Diagnosing frost in narrow-leafed lupins

Narrow-leafed lupins tolerate frost in early growth stages but are susceptible when growing rapidly from flowering to early pod fill.

What to look for

Low lying areas, light-coloured soil types, dry soil, and areas with more retained stubble are likely to be more damaged.

Plants with wilted upper foliage that shrivels and dies, or blistered pods.
These frozen upper stems become discoloured (dark green directly after thawing) and associated foliage shrivels and dies.
Often the damaged tissue (stem and pods) will take on a brown colour due to bacterial fungal infection.
Stems have surface splits that turn brown with a mushy interior.
Pods have pale surface spots or blisters and brown mushy lesions.
Developing pods abort and fall off.
Developing seed may abort.
Unaffected parts of the plant grow, flower and set seed if there is sufficient time and soil moisture.

Temperature

Frost damage occurs when night air temperature falls below -2°C.
Lupins become more susceptible throughout flowering and bud formation when the plant is rapidly growing.

Frost damage is irreversible however managing a crop to only avoid frost will come at a yield cost and potentially increased disease risk. It is advisable that after a frost event, to make note of the location and severity, as this will help to inform future crop choice and post frost decisions.
A comprehensive frost management strategy needs to be part of annual farm planning. It should include pre-season, in-season and post frost event management tactics.

Check low lying, light coloured soil types and known frost prone areas first. Then check other areas.
To identify frost damage check for gaps in pod set on the flowering spike and open pods that have a scarred surface to check for mushy, shrivelled or abnormal grain.