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Virus vigilance

8 April 2013

The evolution of aphid and virus populations means GB is facing continued challenges to control the spread of virus in crops. The latest AHDB Potatoes research ensures growers are one-step-ahead.  

With 2013 crop planting underway, it won’t be long before growers and agronomists are considering aphid management this season. “It’s therefore a good opportunity to remind everyone of the resources that are available,” says AHDB Potatoes’s technical specialist Claire Hodge. 
 
AHDB Potatoes funds a network of 100 yellow water traps around the country. These are part of the Aphid Monitoring Service and are used to provide alerts of when the first Myzus persicae (Peach–Potato Aphid) appear. “Myzus persicae is an important vector of potyviruses such as Potato Virus Y (PVY), Potato Virus A (PVA), as well as other viruses such as Potato Leafroll Virus (PLRV),” explains Claire. 
 
“In the case of potyviruses, M. persicae is not the only vector, other aphids also transmit the viruses. The yellow water trap catches are used to provide index values that include information about the presence and abundance of these other aphids, as well as M. persicae”. 
 
Recent AHDB Potatoes-funded research has led to a change in the way these index values are calculated. The project has looked at the aphids that are capable of transmitting PVY and PVA and studied whether some aphid species are better at transmitting potyviruses than others. 
 
It was already known that there are differences between aphid species and Relative Efficiency Factors (REF values), which reflect how well aphid species transmit potyviruses, are used to calculate the index values from yellow water trap catches. 
 
“However, aphid clones and virus strains change over time and we wanted to review whether any REF values needed updating” says Claire. The results from the project led to a change in one of the REF values used in 2012.
 
“The Willow–Carrot Aphid,  Cavariella aegopodii, was shown to be much more efficient at transmitting PVY than previously thought and a new, higher REF value for this species was used in the calculation of index values in 2012”.  Now for 2013, the REF value for another aphid, the Grain Aphid, Sitobion avenae is being revised upwards. 
 
The table shows the species whose transmission efficiency values have been upgraded on the back of the comprehensive testing. 
 
The transmission efficiency of a different aphid species in relation to the PeachPotato Aphid, Myzus persicae
Aphid species

Number of aphid clones tested

Current PVY REF value

Revised PVY REF value

Acyrthosiphon pisum (Pea Aphid) 3 0.70  
Aphis fabae (Black Bean Aphid) 3 0.01  
Brevicoryne brassicae (Cabbage Aphid) 2 0.01  
Cavariella aegopodii (WillowCarrot Aphid) 2 0.00 0.50
Drepanosiphum platanoidis (Common Sycamore Aphid) 1 0.00  
Hyperomyzus lactucae (BlackcurrantSowthistle Aphid) 1 0.16  
Macrosiphum euphorbiae (Potato Aphid) 3 0.20  
Metopolophium dirhodum (RoseGrain Aphid) 3 0.30  
Microlophium carnosum (Nettle Aphid) 2 0.00  
Myzus persicae (Peach–Potato Aphid) 3 1.00  
Rhopalosiphum padi (Bird Cherry–Oat Aphid) 3 0.40  
Sitobion avenae (Grain Aphid) 3 0.01 0.60
 
The Grain Aphid, is now considered a much higher risk and the REF value for PVY has been increased from 0.01 to 0.6 for this species. So depending on the numbers of S. avenae in a region, growers may see higher index values being reported for this season. 
 
The research results have also shown that S. avenae, the Black Bean Aphid, Aphis fabae and the Potato Aphid, Macrosiphum euphorbiae, are efficient vectors of PVA. Therefore growers of PVA susceptible potato varieties should take this into account or consult their agronomist.
 
These revised values will now be part of the calculations when warnings are issued by the Aphid Monitoring Service. The information is collected on a weekly basis and advice on virus risk to crops is updated daily at http://aphmon.csl.gov.uk  Signing up to aphid alerts will warn you of high risk scenarios in your area or nearby. 
 
Another of source of information about aphid flights is the network of suction traps in England and Scotland. These traps are emptied daily and provide regional information on aphid numbers, where the yellow traps provide more local information. The data from the suction traps are made available via:
 
The combination of warnings and practical advice on the AHDB Potatoes website allows management decisions to be made based on current aphid pressure and local findings. “This could be to modify aphicide programmes or a change to burn down dates,” adds Claire. “Pyrethroid resistance found in the Grain Aphid, S.avenae, is a sign that a more targeted aphid control programme is required for sustainable virus control.
 
The AHDB Potatoes-funded research project has looked at a number of factors that influence virus transmission, not just the aphid vectors. The final report will be published at the AHDB Potatoes website soon. In the meantime, practical recommendations for the season include: 
 
Virus management through classification and certification: Analyses of classification scheme data from Scotland indicate that crops with virus observed during the previous season are four times more likely to exhibit virus symptoms than those crops in which virus was not seen.  Therefore, sourcing clean seed stocks is an important part of any virus management programme. This can be achieved by using certified seed or, if using farm-saved seed inputs, ensuring these are virus tested.  
 
Roguing: This will be more critical for stocks derived from seed in which virus symptoms were seen the previous season, i.e. eliminating as much of the virus inoculum inherent within the seed stock as soon as possible.  
 
Other crops: It is also important to be aware of crops in adjacent fields because of the implications for the presence of virus vectoring aphids. Cereal aphids appear to be efficient transmitters of virus and can migrate from cereal crops in significant numbers. 
 
Groundkeepers: Management of groundkeepers is important to reduce external sources of potyvirus inoculum. 
 
Sign up for aphid monitoring alerts: These are provided by the AHDB Potatoes, Fera and SASA and are available via e-mail, SMS text and through the AHDB Potatoes website at http://www.potato.org.uk/online-toolbox/aphid-monitoring.
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