Diagnosing group B herbicide damage in narrow-leafed lupins

Sulfonlyureas, imidazolamines and sulfonamides are systemic herbicides that are used for pre and/or post emergent grass and/or broadleaf weed control in cereals and are highly toxic to lupins. Damage can be caused by soil residue or spray contact.

What to look for

Paddock

Residual herbicide damage shows as stunted plants with yellow new leaves.
Residual damage is more likely on more alkaline (sulphonylureas) or acidic (imis) soils
Spray tank contamination causes similar damage that is more uniformly distributed but varies with spray coverage on overlaps or boom turns.
Spray drift damage is usually worse near the source, with similar symptoms

Plant

Soil residual herbicide damaged plants germinate normally but emerging leaves are yellow and plants are stunted.
Discoloured leaflets develop brown necrotic spots on the edge and tips then slowly die.
Plants are severely stunted and slowly die.
Seedling lateral roots are severely stunted.
Plants sprayed at later growth stages develop similar symptoms to new growth, and may take weeks to die. These plants are also often more affected by brown spot.

Where does it occur?

Chemical breakdown in soil is inhibited by high pH for sulfonylureas and low pH for imidazolinones.
Stressed plants are less able to metabolise herbicides and therefore more susceptible to damage. Stressors include drought, cold, wet weather, waterlogging, deep sowing, frost, nutrient deficiency and soil compaction.

How can it be monitored?

It is important to observe withholding periods for these herbicides to avoid damage to following crops.

Further information

HerbiGuide [1]

GRDC Incrop herbicide use [2]

APVMA registered products database [3]