Don’t take risks with slugs in OSR

The main establishment phase of OSR is just around the corner, so slug control should be planned now.

It is well known that slugs don’t like hot, dry conditions, as their bodies are prone to drying out in the absence of moisture.

After a wet winter, a very dry spring followed for much of the UK and combined with more recent heatwaves will have had some negative impact on slug populations. 

However, on heavier, more moisture retentive soils that typically present a high degree of slug risk, populations won’t be wiped out completely.

Survival instincts

Instead, survival instincts will have led some slugs to retreat down the soil profile where conditions are more favourable, according to Harper Adams slug expert Keith Walters.

He says they can creep down cracks and crevices to find cool, moist conditions and are able to get some nutrition from organic matter present within the profile.

Even with this organic matter to feed on, the pest may travel up to the surface at night to feed, and if oilseed rape has been sown and germinated, it will provide an ideal meal.

“You need to think in 3D – not only what is happening at the surface, but also underneath with slugs moving up and down the profile.”

“Despite the year we’ve had, I would be inclined to not take the risk when planting oilseed rape. Get out there and check for slug activity with traps ahead of planting,” explains Keith.

He adds that during the critical germination and establishment phase, if soils are a little dry on the surface, seedlings can come under stress from the greater effort required to push roots down to moisture.

This can lead to slower growth at a more slug-vulnerable stage, so it makes it even more critical to ensure the crop is protected from attack.

“Where monitoring does reveal potentially damaging activity, it should certainly prompt the use of appropriate control measures to address the issue,” notes Keith.

Slug eggs

In Yorkshire, Association of Independent Crop Consultants (AICC) member Ben Boothman agrees that assuming the dry conditions will mean low slug pressure could lead growers down a path to unexpected plant losses.

Although not as abundant as last year, he is still finding slug eggs within the profile of heavier soils, so it would only take a couple of days’ rain to stimulate greater slug activity on land destined for OSR.

Following a good season for growers in the North, Ben says they will be encouraged to stick with the crop and maintain their current area.

His clients tend to drill as early as possible to get the crop up and away in warm conditions and before cabbage stem flea beetle migration and this will be aided by the early winter barley harvest.

He is an advocate of higher seed rates to negate pest pressure and establishment across his OSR area tends to be by direct drilling or via a seeding unit on low disturbance subsoilers to help retain moisture.

“I’m all for rolling after drilling, as it also helps moisture retention. It will consolidate the seedbed and reduce slug pressure as well,” he adds.

With so many risks during establishment of oilseed rape, Ben says an application of slug pellets soon after drilling is pencilled in on fields with heavier soils and a history of slug pressure.

“It gives plants the best chance of getting away. On lighter land, it might be possible to hold off, but we’ll see how things play out,” he explains.

Many of his farms stock up for the drilling campaign and tend to stick to one good quality brand, typically Sluxx HP.

“We’d sooner use a slightly lower dose of Sluxx HP, between 3.5–5kg/ha, than apply cheaper pellets.

“We’re monitoring crops regularly early on and if things turn wet and pressure increases, you can up the rate to 5–7kg/ha for follow up treatments,” he explains.

Baiting points

Certis Belchim’s Nathan Whitehouse says the firm developed a smaller version of the standard sized Sluxx HP ferric phosphate pellet, called Menorexx, for early OSR treatments.

“Growers look to apply the same weight of product, but it’s distributed over more baiting points. Looking at numbers, 7kg/ha dose of Menorexx provides 94 baiting points/m2, which is almost double that of Sluxx HP at the same rate,” he explains.

Nathan adds that because of the product’s smaller size and if conditions turn wetter during the critical establishment phase, more frequent applications of Menorexx may be needed, or a switch to Sluxx HP might be more suitable.

“Spreaders should be well maintained and calibrated correctly for the product being applied, as they do have different ballistic properties.

“We support spread widths of up to 24m for the smaller Menorexx, while Sluxx HP can go to 36m in ideal conditions. Growers can check what their applicator is capable of and find the correct settings using our online Calibration Wizard tool.”

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