Weed Control - Bittercress
Wednesday, 21 December 2011 14:12
Bittercress has been a problem in some high tunnels and greenhouses (any bare ground) as it continues to grow during warm temperatures like we have had recently. Bittercress (Cardamine hirsuta L.) is a winter annual weed in the Brassicaceae (Cruciferae) or Mustard Family. Stems can be 3-9 inches long, and as you can see in the photos (UMass Weed Herbarium), the leaves are mostly on the lower portion of the stem in a basal rosette. Flowers are small and white. Small round capsules develop at the ends of each branch. The persistence of bittercress, is primarily due to its’ seed dispersal mechanism. Bittercress capsules explode, sending seeds long distances.
Bittercress germinates in the fall and grows during warm weather. Optimal temperatures for growth are between 45 and 85°F, otherwise it will remain dormant during the winter. It will resume growth and produce seed in the spring and die as temperatures increase in late spring and early summer. This weed quickly invades open soil especially where there is good soil moisture and shady spots. The seed can stick to the soil on the outside of containers or shoes and be moved throughout a greenhouse range. The seed can also be easily carried in irrigation water. Seeds do not have a dormancy period and may germinate immediately. Combined with the short life cycle (6 weeks), a heavy weed population can occur rather quickly.
Management: There are no preemergence herbicides registered for greenhouse use. Options include non-selective postemergence herbicides, hand-weeding and physical barriers.
Vegetables or Food Crop: If a vegetable or food crop is present, then hand-weed often when plants are small, before flowering.
Options for empty greenhouse or high tunnel (no crop present)
Herbicides for empty greenhouses include materials containing glyphosate such as Roundup, Touchdown Pro and many different generic products. Glyphosate is a non-selective, systemic, postemergence herbicides which does not have residual control or pre-emergence activity. Bittercress must be actively growing for these herbicides to work.
Other materials include non-selective contact, postemergence herbicides such as pelargonic acid (Scythe) (slow activity during cool temperatures).
Organic options include non-selective, contact herbicides: clove oil (Matratec) and acetic acid (Weed Pharm).
Physical barriers: Another option is to put weed fiber-cloth down on the floor and leave it there until you are ready to plant (high tunnels). This will suppress any more weed growth this winter. If any seeds germinate where there are bare areas (edges etc), spot treat with herbicide or hand weed before plants go to seed. Suppression may be possible with just the greenhouse weed, fiber cloth.
Off-season tip
To exhaust the seed source in beds, for greenhouses or high tunnels that will be empty for an extended period of time, shallow rototill (1/4" or so) to bring up seeds. As the seeds germinate, treat the small plants with herbicide before they flower and seed. The herbicide must be applied as soon as possible and reapplied as needed. Over time, this will reduce the bittercress population by exhausting the weed seed bank.
Photos: UMass Extension Weed Herbarium
Tina Smith, UMass Extension
with input from Randy Prostak, Weed Specialist for ornamental crops, UMass Extension and Rich Bonanno, Weed Specialist for vegetable crops, UMass Extension
