Barley yellow dwarf virus (BYDV) tool for cereals

Aphids can transmit barley/cereal yellow dwarf viruses (BYDV) to cereal crops. Decision support tools can indicate high-risk periods and guide management interventions.

Use decision support tools alongside local knowledge and risk attitudes to determine treatment requirements.

Aphid T-sum tool

This tool predicts aphid development (rather than BYDV risk directly).

Initially, aphids colonise relatively few crop plants. However, the second (wingless) generation tends to move away from the plant originally colonised. Controlling this generation is a key part of a BYDV management strategy.

This tool calculates accumulated daily air temperatures above a baseline temperature of 3ºC (the T-sum) from the start date (either on the day of crop emergence or after a pyrethroid application).

The second generation may be in the crop when accumulated temperatures (blue line) reach 170ºC.

When the shading changes from green to red, it indicates that the T-sum is above 150ºC (this is when frequent crop monitoring should start).

On the map, click on a site circle (and hover the mouse cursor over it) to see the corresponding T-sum data.

Click on the ‘Aphid flight activity’ button to see the amount of time with temperatures above 11ºC (aphid flights are limited under this temperature).

Note: The tool activates in autumn (from 1 September).

T-sum tool notes

Observed weather data covers up until yesterday.

Forecast weather data covers today and the next 48 hours.

Please account for insecticide product persistence (see label) when setting the start date following a spray.

Simple example of a T-sum calculation:

Day one (start date): 15ºC minus 3ºC = 12ºC
Day two: 15ºC minus 3ºC = 12ºC
T-sum for days one and two = 24ºC

The tool assumes:

Aphids are present at the start date
All aphids carry BYDV
The crop is sprayed at T-sum 170ºC (after which the T-sum resets to 0)

This interactive T-sum tool was first released in 2018.

Although it is effective, it overlooks many factors that affect BYDV risk.

To compensate, it is conservative (compared to the BYDV tool) and tends to suggest more sprays than may be required to prevent unacceptable yield losses.

New BYDV tool (coming soon)

Cereal growers asked to help develop a new BYDV tool

Further information

Virus management in cereals and oilseed rape

Regional information on aphid numbers and viruses