Diagnosing contact herbicide and spray additive damage in canola

This includes contact herbicides from a range of chemical groups that require uniform spray coverage to be fully effective. Symptoms appear within hours (Group L), or 1-2 days (Group G) of application.

Sprayed leaves shrivel rapidly
Affinity (Group G) sprayed plants have necrotic droplet size lesions that may have a purple margin
Group L Bipyridyls chemical name Example trade name
Diquat Reglone
Paraquat Gramoxone
Diquat+paraquat SpraySeed
Group G Aryl triazalinone chemical name Example trade name
Carfentrazone

Affinity

Hammer
Group G Diphenyl ethers chemical name Example trade name
Oxyfluorfen Goal

What to look for

    Paddock

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

    Plant

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

What else could it be

Condition Similarities Differences
Diagnosing group F herbicide damage in canola Pale leaf blotches and streaks on sprayed leaves Damaged caused by group F herbicides fade without causing any lesions

Where did it come from?

  • Serious damage is generally caused by direct spraying. Contact herbicide spots may be caused by spray drift, but plants will generally recover.
  • 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.
  • Bipyridl herbicides have some movement within a plant if sprayed at night, and consequently cause more damage than when sprayed in daylight

Topics

Page last updated: Wednesday, 12 July 2017 - 12:18pm