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Role for ferric phosphate as season progresses

Mild, wet winters followed by warm, damp springs can mean only one thing – slugs. The potential for crop damage is undoubtedly high if wetter weather returns this autumn.

Mild, wet winters followed by warm, damp springs can mean only one thing – slugs. The potential for crop damage is undoubtedly high if wetter weather returns this autumn. An early metaldehyde treatment may be necessary on high risk fields to reduce breeding numbers and populations of slugs, believes agronomist Chris Martin, Technical Services Manager for Agrovista.

Identifying the fields most likely at risk from slug attack before the crop establishes is an important part of any slug control strategy, explains Mr Martin. “In some fields flag leaves have been nearly stripped so there are high numbers of slugs about.

Growers need to be aware that crops following cereals may be at higher risk than usual during establishment and early monitoring using traps in stubbles is a good way of highlighting where slugs are likely to be a problem. Where slug pressure is high, seed treatments can help initial emergence by protecting the seed from slug hollowing and it may be necessary to consider planting higher seed rates, depending on conditions and time of drilling,” he advises.

Good cultural control is the first line defence in keeping slug damage at a minimum. Achieving firm, fine seedbeds is vital to get the crop away quickly because it helps preserve soil moisture and gives good seed to soil contact for rapid emergence, says Mr Martin.

“Historically growers will know the cloddy areas in their fields, these tend to be around knolls and banks.  Get the soil in the best condition possible, consider double rolling difficult areas to try and consolidate the top 2 inches. The aim, for both oilseed and cereal crops, is to reach the 4 leaf stage as quickly as possible, by which time the crop is past the danger stage.”

With the imminent withdrawal of methiocarb, growers have just two actives remaining for slug control. Using metaldehyde strategically to protect water is the only way growers have to ultimately protect choice in the marketplace.

“An early application before drains are running is the best time to use metaldehyde to rapidly reduce slug numbers,” advises Mr Martin. “Thereafter I will switch to ferric phosphate pellets (Derrex), even if I have spare metaldehyde capacity (stewardship guidelines are no more than 210g/ha metaldehyde between Aug 1st and Dec 31st).”

Established populations of slugs can be difficult to control, especially where juveniles are present. “Juvenile numbers have been horrendous in the past couple of years because slugs have been breeding at a prolific rate. One of the strengths of Derrex over metaldehyde is that it does a better job of killing juvenile slugs,” says Mr Martin.

“Another advantage is that Derrex pellets last longer without losing their activity, especially when conditions are wet, so it is the better product to use going in to the winter. You can treat the whole field ‘hedge to hedge’, apply several treatments and have peace of mind in catchy weather conditions.”

In the five years since ferric phosphate pellets (Derrex and Sluxx) first came on to the market, grower confidence has increased year on year, especially since the extremely testing winter of 2012.

“Farmers using Derrex have now got used to not seeing dead slugs – they are seeing the crop recover and that gives them confidence,” explains Mr Martin. “Some of my growers won’t use anything else because it works and gives them the flexibility to respond to slug pressure without the environmental concerns.”

Helping growers understand when it the optimum time to use metaldehyde will help keep it on the market and preferable to growers being forced down a route with no product choice, believes Inez Cornell, Certis’ Arable Product Manager.

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