Comparison of granular preemergence herbicides for controlling container weeds

This past summer a trial was conducted to compare the efficacy of several commonly used preemergence herbicides. While the list of herbicides used does not represent every product available, it does provide comparative information on which herbicides might perform better in Oregon container nurseries.

Results in other nurseries and growing conditions may vary from those reported here. It is the author's opinion that cultural practices used in nursery production greatly affect weed vigor and herbicide efficacy. The exact cultural conditions used in this trial are listed below so they can be compared to those at your nursery and taken into account.

Methods

Granular preemergence herbicides were evaluated for control of common container weeds. Each species was evaluated separately (different color tags).
These experiments were designed to test efficacy of several granular preemergence herbicides for control of common container weeds including: bittercress, northern willowherb (a.k.a. fireweed), pearlwort, liverwort, prostrate spurge, and common groundsel. Each weed species was evaluated separately. Northern willowherb (NWH) containers were inoculated from natural seed infestations. Liverwort were inoculated by placing containers immediately next to another container infested with liverwort (spore inoculation and splashing by gemmae). All other species were inoculated by placing 20 weed seed on the container surface (seed were collected and counted earlier).

One gallon containers were filled with 100% coarse Douglas fir bark on July 2, 2003. Bark was amended with 1.5 lbs/yd3 of Micromax and 12 lbs/yd3 Osmocote 18-6-12. Containers were placed on a gravel container pad in full sun (bittercress and NWH were grown under 47% shade). All plants were irrigated overhead with approximately 1/2 inch water/day split in two equal cycles. Approximately one week after potting and herbicide application, containers were over-seeded with 20 seeds from one weed species. Herbicides applied at the following rates:

Herbicide Active ingredients Rate (lb product/acre)
Rout oryzalin+oxyfluorfen
100
Broadstar flumioxazin
150
Regal O-O oxadiazon+oxyfluorfen
100
OH2 pendimethalin+oxyfluorfen
100
Snapshot trifluralin+isoxaben
200
Control    

Rates used represent the maximum labeled rate for each product.

For those interested in statistical details, containers were arranged in completely randomized design with 4 replications of 4 single container subsamples each. Weed species were randomized separately.

Results and Discussion

Results for each weed species are separated below. Click on the image or the weed name to see herbicide trial results. Click on the words 'Identify this weed' to see additional photos of each plant.

Bittercress (Cardamine hirsuta) Identify this weed
Northern willowherb (Epilobium ciliatum) Identify this weed
Liverwort (Marchantia polymorpha) Identify this weed
Prostrate spurge (Chamaesyce maculata) Identify this weed
Pearlwort (Sagina procumbens) Identify this weed
Common groundsel (Senecio vulgaris) Identify this weed

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