Why leatherjackets are not root feeders |
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| Henk Vlug, zelfstandig entomoloog bij Insect Consultancy,
Wednesday 17 December 2025 |
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| 99 sec |
Leatherjackets have been studied for 340 years. This means that the earliest 'serious' publication about these larvae of crane flies was published as early as 1685 by a physician and natural scientist in Germany. At the time, he wrote that 'leatherjackets feed on the roots of turf'. This view persisted until it was definitively disproven in 1994: leatherjackets feed above ground on the green parts of the plant, regardless of whether it is a broad-leaved crop or grass.
| Leatherjackets on the green. Photo: Tristan van Dijken. |
In the second half of the previous century, leatherjackets were considered harmful and parathion (an insecticide) was routinely applied at a dose of two litres per hectare on grassland. This use was not based on an economic threshold for control on pastures and grass fields. In the second half of the 1970s, increasing concern about the environment created a need for an effective control threshold to curb indiscriminate use. A researcher at the Wageningen Institute for Plant Protection Research (IPO) was commissioned to carry out this project over a five-year period.
End of parathion use
Trials were set up at four locations in the Netherlands, at experimental farms (Regional Research Centres) in Friesland, Overijssel, Brabant and Utrecht. Four different doses of parathion were tested (0, 1, 2 and 4 litres per hectare). Each treatment was applied five times to obtain a representative picture. During the trials, observations were made on crop yield in kilograms of dry matter per hectare. It soon became clear that little or no economic damage was caused by leatherjackets, even at the zero dose. This marked the end of parathion use.
Burrow
The research also showed that leatherjacket populations increased once every seven years. Detailed field observations further revealed that leatherjackets live in a small burrow in the soil. At night, they emerge from this burrow to 'cut' the green parts of the grass above the growing point around the burrow. They then pull the grass blade into the burrow and only consume it there.
In the early morning, it was possible to see grass blades that had been 'cut' sticking out of the burrows and then disappearing again. Four different experimental studies were needed to convince other scientists that the assumption held for several hundred years was incorrect. Gradually, it became accepted that leatherjackets feed above ground on the green parts of grass and even die when fed a diet consisting solely of grass roots.
Incorrect information
Recently, an article appeared in the trade press about a new product to control leatherjackets. It claimed that leatherjackets feed on grass roots. The new generation of greenkeepers rightly looks to the latest developments in their profession. As a result, the old and incorrect image resurfaces as if it were true, especially since many English turf experts still refuse to accept that a well-substantiated Dutch study demonstrated the opposite.
 | | Henk Vlug |
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It is recommended that the current generation of greenkeepers and field managers take the time to carefully revisit the 'Handbook of turfgrass insects - Ecology and management', published in 2015.
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