Leatherjacket Survey

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General
Advice
Diary

General Description

Grub populations levels in grassland this year are very high and, the continuing cold weather will not have any impact on reducing grub numbers.

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The 2010 forecast:

Leatherjackets are very resilient to cold and frost and all they do under such conditions is reduce their feeding until the soil warms up again. Hence fields across the vast majority of areas (but especially Ayrshire, Argyll, Bute, Lanarkshire, Renfrew, Stirlingshire/ Perthshire and Wigtownshire) are potentially at high risk this year. Only in Dumfries/ Kirkcudbright, are grub levels (and hence risk) relatively low. With two-thirds of all fields sampled harboring populations greater than 0.6 million/ha, the risk of damage to spring cereals out of grub-infested grassland is very high. In addition, over half of the fields sampled contained population densities greater than 1.0 million/ha, and so many fields of permanent grassland are also at risk of serious damage and loss of yields (especially once the soil warms up and the grubs start feeding hungrily on grasslands which may be in poorer condition than normal because of the extended cold weather).

Summary of leatherjacket survey results 2002/03 to 2009/10

Survey	Mean	Percentages of fields in each population category
Year	Population (millions/ha)	Over 0.60 million/ha	Over 1.00 million/ha	Over 2.00 million/ha
2002/03	0.39	25%	13%	1%
2003/04	1.19	55%	37%	19%
2004/05	1.49	59%	45%	26%
2005/06	2.50	85%	75%	39%
2006/07	2.11	77%	63%	39%
2007/08	0.32	21%	8%	1%
2008/09	0.68	38%	26%	7%
2009/10	1.24	67%	51%	19%

Advice

Despite the potential threat to permanent grassland and spring cereals out of grass, uninformed insurance spraying is not recommended. Grub populations can vary, not only from area to area but also within an area and from field to field on the same farm. Consequently, even in years of high predicted risk, there will always be fields which contain lower levels of infestation. Hence it is essential that an assessment of leatherjacket densities is conducted prior to deciding whether any insecticide application is necessary. Conducting such assessments in late winter and early spring identifies fields at risk before any damage has occurred. If leatherjacket infestations are found to be high an insecticide should be applied as soon as ground conditions permit.

Given the continuing cold weather, it is particularly important to note that the activity of grubs (and hence the efficacy of the pesticides used to control them) can be reduced during periods of frost or when the soil temperature is below 5ºC. Hence for best effect, treatment should be timed to coincide with a period when there is likely to be a succession of days with no frost and higher soil temperatures. Pre-ploughing treatments are more effective than those applied once any damage is under way in the spring-sown crop. Assessment of leatherjacket infestations in individual fields can be undertaken by SAC as a chargeable service; details of costs are available from your local SAC Farm Business Services Office.

Leatherjacket population categories in grassland

Over 0.60 million/ha:		Density in grassland likely to cause damage in spring cereals out of grub-infested pasture
Over 1.00 million/ha:		Density in permanent grass at which economic benefit may be gained from insecticide treatment
Over 2.00 million/ha:		Density in permanent grass at which damage may become visible if no insecticide applied

Though not included above, populations much lower than 0.60 million/ha may cause damage to root crops drilled to a stand and to spring direct reseeds.

SAC received financial support from the Scottish Government and Dow AgroSciences UK Limited towards the cost of this survey and a proportion of the remaining costs were offset by the farmers involved having their fields sampled at a substantially discounted rate.

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