With recent low risk years, levels of the pest orange wheat blossom midge (OWBM) are expected to be minimal in 2012 but growers must still be vigilant, experts warn.
Lower activity of the pest in past seasons, combined with resistant varieties, has resulted in fewer larvae dropping to the soil to lay dormant in cocoons, where they can survive for up to 10 years.
Despite the potential of another low risk year, Steve Ellis, entomologist at ADAS explains that if conditions are right and midges emerge from the soil simultaneously, treatment may still be required.
“No soils are currently above 11C so it is a little too cold for activation, but if those temperatures rise and coincide with the susceptible period during ear emergence (GS53-59), we could still have a problem.
“ADAS, in conjunction with Dow AgroSciences, will have sampled soils at 15 sites around the UK by 15 May and we will look at levels of the pest; results should be published on the Dow AgroSciences website a week later.
“The samples hope to discover if the pupation period has started, which will mean that growers will only be one step away from getting active midges and should prompt growers to start trapping to monitor threshold levels,” says Dr Ellis.
Growing OWBM resistant varieties is the simplest way of removing the risk of yield losses from the pest. However, chlorpyrifos remains the key chemical control, with more persistency than other products and activity on eggs.
Integrated Pest Management
The potential loss of approval for chlorpyrifos would have serious implications for the control of important arable pests, including OWBM, so growers are urged to use pheromone traps and thresholds to avoid unnecessary spraying.
“They are a very effective decision support tool, at a time when farmers are extremely busy. It is a notoriously hard pest to keep track of as it varies from year to year and can be localised,” says Toby Bruce at Rothamsted Research.
Dr Bruce points out that the last bad year for OWBM was back in 2004, with an estimated £80m of damage to wheat crops from the pest that year.
“With the current price of wheat, any significant attack from the midges could be economically devastating and the worry is that following a number of years with little occurrence, it may not be at the front of people’s mind.”
Thresholds for the pest are on two tiers. If more than 30 midges a trap a day are discovered it indicates a threat, which should prompt growers to walk crops and count midges visually.
“Milling varieties should subsequently be treated if there is one midge for six ears and feed varieties one midge for three,” explains Dr Bruce.
“If there are more than 120 midges a trap a day then treatment should be immediate,” he adds.
Traps should not only be placed in susceptible crops, but also in cropping areas that follow wheat, particularly second or continuous wheats where larvae in the soil could have built up.
If industry can abide by the rules, chlorpyrifos should be available for the foreseeable future, says Will Foss, agronomist with Agrii. “If we don’t we’ll either lose it all together, or be forced to use 75m buffer zones, which is just impractical.
“If I am confident of getting the timing spot on, I would use a pyrethroid such as Mavrik (tau-fluvalinate) which has a much better environmental profile and will have less impact on natural predators,” says Mr Foss.
“But where chlorpyrifos must be used, stick to the correct nozzles and ensure they retain their LERAP three star rating by maintaining the correct pressure, boom height and ground speed.”
The new stewardship initiative launched by the three approval holders for chlorpyrifos aims to protect the active ingredient through good spraying practices when applying the chemical.
The aim of the initiative is to have 100% of sprayer operators using LERAP three-star rated low drift nozzles when applying the insecticide, with a recommended buffer zone of 20m around watercourses.
The campaign website has just released a nozzle advice card which is now available to download from the website, but is also being mailed to farmers. It will assist operators in their nozzle choice when applying chlorpyrifos.
The “Say No to Drift” campaign stand will be at the Cereals event this year at Boothby Graffoe, Lincolnshire, where experts will discuss nozzle selection and the practicalities for growers and operators. A possible two BASIS and two NRoSO CPD points are available for attendees.