Vegetable Pestwatch
Cutworm
From the end of May and in to July each year, Dow Agrosciences, in conjunction with ADAS, monitor the population levels and life cycle progression of Cutworm. In-field observations and meteorological data are used to model the likely threat from Cutworms to developing vegetable crops.
Leatherjackets
Nationwide assessments of Leatherjacket populations are undertaken annually by Dow AgroSciences UK. Soil samples are taken from over 100 representative sites, from the south coast of England, through the south and west Midlands, the north-west of England, Yorkshire and from the west of Scotland.
The results of the surveys are expressed as the number of Leatherjackets per square metre and an indication of the potential for damage to susceptible crops is given. One Pestwatch report is published annually and is normally available in March, to coincide with the drilling of susceptible spring crops.
The most recent Cutworm Pestwatch Report:
| Preliminary Report |
Cutworm
|
11/06/04
|
Background
Cutworm is the name given to caterpillars of certain Noctuid moths, in particular those of the turnip moth Agrotis segetum. The older caterpillars feed underground, damaging plant roots and stems (including the storage organs that we use for food), sometimes so badly that the plant topples — hence the name.
The adult moths lay eggs on plants or on pieces of litter and debris in the soil. These hatch in around 8 - 24 days, depending on temperature, and then the young caterpillars seek out and feed on the aerial parts of plants. In a further 10 - 20 days, again depending on temperature, the caterpillars go through their second moult, becoming third instar caterpillars. It is at this point that they adopt the cutworm habit, becoming subterranean and feeding on roots etc.
Unhatched cutworm eggs and the older, subterranean caterpillars are largely invulnerable to the effects of the weather and insecticides. The two early caterpillar instars differ, however. If there is substantial rainfall (defined as 10mm or more of rain falling in showers of moderate intensity) whilst these caterpillars are feeding above ground then this causes a high mortality. They are also vulnerable to Dursban* WG whilst feeding on the foliage.
Crop Susceptibility
Crops differ in their susceptibility to cutworm damage. The most vulnerable are lettuce, leek and red beet. Cutworms easily bite through young lettuce and leek plants, and though beet plants may survive an attack the bulbous root is rendered unmarketable by cutworm feeding. Moderately susceptible crops include brassicas, carrot, celery, parsnip, sugar beet, and the least susceptible are onion, potato, swede and turnip.
Current Situation
Turnip moths have so far been caught in traps in Norfolk, Lincolnshire, Shropshire and Merseyside.
The rate of development of eggs has been steady in the reasonably warm recent weather. The earliest laid eggs have by now completed their development and begun to hatch. The most well-developed caterpillars have completed about 25% of their development and at current temperatures further development is occurring at about 10% per day.
Taken together, these factors indicate that there is currently a low risk of cutworm damage to any crops and no spray warning will be issued during the next week. Another Cutworm Report will be issued when action is necessary.
Action: Look out for the next Cutworm Report. Monitor larval survival by monitoring rainfall — 10 mm of rain or 20 mm of irrigation will kill cutworms. Be prepared to apply Dursban WG at 1.2 kg/ha in 600 - 1,000 litres of water once a spray warning is issued. No further action required at present.
Learn more about Cutworm
Learn more about Dursban WG
The most recent Leatherjackets Pestwatch Report:
LEATHERJACKETS 2005
Mean leatherjacket populations in England have shown substantial recoveries over the low populations recorded in autumn 2003 and 2002. The data indicates an overall increase in risk of damage to susceptible crops after grass.
From the 47 sites surveyed in England during autumn 2004, sixteen (34%) contained populations greater than 50/m2, i.e. exceeding the advisory threshold above which damage to following spring cereal crops is possible. Twenty-two fields (47%) contained populations exceeding the advisory threshold (25/m2) for crops such as sugar beet. In all counties that were surveyed, except Hampshire and Oxfordshire, fields with populations above this threshold were found.
A total of 149 fields were surveyed in west and central Scotland between November 2004 and January 2005. Leatherjacket numbers were found to be very high across most surveyed areas. There is a potentially very high risk of damage to spring cereals and a serious threat to root crops following grass. There is also a real threat to grass yields in almost half 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. Nearly 60% of fields sampled were infested with in excess of 0.6 million leatherjackets per hectare and 45% of fields sampled contained population densities above 1.0 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 considerably higher than in recent years for susceptible crops in England and very 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 5oC as the larvae will move deeper into the soil profile.
REGIONAL DATA
Midlands and North-West England
Based on the overall mean leatherjacket population, the potential for damage to susceptible crops following grass is expected to be higher than in 2003 and 2002.
Mean population in this region is considerably higher this year at 70.3/m2, compared with 13.1/m2 last year and 13.5/m2 the previous year. This year, 33% of fields sampled had a population greater than 50/m2. This compares with 0% and 4% of sites falling within this category in 2003 and 2002 respectively.
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Northern England
Based on the overall mean leatherjacket population, the potential for damage to susceptible crops following grass is higher than in the last two years in the northern survey area.
Mean population in this region has increased substantially from 12.5/m2 last year to 60.7/m2 this year, with 40% of fields sampled having leatherjacket populations greater than 50.0/m2. This compares with only 5% of sites within this category in 2003 and 0% in 2002.
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Southern England
Based on the overall mean leatherjacket population, the potential for damage to susceptible crops following grass is higher than in 2003 and 2002.
Overall, the mean population of fields surveyed in southern England was 30.0/m2. This compares with the exceptionally low mean values of 2.0/m2 and 0.0/m2 in 2003 and 2002 respectively. One field, in Berkshire, held a leatherjacket population above 50/m2.
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West and Central Scotland
Leatherjacket populations in grassland this year are exceptionally high. The risk of damage is very high in most areas, especially Ayrshire, Bute, Dumfries/Kirkcudbright, Lanarkshire, Renfrew and Wigtownshire.
Almost 60% of fields sampled were infested with in excess of 0.6 million leatherjackets per hectare and 45% of fields sampled contained population densities above 1.0 million per hectare. Over a quarter of fields sampled had in excess of 2.0 million leatherjackets per hectare. The mean population of leatherjackets detected has remained at a very high level (1.19 million/ha, same as last year) but with a greater percentage of fields in the highest risk categories.
