1. Spatial variation of weed density in a small cereal field Therese With Berge

2. PhD student, Herbology, Plant Protection Centre, The Norwegian Crop Research Institute (3.5 yrs) Research Assistant, sub Arctic vegetation/remote sensing, N Sweden (1998-2000) MSc Arctic Plant Ecology/Remote Sensing, Univ. of Tromsø (1998) www.planteforsk.no My background

3. PhD work Defining/improvement of broadleaf weed damage threshold models in spring cereals Competition experiments at field scale Weed position mapping – geostatistical analysis

4. Spatial variation of weed density in a small cereal field

5. Why? Weeds are often heterogenously distributed Herbicides should be applied only where needed Detection and spraying at same time

6. Specific questions: How close should measurements of weeds be taken in the driving direction? How wide can a presicion spray boom be?

7. Methods Counting within frames Geostatistical analysis

8. Mapped site

9. 0.5 m

10. Semi-variance analysis see e.g. Noel A.C. Cressie (1993)

11. Variogram models Exponential if h = 0 if h > 0

12. Akaike’s information criterion (AIC) (see e.g. Webster & Oliver 2001)

13. Prelimnary results 010203040 0.0 0.2 0.4 0.6 0.8 distance semivariance WLS,exp,25m ML,exp,full (h) AÎC -30.7 -68.8 RpRp 27 21