Seasonal influences on aphid populations
As featured in Arable Farming Magazine
Seasonal influence on aphids
by Arable Farming Magazine March issue
The BeetTech22 meetings gave growers a taste of just some of the research emerging from the British Beet Research Organisation to help in future-proofing sugar beet crops. Alice Dyer reports.
The first two sugar beet seasons without insecticidal seed dressings were in stark contrast.
In 2020 virus struck 38% of Englands crop on average, reaching 67% in some areas near Wissington, Norfolk, compared to just 2% of the crop in 2021.
This was all down to the weather, with several cold weather events of -6degC seen last January and February.
This is the best insecticide, Prof Mark Stevens, head of science at BBRO, told the Newark BeetTech22 event.
Last year, aphids were six to eight weeks later, some came in June versus early April in 2020.
There was also a huge difference in aphid numbers between the years, with an average of 470 aphids per site in 2020, compared to just 15 aphids per site in 2021.
The low virus levels seen last season as a result could help to reduce levels of virus this year if aphid numbers are high, Prof Stevens added.
After 2021 weve seen less national incidence of virus, which means potentially there is a lot less inoculum overwintering into spring 2022.
Hopefully this helps to reduce the number of virus-carrying aphids.
Aphid numbers for the 2021 autumn migration period in East Anglia were relatively low, according to BBRO aphid monitoring, with just a slight uptick in mid-November.
Prof Stevens said: As it stands, I dont anticipate lots of virus carrying aphids we know infectivity is only around 1% but we must not forget what happened before for 2019-2020.
When we get these climatic conditions, aphids can build up very quickly once we get into the season, so keep an eye on the information.
New options for aphid control
As well as the possible use of a neonicotinoid seed dressing for the 2021 season, there are additional changes to aphid control programmes.
The insecticide InSyst (acetamiprid) from Certis has received full authorisation for use on sugar beet crops to help combat virus yellows.
Last year it was granted emergency approval which meant due to Defra restrictions, Teppeki (flonicamid) had to be used first.
However, now the insecticide has received full approval, InSyst can be the first spray in the programme Prof Stevens said.
At the time of writing, industry was still awaiting confirmation from CRD regarding whether InSyst could be used alongside the Cruiser SB (thiamethoxam) neonicotinoid seed dressing if the Rothamsted aphid threshold was triggered.
However, with some 50% of growers estimated to have ordered untreated seed, it will still play a valuable role this season in keeping aphids at bay.
Laurence Power, technical manager at Certis said: InSyst provides rapid knockdown, which is very useful early in the season to prevent early virus build up, which has the greatest impact on yield.
Mr Power advised growers use BBRO/Rothamsted and Warwick Universitys aphid monitoring services to keep track of aphids in the local area.
As soon as you hit that threshold of one green wingless aphid per four plants before reaching 12 true leaves or one per plant from 12-16 true leaves then its time to spray.
The rate of application should not be lower than specified to ensure good control and to prevent the likelihood of resistance build up.
For the best efficacy, make sure you check your water quality too insecticides in general do not like hard water.
The latest timing of application is 28 days before harvest.
Following an application to sugar beet between BBCH 12-19, InSyst must not be applied to the same field until the second spring, regardless of crop.
InSyst offers around 14 days of protection, depending on the weather.
If the threshold is met again, growers also have the option of one application of Teppeki.
BBRO is also working with NFU Sugar and British Sugar to submit an application for emergency authorisation of a third aphicide, particularly for crops that have not been treated with Cruiser.
Natural enemies such as ladybirds, ladybird larvae, lacewing, ground beetles and spiders all have a role to play in managing aphids, but timing is the greatest challenge.
Prof Stevens said: The most important thing is having them in the crop at the same time.
Clearly in 2020 we had aphids from the end of March until June, but the beneficials didnt show in the crop until the beginning of May, so it was very out of sync and consequently aphids were left unchecked.
Last year was very different and they were there at the same time and we saw the benefits of that.
Anything you can do to encourage any beneficials is important.
A small number of growers saw success with a barley cover crop camouflaging sugar beet until it was established.
However, its important to make sure you destroy it at the right time so you dont lose out on yield, he added.