Leatherjackets are proving to be an issue on many farms this spring, warns SWFC’s Anthony Ellis
One of our clients recently got in touch about particularly severe leatherjacket infestation. Indeed, the farmer first thought something was up when he saw the crows and rooks flocking in certain spots on the field, having a feast.
Leatherjackets are the larvae of the crane fly (or daddy long-legs, as they are commonly known) and the grub can cause substantial damage to cereals and pasture. They become particularly apparent in the spring, feeding on plant roots as the soil warms, leading to the visible loss of crop and pasture.
The poor quality perennial ryegrass (PRG) ley (above) is going into its third season and is being hammered by leatherjackets. As you can see, the grubs are beginning to clear substantial areas of the field. Unfortunately, with no chemical solution available, it is now a case of understanding what went wrong and planning the future rotation around a known problem for this field.
A quick dig in the affected areas (above) revealed the extent of the infestation. The farmer had intended to take the ley out of pasture this summer/autumn, so we’re in discussion about what should follow. Clearly, spring cereals and grass reseeds will be out of the question for a year or two. But avoiding cereals and grass will also help to reduce egg-laying and break the crane fly life-cycle for the future.
But this is a good case study to talk about grass seed mixes and overall management. This field has been a straight PRG ley (not even clover), cut for silage and had a lot of slurry and bagged ammonium nitrate over the three years. As we can see from the images above, the result is poor rooting, bad surface and subsurface compaction and poor soil structure. This has all contributed to worsening the leatherjacket problem. Basically, a good example of how NOT to do it!
The Agricology website has an interesting free factsheet on non-chemical ways to control leatherjackets, following the results of a farmer-led field trial in Scotland.