Monitoring at GS30 (start of stem elongation)

1. At GS30 count the number of tillers in 50 cm row lengths (choose at least 5 areas of the paddock) (e.g. 433 tillers counted)
2. In the same row lengths count the number of tillers with symptoms (e.g. 43 tillers with symptoms)

   At this stage you will have 10% (0.1) tillers with symptoms (43/433).

3. In or around each of the five areas check 20 tillers with symptoms for the presence of Russian wheat aphid (RWA)*, total 100 tillers to be checked. (e.g. results = 54 tillers with symptoms and RWA)

   At this stage you have 54% (0.54) tillers with symptoms and RWA.

4. Multiply the percentage of tillers with symptoms with the percentage of symptomatic tillers that are hosting aphids. This will result in the percentage of tillers with RWA.

For example: 0.1 x 0.54 = 0.054 = 5.4% of tillers with RWA in the paddock at the time of observation.

*You may need to check at the base of rolled tillers to confirm presence of aphids (RWA is found almost exclusively on tillers with symptoms).

You can use the online calculator or a doubling rate of 35 days to predict if aphid density will reach the economic injury level by GS50.