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Consequence for soils and slugs after late OSR harvest

The latest oilseed rape harvest for years, combined with widespread soil structure issues is setting the scene for another big slug year...

The latest oilseed rape harvest for years, combined with widespread soil structure issues is setting the scene for another big slug year if weather conditions also conspire to work against establishing crops at their most vulnerable.

“After the lessons from last year, when some growers didn’t even get autumn crops planted, many are going to want to drill straight away and get crops in rather than risk missing their opportunity again,” says Dr David Ellerton, Technical Development Director for Hutchinsons.

“But this risks missing out on the usual window of four to six weeks to devote to cultivations and soil repair, which can be a vital factor in deterring slug populations.

“A lot of slugs have already been seen about,” warns David. “The populations are so large that as soon as the conditions are right they come straight up to the surface and cause immediate damage to crops. Following the recent spells of heavy rain there is a lot of moisture in the seedbed and if soils aren’t in top condition then slugs have the potential to wipe out new crops when they are hardly out of the ground.

He adds that the trend towards modern varieties with low seed rates and the adoption of precision farming means there is little room for margin. “Every seed counts.”

Given that the cropping turnaround is nonetheless likely to be relatively fast, Dr Ellerton promotes careful assessment of slug pellet choice, especially in situations following oilseed rape that’s notoriously highly palatable to slugs. “Quality pellets based on ferric phosphate such as the wet process, pasta based formulation, Sluxx, or the high compression pellet Derrex will be key components of 2013 programmes,” he notes. “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,” concludes David.

Dr John Reade, Senior Lecturer in Crop and Weed Sciences at Harper Adams explains the vital importance of repairing soil structure prior to drilling. “Crops growing in poor soil structure are at an increased risk from pests and diseases, especially from slug attack,” he says. This will be heightened after the expected late drilling scenario. “Slugs thrive in poorly drained soils which are often a problem where the soil structure has not been maintained or repaired,” says John. “I would recommend improving the soil structure to reduce slug numbers then judicious use of slug pellets where trapping identifies a need.”

He adds that there are additional issues for crop establishment in general, namely poor germination, which will impede root growth, reducing a crop’s ability to obtain water and nutrients,” adds John.

 “Once a crop has been drilled there is little that can be done to address issues such as compaction, it is vital growers address soil structure issues following harvest.”

Improving soil structure should be an on-going process, says John. “Farmers should look to address this every year following harvest, rather than just acting once problems are established. Soil profile pits will help in identifying what needs doing.

“Sub-soiling at the correct depth will reduce compaction, and ploughing in the appropriate conditions will help to improve the structure of top soil,” explains John. “It will also impact the level of slug movement within the crop. If farmers attempt to cultivate when it is too wet this can result in more problems,” cautions John. “Timing and correct conditions are key.” 

 A further slug and soils related issue is that poor soil structure allows less movement of air and water. This can promote run-off, and that’s got concerning implications for the use of metaldehyde based slug pellets, where the active ingredient is being found in watercourses,” warns John.

David Ellerton believes this is a further reason for switching to ferric phosphate. “It is a logical decision and is a more flexible option for many.”

Crop residues are also a concern when it comes to establishing a new crop amid a slug threat, he adds. “Direct drilling and reduced tillage establishment techniques will leave more of the crop residue near the surface, providing a large fodder source for slugs. One answer is the utilisation of traditional plough based seedbed preparation methods ensuring crop residues are buried, and with subsequent rolling to consolidate the seed beds, this will all help to reduce slug movement towards germinating seeds,” concludes David.