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.
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|
|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.
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)