Aphid numbers for the start of November are up on October counts and are also higher than this time last year.
However, no winged aphids were recorded – reducing the risk of the spread of barley yellow dwarf virus (BYDV).
According to counts by Teagasc (Oakpark), on unsprayed winter barley, there were an average of 16.3 aphids/m² recorded this week.
Aphid counts
No winged aphids were recorded in Oakpark last week. However, 67% of aphids were reported to be grain aphids – one of the species which spreads BYDV.
Source: Teagasc
Ground conditions were poor for sampling last week and just one aphid/m² was recorded, according to Louise McNamara – an entomologist with Teagasc. However, numbers were up to 15/m² in the third week of October.
Temperature, wind and rain can affect aphid populations. Using Oakpark weather data as an example, as this is where the counts were carried out, rainfall was significantly higher in October 2017 – an average of 52.9mm was recorded. 32.3mm was recorded in 2016. This may have contributed to lower numbers of aphids last year.
Air temperature was significantly lower on November 1, 2016 – a minimum of 1.7°C was recorded. A minimum of 6.5°C was registered on November 1, 2017. This may have also contributed to the drop in aphid numbers this time last year.
Aphid flight
BYDV is spread by aphids – aphid flight speeds up the spread of the virus. Therefore, winged aphids can lead to a rapid spread of the disease. However, aphids which are not winged can also spread the virus – but not at the same speed.
Optimum temperatures for flight are approximately 14-15°C. Frost this week should help to reduce aphid activity.
Control
Crops being sown from now on are at low risk from BYDV infection.
Crops planted with Redigo Deter seed dressing in October are still in the six-week control period. As temperatures reduce and aphid numbers decrease, there may be no need for an aphicide application – but conditions will need to be monitored.
Teagasc advice for September-drilled cereals is to spray in early November. This is as a follow up to either a seed dressing or a pyrethroid spray at the 2/3 leaf stage. However, ground conditions are proving difficult for spraying in some parts of the country.