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Ministry of Agriculture, Food and Rural Affairs


Trade Names: Princep Nine-T, Simadex, Simazine 480

Registration status: This herbicide is registered for use in tender fruit orchards, except on plums and cherries as a residual herbicide under trees.

When to suspect injury: Injury from simazine may occur when simazine was used on fields before orchards were planted. Excessive rates on newly planted trees can also cause injury. Do not use on soils with less than 2% organic matter. Simazine can persist in soil for varying lengths of time depending on rate, weather and soil conditions (see below). If you notice symptoms of interveinal chlorosis, yellow to white margins and brown tips on older leaves,  ask for a herbicide history of the field and determine the soil pH and organic matter.

Herbicide Information:  Knowing how the herbicide works will help to determine the likelihood of injury from either direct application or drift.  Consider how the herbicide works in plants, behaves in soils and what symptoms are common in other plants. 

Chemical Family: S-triazine

Site of Action/WSSA Group:  Inhibitors of photosynthesis at photosystem II, (Site A) / Group 5

General Symptoms in Plants:

  • Interveinal chlorosis of leaves, with yellow leaf margins
  • Over time, leaves show general chlorosis and necrosis, and browning of leaf tips
  • Older leaves show more injury than new leaves

Symptoms in Tree Fruit:

  • Yellow to nearly white leaf margins, spreading to the mid-rib
  • Interveinal yellowing, eventually becoming necrotic
  • Symptoms often occur in early to mid-summer
  • Symptoms worsen during stressful weather (heat, drought)

Uptake and Translocation

  • Absorbed by roots; little or no foliar absorption
  • Translocated upwards in xylem, accumulating in apical meristem and leaves


  • Moderate residual
  • Half life: 30 days in fields, 60 days in ponds
  • Simazine is more persistent in high pH soils
  • Residues can injure crops 1 or more years after application

If you suspect herbicide injury, laboratory analyses of herbicide levels in plant tissue are necessary to confirm the presence of herbicides, although symptoms may be helpful in diagnosing which herbicides caused the problem.

Both damaged and healthy plant tissues should be analyzed, because comparison levels are not readily available for many herbicides. Contact your lab for instructions on which plant parts should be sampled, how to handle and ship the sample, and what costs are involved to ensure an accurate and timely diagnosis.

Simazine injury on peach leaves
Simazine injury on peach leavesSimazine injury on peach leaves Simazine injury on peach tree Simazine injury on cherryClick to enlarge.