficult to reach soil below and this is the last opportunity to target the slugs before tuber initiation. If you miss this opportunity, then control becomes significantly harder to achieve and is one reason why I treat in the autumn whenever possible,” he says.
Although some varieties are known to be more vulnerable to slug attack – Maris Piper, Marfona and Saxon are examples – wherever oilseed rape features in the rotation slugs will be an issue meaning there is rarely an opportunity to save on pellets.
Similarly, Mr Pratt is wary of relying on cultivations alone to control populations suggesting it is “not a tactic that can be relied on to achieve a meaningful level of control”.
While early season presents the best opportunity to tackle slugs, there are instances where a follow-up application is required, but Mr Pratt says it should not be considered routine, especially if lifting early for seed or salad purposes.
“The need for a follow up application later in the season is largely determined by intended lifting date and the success of earlier applications.
“One pass is often enough, especially if lifting in August, but where lifting is delayed until late September or into October, it is prudent to first carry out some test digs once the soil surface becomes visible to establish pressure.
“If ridges have become cracked it can also make access easy for slugs and so where this occurs it is often worthwhile making a second application,” he says.