1. Threshold vs. adjusted dosage Svend Christensen and Torben Heisel, DIAS Mark Paice SRI

2. Blackgrass (Alopercurus myosuroides)

3. Old Seed Bank Plants germinating Herbicide - use Stochastic Seed Mortality New Seed Bank Cost Stochastic Germination Economic Model Yield Loss Stochastic Weed Control Plants surviving Crop Weed Competition Seed Production and Dispersal Stochastic Seed Mortality Dose- response New Seeds Crop Weed Competition

4. Initial Blackgrass Data Blackgrass density was measured in a 14 m x 14 m grid in a winter barley at Silsoe Research Institute The model unit was 1 m by 1 m cells Treatment unit was 4 m by 4 m cells

5. Spatial weed management of Blackgrass The threshold algorithm PC-Plant Protection DAPS (Decision Algorithm for Patch Spraying)

6. The Threshold Algorithm If Blackgrass density was higher than 1 plant m -2 A normal dose of 3.5 l ha -1 IPU was applied

7. PC-Plant Protection A normal dose of 2.1l ha -1 IPU was applied

8. Input dataOutput data Point or zone model Competition model PC-Plant Protection Decision model DAPS - Decision Algorithm for Patch Spraying

9. Results Seed Bank

10. Seeds/m 2 Year 0 20 m

11. The Threshold Algorithm Seeds/m 2 Year 1 Seeds/m 2 Year 5 Seeds/m 2 Year 3 Seeds/m 2 Year 7

12. PC-Plant Protection Seeds/m 2 Year 5 Year 1 Seeds/m 2 Year 3 Seeds/m 2 Year 7

13. Decision algorithm for Patch Spraying Seeds/m 2 Year 1 Year 3 Seeds/m 2 Year 5 Seeds/m 2 Year 7

14. Yield loss (DKK ha -1 )

15. IPU dose (l ha -1 )

16. Cost (DKK ha -1 )

17. Model Assumptions The size of the treatment area affects the differences between the algorithm No spatially or temporally depended effect of soil conditions or cultivation factors on seed emergence, crop weed competition or seed production