Late sown spring barley crops are at high risk of Barley Yellow Dwarf Virus (BYDV) attack, Teagasc has warned.
Although in some parts of the country a proportion of crop was drilled about a fortnight ago, it has only been in recent days that growers in the north east have been able to get out into their fields.
According to Teagasc entomologist, Dr. Louise McNamara, aphid numbers will increase dramatically with the projected rise in air temperature that is now expected.
On the latest edition of the Tillage Edge podcast Dr. McNamara said:
“Aphids will be more active and will multiply quicker as conditioner become milder.
“The rate and optimal temperature for this to happen depends on the species. But the 170 degree days model provides a good rule of thumb.
“In other words every 170 degree days will see aphids doubling in number.”
She explained that this process involves taking 3 degrees away from the temperature recorded on a particular day and multiplying up by the requisite number of days.
For sample, 10 consecutive days of temperatures at 20 degrees brings the BYDV count up to 170 degree days.
Dr. McNamara confirmed that every aphid is born with the next two generations alive inside of them.
She said this means they have “the ability to reproduce in the field very quickly.”
The Teagasc entomologist also outlined that there are 25 species of aphids that can spread BYDV.
The three that give most cause for concern are the grain aphid, the bird cherry-oat aphid and the rose grain aphid. Each has different main hosts and they will also alternate hosts, depending on the weather.
Dr. McNamara said: “The grain aphids will probably have come from cereals or grasses The other species might well come from woody hosts, so it depends.
“Reports are coming in of some winter cereal crops that have been quite heavily impacted by BYDV.
“For the most part, this was a direct result of farmers not being able to get out into the fields last autumn. But, thankfully, this is not the situation in the majority of cases.”
During the latest Tillage Edge podcast it was highlighted that the 2023 spring planting season can be split into three broad categories:
- Very early sown crops that were put drilled in February;
- A very small proportion that was sown out during March;
- The bulk of this year’s crop that has gone into the ground over recent days.
According to Dr. McNamara, the threat of BYDV is very much temperature linked.
She has indicated that the cooler the conditions, the less active that aphids will be.