How to identify and manage hairy bittercress in nurseries and greenhouses – Part 2

Managing hairy bittercress (Cardamine hirsuta L.) early in container production can help growers improve their ornamental production.

Basal leaves of hairy bittercress in a dense rosette form.
Basal leaves of hairy bittercress in a dense rosette form. Photo by Debalina Saha, MSU Horticulture.

Hairy bittercress is one of the most problematic weed species in nursery and greenhouse container production. It is typically a fall germinating weed but can grow in the greenhouse throughout the year and needs to be controlled for successful ornamental production. In this second part of this Michigan State University Extension article series, we will discuss how to control hairy bittercress in nursery and greenhouse container production.

Non-chemical control

Prevention is the first step to control hairy bittercress in ornamental crop production. It is important to use weed-free substrates, inspect plant material and containers for weed infestations, and maintain healthy plant growth that can compete with or prevent weed establishment. Due to its extensive seed spread via forcible dispersal, it is important to control the plants at early stages by regularly scouting containers and facility floors and perimeters.

Coarse textured mulches can be applied to nursery plants at a depth of 2 inches in order to avoid germination of weed in soil. Hand weeding or using a weeding tool is primary means of pulling or digging out young hairy bittercress plants before they reach the reproductive stage. Regular mowing also helps reduce seed production but will not kill the plant.

Chemical control

Non-chemical weed control methods alone may not be very effective if there is a severe infestation of hairy bittercress. In that case, a herbicide application should be combined with the non-chemical methods.

There are two herbicide types that can be used to control hairy bittercress: preemergence and postemergence. Preemergence herbicides are applied before weed seed germination takes place and prevent successful emergence. Postemergence herbicides are applied to the foliage after weed emergence when plants are young and actively growing.

Preemergence herbicides

Hairy bittercress can be effectively controlled by application of preemergence herbicides. Growers must ensure proper sanitation and weeds seed exclusion strategies and the containers and substrates must be free of weed infestation before application of herbicides.

Preemergence herbicides effective in controlling hairy bittercress include oxadiazon (Ronstar) and isoxaben (Gallery), oryzalin (Surflan), and isoxaben plus trifluralin (Snapshot). The preemergence herbicide indaziflam (Marengo) is labeled for application on greenhouse floors. The greenhouse or structure must be empty during the application; ornamental plants can be returned 24 hours post treatment.

Another herbicide, flumioxazin (SureGuard) can also be used for treating empty greenhouse or structure floors, according to Marble et al., 2014. Growers may have to combine the application of preemergence herbicides with hand weeding for effective control of hairy bittercress.

Postemergence herbicides

Postemergence herbicides need to be applied when hairy bittercress is young and actively growing, before reaching flowering and seeding stage. There are several types of postemergence herbicides (both contact and systemic) available to control hairy bittercress in outdoor nursery containers, which includes glyphosate (RoundUp), diquat (Reward), glufosinate (Finale) and pelargonic acid (Scythe). Proper coverage with contact herbicides such as diquat and pelargonic acid is necessary for effective control, according to Marble et al., 2014.

Diquat (Reward), glufosinate (Finale) and pelargonic acid (Scythe) are labeled for use inside the greenhouse or enclosed structure. Always try to avoid direct contact of herbicides with the ornamental plants to prevent herbicide injury both inside and outside greenhouse conditions. Also, it is recommended to consult manufacturer’s label on herbicide and follow all precautions during the use of any herbicide for effective weed control.

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