Barley yellow dwarf virus (BYDV) is a yield-robbing disease in cereal crops including wheat, barley, oats, rye and triticale.

The amount of yield loss depends on the aphid activity, virus presence and strain, cereal growth stage at infection and climatic conditions. The principal vectors for transmitting BYDV are the bird cherry aphid (Rhopalosphum padi) and rose grain aphid (Metopilophium dirhodum).

Aphids acquire the virus by feeding on infected host plants like volunteer cereals or grass weeds. Once the aphid is carrying the disease, it takes between 12 to 48 hours before it can be transmitted to an emerging cereal. Aphids can also feed on crop roots, potentially transmitting the virus before the cereal has emerged.

The earliest symptoms of BYDV are discolouration of the younger leaves, with barley and wheat turning yellow, though there may also be purpling of upper leaf tips. Oats generally turn purple. As the season progresses, the plants will be stunted, showing extensive tillering, and delayed ear emergence and ripening. The grain will be of poor quality, and once the damage presents as patches across the paddock, the damage cannot be rectified.

The Foundation of Arable Research has launched a digital tool¹ to help growers make decisions around aphid management and advise on ways to prevent crop damage. The tools help growers predict when conditions are favourable for aphids to reproduce, and allows growers to monitor crops. If used in conjunction with aphid traps, this tool can be useful in identifying when to treat a paddock.

While there is no known resistance to pyrethroid insecticides in New Zealand, they are contact only and their limited persistence makes spray timing and targeting crucial. This places greater emphasis on alternative management techniques as outlined here.

BYDV management techniques¹

» Sow insecticide-treated seed.

» Destroy all green bridges four to five weeks before cultivating and sowing cereals.

» Delay drilling potential high-risk paddocks too early in the autumn.

» Select BYDV-tolerant varieties.

» Manage aphid numbers and spread before GS32 as the crop is less likely to be infected after this stage.

» Use an insecticide that will not harm beneficial insects.

» Rotate the insecticide mode of action to help prevent resistance from developing.

» Minimise general stress to plants with the appropriate use of trace elements.

» Strip tillage and minimal tillage benefits the natural enemies of insect pests as they live in the retained crop stubble.

» Use insecticides at full rates for the greatest knockdown and leeway persistence. Couple with an appropriate adjuvant for increased efficacy.

For assistance developing a management plan for barley yellow dwarf virus in your cereal crops, contact your local PGG Wrightson Technical Field Representative.

1 Foundation of Arable Research. (July 2022). A digital tool to identify when aphids are reproducing. Retrieved from https://www.far.org.nz/articles/1676/a-digital-tool-toidentify-when-aphids-are-reproducing.