2011 aphids outlook
2011 aphids outlook for seed potatoes
Following the exceptionally cold winter the Rothamsted Insect Survey (RIS) and SASA potato aphid forecasts for 2011 are for late flights and low numbers.
Rothamsted’s Dr Richard Harrington says predicted peach–potato aphid first capture dates at all 16 RIS and SASA suction trap sites in England and Scotland are over a month later than average.
Most seed crops in Scotland and Yorkshire are planted by the end of April and when they emerge in late May to early June should have about a month free of peach–potato aphid pressure. However, rose–grain aphids, which over-winter mainly as eggs rather than in mobile stages, will hardly have been affected by the harsh conditions so should be expected to start flying during May and build up to peak numbers in July as usual.
A significant early outcome from PCL-funded project R428 – ‘Aphids and virus transmission in seed crops’ – is that rose–grain aphids are the most likely vectors of the non-persistent viruses PVA and PVY. Last year some areas of Scotland were overwhelmed with them and the incidence of PVY symptoms recorded in crops jumped to over 15%.
Bayer CropScience’s Dr Bill Lankford says the implications for seed potato crops this year are; “In-furrow treatments should not be required as they are unlikely to persist through to the predicted late arrival of potato aphids. Growers will need to focus on control of cereal aphids for four to five weeks from crop emergence, and when the colonisers arrive, the twin threats will be best managed by alternating sprays of the systemic insecticide Biscaya (thiacloprid) with approved pyrethroids.”
Further early conclusions from project R428 are that mineral oils represent an untapped control method to prevent non-persistent virus spread and investigation of synergy between the new classes of insecticides including neonicotinoids is required. Given the shortage of highly effective control methods Dr Lankford expects growers will want to experiment with their use this year but warns;
“In tests so far with one mineral oil, adding it to Biscaya has produced phytotoxic effects and increased virus symptoms. This seems to be caused by disruption of Biscaya’s advanced O-TEQ oil dispersion formulation, which drives its fast uptake and persistence. Because of this result we can not yet support tank mixture with mineral oil and recommend Biscaya is used in alternation with other oil-containing treatments e.g. approved pyrethroids + mineral oil.”
An interesting consequence of last year’s record cold December is that the RIS 2011 potato and vegetable aphid forecasting method had to be revised. Dr Harrington explains; “forecasts have, in the past, been based on the mean temperature in January and February because this shows the strongest correlation with the timing and size of aphid migrations.
“However, it is unlikely that aphids which overwinter predominantly in mobile stages will have survived the very cold December so this year we have based the forecasts on the two coldest winter months; December and January. We wait with bated breath because if we had used January and February it would have been a very different story!” Growers are recommended to keep up to date with aphid activity through the season by visiting the RIS or SASA websites.
