Assessing the leaf blotch disease complex in wheat:

A challenge for loss estimation and evaluation of warning systems

Andrea Ficke, Morten Lillemo, Unni Abrahamsen, Oleif Elen and Guro Brodal

How much yield do we loose from leaf blotch diseases?

Why relevant?

Justify our projects: Grant application

Determine the economical threshold for spraying

Rule of thumb: 1% severity = 1 % yield loss

Winter wheat Spring wheat

Know your enemy…

Fungicide trials:

•8 years, •2 different locations,•Different varieties,•Same assessment protocol (25 plants, last 2-3 leaves, at Z 70-80)•Yield data •Different severity levels•Yt-Yu= b (Dt-Du) (Bhatal et al., 2003)

Yield increase with LBD reduction

WHY ?

Units? Kg/daa, hLw, or TKW?

Difference between varieties?

Different groups of disease reduction?

What leaves to choose?

Timing of assessments?

What diseases involved?

Difference in varieties….

Yield increase/severity reduction ratio

Demonstrant

Yie

ld incr

ease

(%

)

LBD severity reduction (%)

Data from leaf assessments

% LBD infection/browning

HeadingIn boot

Z75

Leafblotch Disease Complex (%)Sem

10% lessyield

x

What other diseases are involved?

Powdery mildew (B. graminis) early

Fusarium Head Blight (Fusarium spp)

Conclusions:

There is no defined relationship between LBDseverity and yield reduction in Norway

Experiments need to be designed to addresstrue crop loss estimates

Timing and tissue are critical for assessment

All diseases involved need to be considered

Time until harvest…

Thank you!