News

Leatherjackets

 

Each Autumn Dow AgroSciences commission ADAS and the SAC Auchincruive to survey leatherjackets numbers in grassland sites across England and Scotland as part of its commitment to the Stewardship and product support for users product support for users of Dursban* WG and Equity*.

 

The latest survey indicates a very high risk in Scotland this Spring. In England there is an increased risk of damage in 2010 compared to last year, but overall the risk in all English regions is low.

 

All sites samples were in grassland. Results give an indication to the risk to susceptible crops including spring barley and sugar beet.

 

 

SCOTLAND

A total of 242 sites in west and central Scotland were sampled during November 2009 - March 2010. Leatherjacket populations have increased steeply from the low levels of the past two years.

 

Whilst the Threshold for likely damage in winter and spring cereals following grass is 60/m2, a lower population may cause damage to root crops.

 

The overall mean leatherjacket population was 124/m2, with 67% of sites over the cereal damage threshold of 6/m2; 51% were over 100/m2 and 19% were over 2/m2. Fields especially in Ayrshire, Argyll, Bute, Lanarkshire, Renfrew, Strilingshire, Perthshire and Wigtonshire are especially high risk. Only in Dumfries/Kirkcudbright does the risk appear to be low. 

 

Wet conditions in Scotland last July to September favoured egg survivaland larvae emergence at a time when they are vulnerable to dehydration. This wet weather and associated milder temperatures through the autumn were ideal for survival of eggs and growth of young larvae therby ensuring large number of larvae came through the adverse conditions experienced later in December and January.

 

 

ENGLAND

A total of 46 sites was sampled in the three key regions shown below during Autumn 2009.

 

The overall mean leatherjacket population was 16.3/m2 compared with 7.1m2 in 2009 and a long term average of 61.0/m2.

 

In the Midlands/Western Region comprising Cheshire, Shropshire, Staffordshire, Warwickshire and Herefordhire the overall mean was 16.2/m2 (mean 20 sites)

 

In the Northern Region covering North, South and West Yorkshire the overall mean was 18.0/m2 (mean 2 sites)

 

In the Midlands/Western 1% of fields sampled and in Northern  regions 5% of fields sampled had leatherjacket numbers in excess of 60/m2.

 

In the Southern Region of Berkshire, Hampshire and Oxfordshire the overall mean was 2.0/m2.

 

The survey suggests there is a low or very low risk of damage to susceptible crops in all English regions sampled.These numbers are probably a reflection of dry weather during September/October dehydrating eggs and young larvae.

 

Leatherjacket Damage Thresholds

0.3 million/ha (30/m2)        Population in W & Spr. Sugar beet etc. Likely to cause damage

>0.6 million/ha (60/m2)      Autumn grass population likely to cause damage in following cereals

>1 million/ha (100/m2)      Population in permanent grass likely to give economic benefit

>2 million/ha (200/m2)      Population in permanent grass likely to show visible damage

 

 

ACTION

The risk of economic damage from leatherjackets in 21 in Scotland is very high. Because leatherjacket populations will vary from field to field, risks should be assessed before treatment is made. Leatherjackets are very resilient to cold and frost; under such conditions they react by reducing their feeding ability until the soil warms up again. High infestations should be treated as soon as ground conditions permit and when leatherjackets are feeding.

 

In England the risk is low or very low. However, the risk has not gone away. Fields with a history of leatherjacket damage, particularly going into spring cereals, should be monitored for large numbers of rooks and crows feeding on the larvae. Risk assessments and testing for the presence of leatherjacket larvae will provide a good indication of fields that are most likely to need treatment.

 

Pre-ploughing treatments are more effective than those applied once damage is underway in the new crop.

 

If treatment is justified use DURSBAN* WG at 1.0 kg/ha applied in 200 to 1000 litres of water.

 

If using EQUITY* the recommended rate is 1.51 L/ha applied in 200 to 1000 litres of water.

 

Control will be reduced if temperatures are below 5oC as the larvae will move deeper into the soil profile.