Diagnosing contact herbicide damage in cereals

This category includes contact herbicides from a range of chemical groups that require uniform spray coverage to be fully effective.

What to look for

Widespread plant bleaching and limpness.
Wind drift damage is worst on paddock edges, temperature inversion drift occurs in low lying areas.

The pattern of damage reflects spray coverage and may be worse on one side of the plant. Plants die or recover with fresh new shoots appearing.
Numerous pale necrotic spots sometimes with a brown edge or streaks on the leaves and stems and occasional leaf tip death.
More serious damage includes leaf wilting, interveinal chlorosis, marginal leaf burn and leaf death.
Severely damaged plants shrivel up within four days of application.

Spraying herbicide

Temperature

Serious damage is generally caused by direct spraying. Contact herbicide spots may be caused by spray drift, but plants will generally recover. Damage declines with distance from intended spray area and spotting will be worse on the side of plants facing the source of the spray.
Group G damage symptoms are greater when spraying occurs under humid, high temperature, high moisture, dewy and high sunlight conditions. Plant symptoms will also be greater where adjuvants such as oils are used. There has been no reported yield loss associated with these symptoms.
Plants stressed by frost are more susceptible to damage by bromoxynil.
Bipyridl herbicides have some movement within a plant if sprayed at night, and consequently cause more damage than when sprayed in daylight.

There are no treatment options, plants either die or completely recover. As a precaution, spray when the risk of drift is low or when environmental conditions are safe.

HerbiGuide [1]