Wheat Bulb fly Pestwatch

Report 2 – 22nd January 2015

Dow AgroSciences in conjunction with ADAS, are monitoring Wheat Bulb fly egg-hatch.

This pest tends to be a problem of the eastern counties from Essex to Yorkshire but can occasionally be a problem elsewhere. Wheat, barley and rye following fallow, potatoes, vining peas, sugar beet and onions are at most risk. Oats are not attacked. Many have delayed drilling until November to help control blackgrass.  Late drilled or backward crops where they only have one or two tillers at the time of Wheat Bulb fly egg-hatch in January/February are particularly vulnerable to damage. Crops sown after the end of March are unlikely to be attacked.

With many oilseed rape crops harvested particularly early last year, some farmers are concerned that their following cereals maybe at risk; however over many years the ADAS/HGCA survey has generally not found high numbers of Wheat Bulb fly eggs following oilseed rape.

Dimethoate sprays which were used for treatment when Wheat Bulb fly damage was seen are no longer approved so it is now even more important to identify fields which are of most risk. Treatment is now confined to preventative insecticidal seed treatments and/or treatment with chlorpyrifos (Dursban WG or Equity) at egg-hatch.

The latest HGCA Wheat Bulb fly survey indicated that only 1 field out of the 30 surveyed in eastern and northern England were above the 250 eggs/m2 economic treatment threshold for early/mid-autumn drilled crops. This is the joint lowest recorded since 1984. However, egg numbers in the north (Yorkshire) at 126/m2 were higher than in the east at 46/m2.

It’s likely that dry weather which allowed the 2014 harvest to proceed without delay, restricted the feeding ability of adult flies and this combined with low egg numbers in the previous two years has resulted in the low count.

For late November- March drillings, a lower threshold of 100 eggs/m2 is applicable. In the north of England, 53% of sites were above this level but, in the east of England, only 13% of sites were above this level.

The full survey results are available on the HGCA website www.hgca.com.

For egg-hatch monitoring, samples have been taken at the sites shown below where Wheat Bulb fly eggs were found in the autumn:

Progression of egg-hatch will be monitored over the next few weeks.

wheat bulb fly eggs


Hatch is underway in the east of the country but not yet in the north.  Values for percentage hatch in the east are probably over estimates in view of the low numbers of eggs recovered.  A greater volume of soil will be taken from these sites next week to try to increase the number of eggs extracted.

Site (19th January) Total number of viable eggs
(inc hatched)
Number of hatched eggs Percent of eggs hatched 
1. Ixworth, Suffolk 16 8 50.0
2. Terrington St Clement, Norfolk 3 1 33.3
3. Littleport, Cambridgeshire 6 0 0.0
4. Fimber, North Yorkshire 6 0 0.0
5. Huggate, East Yorkshire 9 0 0.0

It is not known precisely what initiates egg-hatch but is thought to be associated with diurnal fluctuations of more than 5oC between minimum and maximum soil temperatures.  It has been relatively mild, so probably we have yet to experience more widely the threshold difference between maximum and minimum temperatures.

What does this mean for you?

Dursban WG egg-hatch sprays are applied between the start of egg-hatch in January and its peak in February or March. These are most likely to be justified on high-risk fields, where egg numbers are known to be above 2.5 million eggs/ha. This may be in addition to any insecticidal seed treatment, if this has been used.

In the absence of egg counts for specific fields, risk assessments for treatment must be made on the basis of locality, previous cropping, drilling date, plant population, tillering and soil type. Use Risk Assessment Charts to identify fields at risk. Be prepared to apply Dursban WG at 1.0 kg/ha in 200 to 1000 litres per hectare of water at the appropriate time.

Equity® also has recommendations for Wheat Bulb fly.

An interval of 14 days must be observed between applications of Equity or Dursban WG and UNITE® or Broadway® Star, regardless of weather conditions. For Atlantis WG and similar approved formulations leave a longer interval of 4 weeks for crop safety.

For other compatibilies please refer to Equity or Dursban WG tank-mix advice. If necessary, Dursban WG

or Equity can be applied to frosty ground but should NOT be tank mixed.

Use low drift nozzles and extend buffer zones to preserve Dursban WG and Equity use.

For conventional boom sprayer:

  • Use LERAP – low drift – three star nozzles AND adopt a 20 metre no-spray buffer zone (1 metre for dry water bodies)

Visit Say No to Drift website


Previous reports

Spray window open for Kerb or ASTROKerb

There is still plenty of time to apply the residual herbicides ASTROKerb® or Kerb® Flo 500 in oilseed rape as the spray window doesn’t close until the end of January. This is a great opportunity to interrupt the lifecycle of black-grass with a chemical that works in a different way to those in cereals. Both products work well in December and right the way through to their cut-off date, the 31st of January.

Spraying OSR in Feb“Many growers see the need to look beyond one crop and plan a more effective black-grass control programme across their whole farm rotation. Kerb Flo 500 or AstroKerb both contain the residual active ingredient propyzamide that works in a completely different way on black-grass to the herbicides commonly used in cereals. So if these herbicides are used to their best effect in rape, there is a real opportunity to reduce the black-grass burden in following cereals. If application conditions are right, farmers can expect levels of black-grass control from AstroKerb or Kerb Flo 500 frequently in excess of 90%, a level that very few graminicides are currently achieving in any crop. We have seen successful results from AstroKerb and Kerb Flo 500 applied in throughout December and January,” says David Roberts of Dow AgroSciences.

“But conditions need to be right and applications should only be made with regard to water stewardship. In other words do not spray when there is any risk of run-off to adjacent watercourses,” warns David.

“Propyzamide in Kerb Flo 500 is soil-acting, so spraying wet weeds at run off or after light rainfall is not an issue. In colder conditions its activity is prolonged and because frosts cause black-grass to throw out more adventitious roots, there is improved uptake of propyzamide. Kerb Flo 500 can be applied in frosty weather. However do not spray onto frozen ground if rain is forecast as this could result in run-off into water courses. Precautions are vital in order to avoid contaminating water. AstroKerb, on the other hand, contains the residual propyzamide plus the contact-acting aminopyralid and so the broad-leaved weeds targeted, poppies and mayweeds, are best controlled when applications are made to a dry leaf. If it rains within one hour after application, efficacy will be reduced. For AstroKerb, wait until the frost is off the weed leaf and the leaf is dry enough.”

David has seen that if you spray Astrokerb in cold conditions, you need to be patient as weeds take a while to die. “Weeds only start to show symptoms and die when active growth recommences. You can also look out for the classic symptoms of propyzamide-affected black-grass, such as swollen stem bases and purple or reddening discolouration. Propyzamide is known to work slowly and it can take up to three months to kill weeds. The herbicide’s activity will not be affected by cold temperatures after application, however.”

He says that this year many oilseed rape crops have dense canopies, with very few crops opened up by frost as yet. “Trials with Kerb Flo 500 demonstrate that a full oilseed rape crop canopy at the time of application makes no difference to the final levels of black-grass control. Astrokerb has contact and root activity on its main broad-leaved weeds, poppies and mayweeds. In our trials, when crop canopies were large, control of these weeds was good. However if, despite our positive experiences you are still concerned, wait until the frost has opened up the crop canopy before you apply these residual herbicides, but do so before the cut-off date.”

David reminds growers that, in order to maximise the efficacy of the residual active propyzamide, soil temperatures need to be below 10°C and falling and the soil should be adequately moist. “You can check your local conditions using the web-based Postcode traffic light tool on the Dow main web site (http://uk.dowagro.com/kerb-weather-data/-), the LifeCycle web site (www.myfarmlifecycle.com) and also on Farming On-Line (http://www.farming.co.uk/), although I would think that most places across the UK now fall well within the right conditions.”

“The ultimate decision to spray must always be based on local conditions, including the ability to travel and the potential risk to watercourses. Maintaining careful Stewardship of residual herbicides in oilseed rape is vital to ensure the long term availability of these important herbicides,” says David Roberts.

Controlling poppies and grassweeds across the arable rotation

Poppy time to sprayIndependent agronomist Peter Riley looks beyond this year’s arable crops and plans a longer term assault on difficult and obvious weeds such as black-grass and poppies. He also saw a lot of sow-thistles and thistles on his travels last season, but not in East Anglia where he applied his longer term policy based on using propyzamide-based herbicides in oilseed rape.

Check out application conditions for your postcode

KWD banner imageThe popular and helpful on-line decision support “traffic light” system to aid the timing of both ASTROKerb® and Kerb® Flo 500 is now up and running. Uniquely data can be obtained by growers and agronomists at postcode level. This traffic light system works by reporting soil temperatures and soil moisture deficits in every individual postcode area across the UK.

Important label update for users of ASTROKerb

Dow AgroSciences is pleased to inform growers and advisors that CRD has granted an approval for ASTROKerb® to allow the straw from oilseed rape crops treated with ASTROKerb to be burnt for heat or electricity production. The following updated statement will now appear on the label : “DO NOT remove oilseed rape straw from the field unless it is to be used for burning for heat or electricity production.”