Landscape
And
Nursery
Dialog
Mary Ann Rose
Commercial Landscape
& Nursery Specialist
The Ohio State UniversityFebruary, 1998
The Latest NEWSS in Weed Control Research.
Keywords: herbicides, new research, weed control, nursery, landscape
T he first week in January I attended the Northeastern Weed Science Society (NEWSS) meetings in Washington D.C., and had an opportunity to learn from the leading experts in nursery and landscape weed control. I also had the opportunity to take in the sights of Washington, D.C! What follows are research findings that I think are significant for Ohio nursery and landscape professionals.
Bittercress Control. Bittercress is a small, white-flowered mustard that is prolific in seed production. I had to laugh once when a nurseryman placed the weed flat on a xerox machine, and faxed me the copy he made! It wasnāt hard to identify this annoying little winter annual that infests container ornamentals and polyhouses - even a faxed, xerox reproduction of one! Once it becomes established in gravel floors itās nearly impossible to keep the weed out of containers because it squirts its seeds almost 4 feet.
One experiment presented at the conference examined long-term control of bittercress in gravel floors using a number of preemergence herbicides. The most promising herbicides appeared to be Factor (prodiamine) and Goal EC formulation (oxyfluorfen) for long term control. Pendulum (pendimethalin), oxyfluorfen granules, and a combination of oxyfluorfen + oryzalin (Goal + Surflan) gave intermediate control of bittercress. In most cases, the rates used in the study were higher than label rates. We can hope to see label changes for this use soon. This study also provides some guidance for choosing products to keep bittercress out of containers. Factor and Pendulum are labeled for many container crops, whereas Goal EC is labeled for conifers only. Goal (oxyfluorfen) in granular form is contained in OH-2, Rout, and Regal O-O.
Another herbicide that had good control for bittercress in this study was Dimension (dithiopyr), which does not currently have a nursery label. However, ornamental landscape use recently has been added to its label. This herbicide has been an excellent product for the control of crabgrass in turf - both preemergence and early postemergence. The sprayable formulations allow the use as directed sprays around many ornamentals. Iāve been told that granular formulations will be soon be available that allow use in ornamental beds.
Other Future Herbicides. I also presented my own work with a new chemical, thiazopyr, at the conference. This chemical is not yet available for ornamentals, but appears to have excellent potential. In my study, the sprayable EC formulation of this chemical controlled grassy weeds in containers for four months at 0.5 lb./aia. The only other product that provided the same degree of control was the sprayable WDG formulation of Factor (prodiamine) at 1 lb./aia. To my surprise, both of these chemicals also controlled broadleaf weeds for about 2 months, - I had not expected either product to do much for broadleaf weed problems.
An interesting observation from the experiment was longer-term control of grassy weeds with sprayable formulations compared to granular formulations. Comparing notes with other scientists, many said theyāve also observed better control from sprayable v. granular formulations of herbicides. Nurserymen who are really struggling to gain weed control across the nursery may want to take note of this. Most container nurseries in Ohio are using granular products because of the ease of application, but the potentially superior control provided by sprayable formulations may be worth the effort of making spray applications.
New Roundup Pro, problem for conifers.
Another presentation dealt with potential injury to conifers from the newer formulation of glyphosate (Roundup Pro) compared to the original Roundup (no longer available). Using the original formulation, conifer and Christmas tree growers have, for years, made semi-directed sprays to conifers in the dormant season (early spring or fall) -without risk of injury. The new formulation, Roundup Pro, contains an improved surfactant that increases foliar absorption. The study showed that Roundup Pro did cause significantly greater injury than Roundup. The greatest risk was to small trees (less than 2 feet) where it was impossible to prevent the spray from reaching the upper branches. Several other currently available formulations of glyphosate were tested in this experiment and did not cause the injury seen with Roundup Pro: Glyfos and Accord appear to be a good choice for conifer growers. Accord was used with Entry II surfactant, a necessary addition since this product contains no surfactant.
One Last Thing
An announcement of a new weed control bulletin seems an appropriate conclusion for this article. Bulletin 867, 'Controlling Weeds in Nursery and Landscape Plantings', should be available in February, 1998 through your county extension office. This publication has been a joint effort between Penn State and Ohio State. As I write this article, it is being printed, so you may have to nudge your county agent to order it for you.
