Sugar Beet Pestwatch

Dow AgroSciences UK regularly undertake sampling and monitoring of Leatherjacket populations throughout England and Scotland. The studies are carried out in conjunction with ADAS in England and SAC in Scotland. Pestwatch bulletins are prepared from the results and normally issued in March to alert sugar beet growers to the potential for damage from Leatherjackets to the newly-drilled crop.

The most recent Pestwatch Report:

LEATHERJACKETS 2006

Mean leatherjacket populations in England were high in comparison with recent years. In midlands and northern areas they were the highest recorded in the period 1991-2005. In southern areas they were the highest since 2001. The data indicate an overall high risk of damage to susceptible crops after grass.

From the 47 sites surveyed in England during autumn 2005, 83% contained populations greater than 50/m², i.e. exceeding the advisory threshold above which damage to following spring cereal crops and sugar beet is possible. (34% last year)

A total of 165 fields were surveyed in west and central Scotland between November 2005 and January 2006. Leatherjacket numbers were found to be extremely high across most surveyed areas. The average population density of 250 grubs per square metre is the highest ever recorded in 30 years of sampling. There is a potentially very high risk of damage to spring cereals and root crops following grass. There is also a real threat to grass yields in three-quarters of the fields sampled.

Leatherjacket populations in grassland this year are very high. The risk of damage is very high in most areas, especially Ayrshire, Bute, Dumfries/Kirkcudbright, Lanarkshire, Renfrew and Wigtownshire. Over 80% of fields sampled were infested with in excess of 0.6 million leatherjackets per hectare and 75% of fields sampled contained population densities above 1.0 million per hectare. Nearly 40% contained densities of more that 2.0 million per hectare.

The population threshold for treating permanent pasture is one million leatherjackets per hectare (100/m2). The thresholds in susceptible spring crops are:

Spring cereals	0.5 million leatherjackets per hectare (50/m²)
Sugar beet and other row crops	0.25 million leatherjackets per hectare (25/m²)

Please note: it is not possible to sample every county, so the figures from sampling sites should be taken as a representative guide only.

ACTION

The risk of economic damage from leatherjackets this season is significantly higher than in recent years for susceptible crops in England and extremely high in Scotland. Fields with a history of leatherjacket damage 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.

If treatment is justified use Dursban* WG at 1.0 kg per hectare applied in 200 to 1000 litres of water. Control will be reduced if temperatures are below 5°C as the larvae will move deeper into the soil profile.

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