Nursery - Weed Management in Container Nurseries

The following is some information on weed control in container nurseries from a presentation by Dr. Stephen Hart at Rutgers.

The weeds that are found in container nurseries are different than in field grown nurseries. Major weed species are bittercress, Oxalis, and common groundsel. These are normally winter annuals but due to the use of irrigation and covered houses, the growth cycle is year round. These and other weeds of containers can have multiple generations per year. Bittercress and oxalis have forceful dehiscence, that is the pods expel the seeds when mature. Grounsel produces fluffy seeds that are easily wind borne.

The first key to weed control in containers is sanitation. You should start out with no seed bank. Because containers are placed on landscape fabric with or without gravel, there should be complete vegetation control. The goal is to prevent the occurrence of weed seeds in containers. Weeds can come in on infested liners, can blow in from surrounding areas, or can come from media that is infested with seed. All media and containers should be stored in a manner to avoid any contamination with weed seeds. Do not reuse containers unless thoroughly cleaned and disinfested. Cover media piles and do not let any stray weeds grow on media piles. Use non-selective herbicide spot sprays to kill any weeds that come up in surrounding nursery areas - roads, between blocks, alleyways, along the sides of overwintering houses, around potting facilities, and other similar areas.

For container weed control, timing of herbicide applications is critical. Scout containers and eliminate any infested with perennial weeds. Do no attempt to save any containers that have weeds such as nutsedge or mugwort. Before applying herbicides, hand weed any annuals that you find. Irrigate prior to herbicide application to settle the soil. Apply granular herbicides after foliage had dried. Irrigate immediately after herbicides have been applied to container plants to remove any herbicides that is stuck on foliage.

Herbicides labelled for containers include pendimethalin (Pendulum), prodiamine (Factor), trifluralin (Treflan), oryazalin (Surflan), isoxaben (Gallery), oxadiozon (Ronstar), and flumioxazon (Broadstar). Combination products for use in containers include Snapshot (isoxaben plus trifluralin), OH2 (oxyfluorfen + pendimethalin), Rout (oxyfluorfen + oryazalin), and Showcase (isoxaben + oxyfluorfen). Most are in granular formulation.

Herbicides such as Rout, OH2, Showcase and Ronstar are very effective for those container plants they are labelled on. The also will provide some control of existing liverworts and some emerged seedling broadleaf weeds. Unfortunately they have a relatively narrow label (the plants they can be used on). Granular formulations of Snapshot, Treflan, and Pendulum have very wide labels and good crop safety. Factor and Gallery are two other herbicides with wide container crop labels. Broadstar is also labeled on some plants and is very effective. You may consider applying sequential applications of these herbicides at reduced rates.

Showcase, Rout, and OH2 are the most effective on bittercress; Rout and Broadstar are most effective on groundsel, and Snapshot, Showcase, Rout, and Broadstar are the most effective on Oxalis.

Summarized by Gordon Johnson, Extension Horticulture Agent, UD, Kent County