This past spring and summer, a trial was conducted to compare the efficacy of most commonly used preemergence herbicides. While the list of herbicides used does not represent every product available, it does provide comparative information for most herbicides and how they should perform 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
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| Granular preemergence herbicides were evaluated for control of common container weeds. Each species was evaluated separately (different color tags). |
One gallon containers were filled with 100% coarse Douglas fir bark on May 6, 2004. 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 were grown under 47% shade). All plants were irrigated overhead with approximately 1/2 inch water/day split in two equal cycles.
Herbicides were applied on May 17, 2004. Seed of each weed species were applied the following day. Herbicides were 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 |
| Regal Star | oxadiazon+prodiamine | 200 |
| Regal Kade | prodiamine | 200 |
| OH2 | pendimethalin+oxyfluorfen | 100 |
| Kansel + | oxadiazon+pendimethalin | 100 |
| Ronstar G | oxadiazon | 200 |
| Snapshot | trifluralin+isoxaben | 200 |
| Control |
Rates used represent the maximum labeled rate for each product. Some have questioned why I use 200 lbs of one product, but only 100 pounds of another. Is that fair? These products are formulated with various percentages of active ingredient. Based on the percent active ingredient, the manufacturer decides at which rate is can be safely applied to container crops. The only fair way to compare these products is to evaluate them at their highest recommended rate.
For those interested in statistical details, containers were arranged in completely randomized design with 8 single container replications. 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.
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