Last seasons patchy crops could have givenwheat bulb fly a helping hand, warn crop experts.
Adult flies lay their eggs onto bare orexposed soil in July and August, causing wheat being grown after fallow, viningpeas and root crops to be most at risk, rather than crops following oilseedrape or other cereals, they point out.
However, that situation could be differentin 2014, believe both Dr Steve Parker of Chemtura AgroSolutions and Dr SteveEllis of ADAS, who are concerned about the number of additional egg layingopportunities that were on offer in poorly established crops over the summermonths.
Theproblems that growers experienced last autumn means that we ended up with morepatchy crops and bare ground than ever before, giving wheat bulb fly anunexpected foothold during this time, says Dr Parker.
He adds that the pest has always beendifficult to predict and awkward to control, as its numbers fluctuateconsiderably from year to year. And egg hatch in the spring is dependent onsoil temperature, so there are a number of factors to consider when determiningrisk.
That unpredictable and sporadic nature ofwheat bulb fly was very evident earlier this year, reports Dr Steve Ellis ofADAS, who recalls that there were a large number of crops coming out of thewinter with just a single tiller at the time of egg hatch.
Based on egg counts, we had forecast a lowrisk year, he recalls. But the slow growth of crops suggested that they couldstill be susceptible to the pest, despite our earlier predictions.
However, most crops escaped unscathed, henotes. Many of the eggs hatched during foul weather, so we believe the larvaewere either frozen or drowned before they could find a home.
Wheat bulb fly is favoured by wet summersand delayed harvests, as these conditions encourage fungi to flourish in cerealears, providing a food source for the pest. The hot, dry summer might have beenless than ideal for the pest, but growers would be wrong to underestimate therisk, cautions Dr Ellis.
We will have a better idea at the end ofthe month when the HGCA field survey reports the wheat bulb fly populationsfound in Cambridgeshire and Yorkshire.
His advice is to treat late sown crops(November onwards) with an effective seed treatment, where egg numbers areabove a threshold of one million/ha. But crops sown from January to March mightbenefit from a seed treatment where there are less than one million eggs/ha.
In general, the risk is greatest when plantnumbers are sub-optimal and there are few tillers at the time of egg hatch.
Last year saw the introduction of Signal(cypermethrin) from Chemtura, extending the seed treatment options for wheatbulb fly and giving growers the chance to develop an integrated solution to theproblem, reports Dr Parker.
The withdrawal of dead-heart dimethoatesprays made it a very timely introduction. Growers are able to target thefields that are vulnerable to attack and reduce the need for foliar sprays byusing Signal.
Containing 300g/litre of cypermethrin,Signal can be co-applied with the commonly used fungicide seed treatments, headds.
Dr Parker also points out that work is alsobeing done to extend the Signal label to include wireworms.
That label recommendation already exists inFrance, so we are confident that we can produce the necessary evidence and datafor the UK.
A recent phenomenon is the term arablewireworms, as wireworm damage has been seen in situations where it wasntexpected, he notes.
Wireworms tend to be a problem thatpersists after taking long-term grassland into arable production, he says.But some researchers are seeing more widespread damage, so a label extensioncould be very useful.