The mild and wet conditions that have dominated the first three months of 2024 could culminate in a perfect storm for BYDV (barley yellow dwarf virus) infections in spring barley.
That is the warning from Dr Bill Lankford, herbicide and insecticide technical specialist at ADAMA, who explains that an early aphid migration is predicted to coincide with when crops are at their most vulnerable.
The latest modelling work from Rothamsted Research suggests that the first flights of Bird cherry-oat aphid (Rhopalosiphum padi) are predicted to take place in the first half of April in England, with Grain aphid (Sitobion avenae) and Rose-grain aphid (Metopolophium dirhodum) expected to follow soon after.
“That’s two to three weeks earlier than normal, with the number of aphids also predicted to be in the top 25% of historical levels,” Dr Lankford says. “As such, there’s a high risk that barley plants could become infected with the BYDV virus almost as soon as they emerge from the seedbed, with subsequent aphid migrations exacerbating the problem by spreading the virus further into the field.”
In England, the first aphid migration of the year rarely threatens spring barley, as crops are usually far enough ahead that they have advanced beyond their most susceptible 2-5 leaf growth stage. However, the mild start to the year has seen temperatures rarely below the minus 5°C needed to reduce aphid populations.
“The majority of spring barley would normally be sown and out of the ground by the end of March, large areas are still to be drilled, leaving a significant potential for aphids to find and infect new seedlings as soon as they emerge,” he notes.
To protect yields, and the potential for crops to attain a malting premium, he is advising growers to factor a suitable aphicide treatment into their early season spray programmes.
“In Ireland, where the convergence of aphid activity and crop emergence occurs more frequently, yield losses of 0.5-1.0 t/ha are commonplace in untreated crops, so it’s worth protecting crops from the outset,” Dr Lankford continues.
Assuming the aphid population threshold is exceeded, the best line of defence is to apply an insecticide when the crop is at growth stage 13-14, with Dr Lankford recommending the use of a pesticide with a lower impact on the beneficial insects which feed on and, therefore, help to control pest populations.
“In situations where a pyrethroid pesticide is deemed necessary, MAVRIK® (240 g/litre tau-fluvalinate) not only provides fast-acting contact control of aphids in cereals, but also has a lower residual impact on beneficial insects compared to other pyrethroids,” Dr Lankford explains.
“This reduced toxicity enables populations of advantageous insects such as ground and rove beetles, hoverflies, lacewings, ladybirds and parasitic wasps and flies to recover more quickly after crops have been sprayed, therefore ensuring there’s a strong population of predators ready and able to contribute to the control of any subsequent influxes of aphids. It also has the added advantage of being very fast-acting which means it halts feeding damage quickly.”
MAVRIK also remains stable at higher temperatures compared to alternative insecticides, he suggests. “Work carried out at BTL Bio-Test Labor Gmbh Sagerheide in Germany showed aphid knockdown and the persistence of MAVRIK continued to be robust at 20 and 25 °C which makes it the more effective option if and when the mercury finally starts to rise,” Dr Lankford concludes.
