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Phoma macrostoma (strain 94-44B)

Herbicides whose active ingredient is Phoma macrostoma kill Canada thistle (Cirsium arvense)
Photo: Mykhailo Pavlenko
Canada thistle (Cirsium arvense)

The information below is intended only as a guide. Always read product labels carefully.

Product description

This herbicide, whose active ingredient is Phoma macrostoma (strain 94-44B), is created from a parasitic fungus naturally found in Canada thistle (Cirsium arvense).

This bioherbicide is used in lawns to eliminate or repress broadleaved weeds.

This product is usually sold in ready-to-use granular form.

Target plants

Herbicides whose active ingredient is Phoma macrostoma (strain 94-44B) may be used to control various weeds such as:

  • Common dandelion (Taraxacum officinale)
  • Canada thistle (Cirsium arvense)
  • Common chickweed (Stellaria media)
  • Common plantain (Plantago major)
  • Common ragweed (Ambrosia artemisiifolia)

Caution: This herbicide kills white clover (Trifolium repens).

NB: The product label lists the plants on which the pesticide may be used, along with the target organisms. 

How it works

The Phoma macrostoma (strain 94-44B) causes broadleaved plants to whiten. Without chlorophyll, the plants die. When applied to the lawn before weed emergence, the fungus causes the emerging thistles of sensitive species to come up white. This product does not harm grass.


Localized applications are possible on well-established or newly seeded lawns. You can also spread the product before or after weed germination on a lawn.

Treatment can be done any time from the spring to the fall. For best results, however, apply when the average daytime temperature is between 15 and 30°C and the soil is damp. There is no need to water the lawn following treatment, but it should be done if there is no rain in the 24 to 72 hours following application, especially if the ground is dry when spreading. We recommend mowing the lawn before applying the product.

A single pre-emergent application can control the thistles of several undesirable species. Well-established plants may require two or three treatments over the course of a month.


This product must not come into contact with ornamental plants, fruits and vegetables, as it can damage several broadleaved plant species. In case of contact, rinse with water.

Avoid all contact of the product with the eyes and carefully wash your hands with soap and water after applying the treatment. We also recommend washing contaminated clothes before wearing them again.

Do not apply this product close to a body of water, watercourse or wetland. Moreover, avoid contaminating the water of these habitats and sewers by disposing of the excess pesticide or rinsing the application equipment there.

Keep this product out of the reach of children.

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