Potato growers pondering their slug control optionsthis season following the withdrawal of methiocarb should not be disheartened,says a respected independent agronomist.
For the past few seasons potato agronomist NeilPratt of Techniculture has been utilising several different types of pellet toachieve effective control while observing all relevant environmentalrestrictions.
For many potato growers methiocarb was regarded asthe pellet most suited to slug control, but in practice growers often usedseveral different types depending on the situation.
Over the past few years we have favoured TDS asour choice of metaldehyde pellet because it features the same attributes foundin methiocarb-based pellets. It means there is no need to revise applicationtimings, but there will be instances where we have to respect a watercourse andin such circumstances I advise switching to ferric phosphate-based pellets,says Neil Pratt.
His standard course of action is to apply 5kg/ha ofTDS, a metaldehyde pellet, to provide 30 baiting points/sq M.
Research has shown that there is a trade-offbetween baiting points and pellet size with 30 pellets/sq M found to be aboutthe optimum for a range of crops and conditions.
To those pondering which pellet will offer thelevel 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 its important to match pelletchoice to situation. Durability and ballistic performance are theprincipal considerations, these attributes determine how consistently thepellet spreads and how long it persists in the field.
The pellet also needs to be highly palatableotherwise the pest can become bait shy. In practice this means using a pelletthat is produced using durum wheat. Fortunately, this also supports our needsfor durable pellets as the flour is often finer and leads to a pellet with atighter surface texture which means they can withstand weather pressure forlonger.
Beyond pellet choice, good control is largely aboutgood field management. Application timing is important and when there is theopportunity to control slugs in stubbles in the late summer early autumn headvises growers exploit it. Unfortunately, this is not always possible whichraises the importance of good spring control. Application across the ridgespresents a further challenge and raises the importance of good ballistics if agood spread is to be achieved.
Ensuring the first application is on before canopycomplete is fundamental to achieving good control at this time. Once thecanopy meets between the rows it is difficult to reach soil below and this isthe last opportunity to target the slugs before tuber initiation. If you missthis opportunity, then control becomes significantly harder to achieve and isone reason why I treat in the autumn whenever possible, he says.
Although some varieties are known to be morevulnerable to slug attack Maris Piper, Marfona and Saxon are examples wherever oilseed rape features in the rotation slugs will be an issue meaningthere is rarely an opportunity to save on pellets.
Similarly, Mr Pratt is wary of relying oncultivations alone to control populations suggesting it is not a tactic thatcan be relied on to achieve a meaningful level of control.
While early season presents the best opportunity totackle slugs, there are instances where a follow-up application is required,but Mr Pratt says it should not be considered routine, especially if liftingearly for seed or salad purposes.
The need for a follow up application later in theseason is largely determined by intended lifting date and the success ofearlier applications.
One pass is often enough, especially if lifting inAugust, but where lifting is delayed until late September or into October, itis prudent to first carry out some test digs once the soil surface becomesvisible to establish pressure.
If ridges have become cracked it can also makeaccess easy for slugs and so where this occurs it is often worthwhile making asecond application, he says.