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A robust alternative

As available slug control options narrow and with the slug pressure forecast to be reminiscent of 2012, it is vital to plan control programmes for the season ahead.

As available slug control options narrow and with the slug pressure forecast to be reminiscent of 2012, it is vital to plan control programmes for the season ahead.


On the back of two successive high slug pressure autumns, the periodic wet spells that characterised much of this spring and summer have provided fantastic conditions for slug breeding and survival.


After a mild winter of 2013/14, experts subsequently reported a lot of flag leaf shredding in wheat crops early this summer, and after a period of dry conditions, the resumption of the wet weather has seen slugs return in force, just in time for the main establishment season.


Preventative measures, after an early harvest, will be a key component of any strategy.


Field history
Many growers will know the historically heavy soils and cloddy areas in their fields and where to concentrate efforts. They tend to be around knolls and banks and are the most important areas to get into the best condition possible, which many require double rolling in order to consolidate the top two inches of soil.


Well consolidated seed beds will allow young establishing plants to get away and pass the critical stage as quickly as possible; leaving seedlings less vulnerable to on-going slug damage.


For oilseed rape the critical point crops need to reach is the four true leaf stage. Up until this point serious damage can occur as, unlike cereals, the growing point is above ground.  Cereals are most vulnerable to grain hollowing from slugs up to growth stage 14, but will remain under pressure up until growth stage 21.


Yet, in many areas, wet weather will inevitably bring slug problems, so it’s important to be aware of the high risk field areas, especially during the crops’ most vulnerable period.


In light of the restrictions placed on metaldehyde and with the loss of methiocarb, that – from this month – becomes unavailable to purchase; ferric phosphate pellets are a genuinely efficacious alternative for growers.
Growing confidence.


Confidence in the relative newcomer treatment, marketed as Sluxx and Derrex is growing, and with good reason.


“The treatments deliver desperately needed industry solutions where pellet efficacy and strong environmental credentials are central to sustaining the pellet armoury,” notes Certis’ Technical Officer, Nigel Riches.


He outlines that Sluxx is a wet process, pasta based formulation, whilst Derrex is a high compression pellet, with both expected to feature prominently in 2014 treatment programmes. “They deliver high quality, durable pellets that also provide reliable and flexible control. They also facilitate a good level of baiting points, which is going to be key to stopping slugs feasting on seedlings this autumn.”


He adds that there are zero buffer zones when applying either of these formulations, making them attractive choices that can provide hedge to hedge protection.


Whilst fully replicated trials have shown that ferric phosphate will deliver on a par with metaldehyde; growers are also gaining anecdotal evidence.


For example, a producer based in East Anglia conducted his own non-scientific field trial to compare ferric phosphate and metaldehyde. Four high quality metaldehyde treatments were compared with a plot that received two metaldehyde and two Sluxx applications. The result was that slugs stopped grazing across both sides of the field; control and the level of crop protection was comparable.


Testimony to the pellets’ long lasting credentials under wet conditions has also been confirmed, as has their performance against juvenile slugs, which have been a horrendous problem in the past couple of years when the breeding rate has been so high. HGCA have reported that weight for weight, smaller slugs destroy more seeds than larger slugs, so control of juvenile slugs is vital in maintaining crop protection.


“With five years’ experience under our belts with ferric phosphate use in the market, since Sluxx was first registered, growers can be confident to switch where they haven’t tried it before,” confirms Nigel.
“Ferric phosphate proved itself in the horrendous slug season of 2012 and there was no better season to test the mettle of a slug pellet.”


Differences
Nigel maintains that while there are differences in the slug response to ferric phosphate pellets, compared to metaldehyde, they have no bearing on the control levels delivered.


“You won’t see the slime trails and dead slugs on the surface that are a hallmark of treatment with metaldehyde. But, what you do see is a lack of crop damage which is not so immediately visual, so a fundamental change in thinking and expectation is required due to the different mode of action.”


He explains that when a slug has eaten a Sluxx or Derrex pellet, it is soon unable to feed, which is why crop damage stops following the ingestion of a pellet. “As the pellet moves further along the slug’s digestive system the iron within the pellet displaces calcium in the cell walls of the gut.


“The digestive system disintegrates as it becomes poisoned, leading to slug death. Affected slugs move below ground to areas of moisture and low light which is why they’re not easily seen after treatment.


“Farmers using Sluxx or Derrex have now got used to not seeing dead slugs – they are seeing the crop recover and that gives them confidence.”

Metaldehyde
Nigel Riches adds that whilst Sluxx and Derrex are Certis’ flagship pellets, the company also sells a range of metaldehyde formulations and is a member company of the Metaldehyde Stewardship Group (MSG).


“Metaldehyde still has an important role to play in slug control,” he maintains.
“We need to do everything we can to respect the regulatory requirements for the levels of pesticide in water whilst also keeping metaldehyde available,” he says, noting the support shown by the water industry, where a balanced approach is being advocated in order to maintain a future for metaldehyde as part of the control armoury.


The stewardship guidelines advocate no more than 210g/ha metaldehyde between 1 August and 31 December and state that metaldehyde should not be used when heavy rain is forecast or where drains are flowing.


Understanding when is the optimum time to use metaldehyde will help keep it on the market and is preferable to growers being forced down a route where there is no product choice.


Meanwhile, ferric phosphate has no application restrictions, whilst boasting a strong environmental profile which enables slug pellet coverage to be achieved, without leading to detections in watercourses.


“This is an important consideration, particularly as drains start to flow. The flexibility to treat the whole field ‘hedge to hedge’ is very appealing,” says Nigel.


“Both metaldehyde and ferric phosphate are good slug pellets,” he adds. “Ferric phosphate is a huge part of the tool box growers have to keep metaldehyde out of water, and maintain pellet choice.”


Given the strong environmental profile, ferric phosphate formulations are suited for applications to crops situated in vulnerable water catchment areas, on fields directly adjacent to watercourses, and for treating headlands, as well as to fields when they are at, or beyond, full water holding capacity. There are also benefits on multi-treatment crops such as potatoes, where a following cereal crop imposes calendar year dose rate limitations for metaldehyde.