Weed Control In Container Grown Chrysanthemums

By Andy Senesac
Weed Science Specialist, Cornell Cooperative Extension
Reprinted with permission from Greenhouse IPM Notes

In areas where fall bedding plants such as the chrysanthemum plants are grown, weeds may become a problem. Proper placement of containers is the key to successful weed control in the growing areas. To help reduce weed pressure and control weed populations in growing areas and mixes, we offer the following alternatives.

Growing media Most commercial growers are now using soilless media. Soil and, just as important, immature compost can be a source of weed seed. Starting the outdoor growing cycle with clean plants will prevent many weed problems.

Mulches Black polyethylene or the porous, woven plastic mats offer safe effective weed barriers. Mulches are best used in areas which are nearly level. However, weeds can become a problem even where mats are laid under pots, if holes in the mulch allow weeds to emerge through them.

Chemical Weed Control Weed control using chemicals offers further help to container growers without affecting plant growth, providing that reasonable precautions are followed. Following preparation of the weed-free growing area on which containers will be placed, treat the area with any one of the following:

Registered For Container & Field Grown Chrysanthemums:

  • Devrinol 10 G at 0.9 lbs/1000 sq. ft.
  • Pendulum 2G@2.3-4.6 lbs/1000 sq. ft. Pendulum 60 WDG 1.2-2.4 fl. oz/1000 sq. ft.
  • Ronstar 2G @ 2.25 lbs/1000 sq. ft.
  • Treflan 5G @ 1.8 lbs/1000 sq. ft.
  • XL 2G (Surflan + Balan) @ 4.6-6.9 lbs/1000 sq. ft.

FIELD GROWN ONLY - NOT REGISTERED FOR CONTAINER GROWN CHRYSANTHEMUMS

  • Pennant 7.8 Liquid 0.75-1.2 fl oz/1000 sq. ft. (not on LI)
  • Surflan 1.5-3 fl. oz/1000 sq. ft.

Preemergence Herbicides
When applied over the plants, all herbicides should be applied when leaves are dry. Following application, the herbicide should be watered in with one-half inch of water delivered from an overhead irrigation system. Beds under the container must be level and well drained to avoid herbicide accumulation in low areas.

Within the last several years, a class of selective postemergence herbicides has been registered that can be used over the top of actively growing chrysanthemums to control annual and perennial grasses. These herbicides, listed below, do not control broadleaf weeds or sedges.

Postemergence Herbicides for Use in Chrysanthemums to Control Grassy Weeds Only

  • Acclaim Extra @ 0.08-0.46 fl oz/1000 sq. ft.
  • Envoy @ 0.4-0.8 fl oz/1000 sq. ft.
  • Ornamec 170 @ 6 to 9 fl oz/1000 sq. ft.
  • Fusillade II @ 0.36 to 0.55 fl oz/1000 sq. ft.
  • Vantage @ 0.8 to 1.4 fl oz/1000 sq. ft.

Do not use any pre-emergence herbicides in greenhouses. Each herbicide is more effective against some weeds and less effective against others. Select one that is effective against weeds likely to be a problem for you.