Test methods, insecticide resistance, mineral oils and monitoring: dealing with aphids in 2020 and beyond

Friday, 26 June 2020

The management of aphids particularly, those that transmit viruses, has been a focus of concern in recent seasons. We (virtually) sat down with our Crop Protection Senior Scientist for Pests Sue Cowgill to talk monitoring, testing and research projects that will help growers manage the issue.

Article:

Q: Growers have reported lots of aphid activity this summer, what are the reasons for this?

“The national suction trap network has been recording numbers of aphids for over 50 years. This data combined with the equivalent run of weather data has allowed researchers to establish relationships between weather and the timing of the start of aphid flights and aphid abundance in spring and early summer. The relationship works best for aphids which pass the winter in the active stages (as opposed to as eggs), this includes Peach–potato aphid (Myzus persicae) and Potato aphid (Macrosiphum euphorbiae). For these, the mean temperature in January and February appears to be key.

“Despite last winter being the 5th wettest on record and Britain experiencing several Atlantic storms, the air temperature was notably mild and the Jan and Feb temperatures were above average. This led researchers to predict early flights and the potential for higher numbers. “

Read more about AHDB Aphid Forecasts https://ahdb.org.uk/aphid-forecasts

Q: How can growers monitor aphid activity?

“The AHDB yellow trap network, which provides more localised information than the suction traps, has shown that the potential for higher aphid numbers has been borne out across most of the country, with some regions experiencing substantially higher numbers of Myzus persicae and /or earlier flights compared to the 10 year average. This aphid is considered the best vector of the main potato viruses and is also known to have resistance to pyrethroids.”

View the AHDB Aphid Monitoring Network https://secure.fera.defra.gov.uk/aphmon/

Q: Concerns about the management of aphid vectors had already been raised in 2019, and is expected to continue to be a concern, due to the ongoing reduction in the number of effective insecticides registered for use on potatoes and other crops. Are there alternative options for growers?

“In light of the concerns, AHDB has begun work on the management of aphids with the aim of reducing virus transmission. In 2020, this includes a trial in Cambridge which is focussing on whether approaches to virus management reported from other countries can be effective in GB.

“The main focus is on the use of mineral oils. These are widely used in mainland Europe and Canada. Research from Canada indicates that the number of days between planting and the first application of oils/spray programme is a significant factor affecting PVY spread in their system. In previous AHDB funded work on spray oils carried out several years ago, applications began at 75% emergence, whereas the information from Canada and France indicates that applications from 30% emergence are more common. Therefore, the 2020 trial includes a comparison of oils applied from 30% emergence and a standard spray programme. In addition, there are plots to evaluate whether an intercrop species or a straw ground mulch in addition to mineral oil applications offer potential to give further reductions in virus incidence. Physical amendments like these have been shown to have an additive effect to oil applications in reducing virus incidence elsewhere in Europe.

“It had been intended to have a duplicate trial evaluating the same treatments in Scotland in 2020 but due to the implications of the Corona virus-related restrictions the decision was made to postpone the trial until next season.

“Our Strategic Potato Farm East, at James Fosketts Farms in Suffolk will also be hosting trials to evaluate aphid/virus management. These complement the work at Cambridge, and involve more extensive comparison of the rates and frequency of mineral oil applications in conjunction with a standard spray programme. Tune in to our webinar: Strategic Potato Farms – research into practice to hear more on that work. If you miss the webinar you’ll be able to view a recording.”

Webinar: Strategic Potato Farms – research into practice.

Q: There are two main test methods for virus in potatoes, can growers trust both equally?

“In January 2020, AHDB and NFU convened a virus forum that brought together all parts of the industry to discuss the concerns that had arisen from the 2019 season. Technical issues that were discussed included commercial testing for viruses. From the research sector there was a consensus that:

    • Ideally sample after burn down before harvest.
    • Sampling must be representative
    • Use a W or grid pattern across the field
    • Take one tuber per plant, of representative size
    • It is less good to sample from boxes, but if it is necessary, take a sample from at least 10% of boxes.
    • The number of tubers needed per sample will be specified by the testing lab. But is usually a minimum of 100 tubers

More information on testing and interpretation of virus test results is available able on the AHDB aphid-virus pages https://ahdb.org.uk/knowledge-library/aphid-and-virus-potatoes

Q: Can anything be done about Insecticide resistance?

“Another concern discussed at the AHDB/NFU forum that is being addressed is the insecticide resistance status of important vector species.

AHDB, BBRO and various crop protection and agronomy businesses support an insecticide resistance monitoring project. This tests samples of M. persicae for evidence of any shifts in sensitivity to actives that are currently effective in providing control. It also provides information on the frequency of the known resistance mutations, for example those conferring resistance to pyrethroids.

“We are keen to obtain as a wide a geographical spread of M. persicae samples as possible and are keen to receive more samples from Northern England and Scotland. In addition, in 2020 the researchers are asking for samples of willow-carrot aphid. This aphid has been tested as part of the project in recent years but the results have been variable and more samples are needed to get a better picture of its sensitivity to pyrethroids.

“More information on submitting samples is available on the AHDB/IRAG page. As Rothamsted Research staff are currently not fully returned to lab work, anyone able to submit samples is encouraged to contact Steve Foster by email to arrange receipt of samples.”

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