Continued dry conditions in many parts of the UK may have helped to keep a lid on early slug pressure, but oilseed rape growers should be ready to act swiftly should conditions turn unsettled.

Around the country, agronomists report wide variations in establishment, with forward crops at six true leaves but others near to one true leaf. Serious damage can occur up to the four true-leaf stage.

 East Yorkshire-based AICC agronomist, Andrew Beeney reports a total of four inches of rain in the last two weeks of August across the region.

 Any oilseed rape sown just prior to the rain, or between the showers, had plenty of moisture to establish well.

 “However, despite that rain, soils remain pretty dry at depth, and some later-sown crops were only just at the cotyledon stage by the third week in September.

 “Those crops could remain susceptible to slugs, if activity increases with wetter weather.”

 When oilseed rape is growing strongly with sufficient moisture, Andrew says crops will generally grow away from slug damage easily.

 But, if growth is struggling in any way, due to lack of water or nutrition, poor rooting or pest damage, crops can remain vulnerable to slugs for longer.

 Indeed, with several reports of cabbage stem flea beetle damage occurring in crops in recent days, this could be a factor that restricts crop development in some hotspot areas, prolonging the period of vulnerability to slug attack.

Monitor crops closely

 Prophylactic applications of slug pellets are not recommended, so Andrew says growers must keep a close eye on at-risk crops, looking for signs of slug activity and damage.

 If numbers do build to a level that requires treatment, he favours using a quality, durable mini pellet, providing a high number of baiting points, to maximise the chances of slugs encountering a pellet before the crop.

 Certis Belchim’s Colin Mountford-Smith says Menorexx ferric phosphate ‘mini’ pellets are a good option for growers wanting to achieve more baiting points from a lower overall dose.

 “They’re particularly effective for smaller juvenile slugs early in the season.”

 Application rates vary from 5-7 kg/ha, depending on slug pressure.

Baiting points

 At the lower rate, Colin says Menorexx pellets deliver 67 baiting points/m², compared with 42/m² from the larger Sluxx HP pellets, which he suggests switching to later in the season when conditions become more challenging.

 “When changing between pellet sizes, always make sure your applicator is properly calibrated,” he advises.

 Certis Belchim’s online Slug Pellet Calibration Wizard (https://certisbelchim.co.uk/calibration) helps users do this and their Slugwatch decision support tool provides postcode specific weekly forecasts of slug activity indicating upcoming risk to crops.

 See https://certisbelchim.co.uk/crop-focus/slugs/slugwatch-forecast.