Research Experiences With QuinStar 4L in Cranberries
In the past week or so some cranberry handlers have allowed use of QuinStar 4L as MRL export issues have been at least temporarily addressed to their satisfaction. Most importantly, allowed uses may vary by handler – be sure to follow the guidance provided by your specific handler.
Our research experiences with QuinStar 4L extend back to 2007. However, given MRL related use restrictions, there has been very limited commercial experience with the herbicide. Here, we provide a brief background on the product and a summary of some of our key research experiences.
QuinStar 4L background
Quinclorac, the active ingredient in QuinStar 4L, is an auxin mimic herbicide in the same mode of action as herbicides such as 2,4-D and clopyralid (Stinger). Quinclorac’s strength as an herbicide relative to others in the mode of action is largely a result of two aspects: it’s taken up by both shoots and roots, allowing for greater activity on perennial weeds, and it’s persistent in soil, allowing for longer residual weed control. It’s most active on broadleaf weeds but also can suppress some grasses. In Wisconsin, it has been very effective in controlling dodder when applied soon after emergence.
QuinStar 4L research experiences
There are a few key observations worth sharing from our small plot experiences with QuinStar 4L:
- Applications to newly emerged but small weeds provides better and more immediate control than applications to large, well-established weeds. Very importantly, applications to perennial weeds may not show any symptoms or signs of control for several weeks after application, and maximum control may not be evident for at least 3 to 6 months and sometimes not until the next season – be patient!
- Given that control of newly emerged, young weeds was greater than applications to established weeds, the vast majority of our research experiences are based on pre-bloom applications. With that said, in our research we have not seen crop injury from pre- or post-bloom applications. We did not make applications during bloom and wouldn’t suggest it.
- Herbicide persistence can be both positive and negative. On the positive side, the persistence allows for long term weed control. On the negative side, persistence can lead to herbicide residues in fruit. Be sure to carefully follow the 60-day pre-harvest interval and labeled rates.
- Like with any herbicide, control varies by weed species. Across our research studies we observed good to excellent control of yellow loosestrife, dodder, slender-leaved goldenrod, sticktights and ditch stonecrop. We observed about 50% control of marsh and northern St. Johnsworts. Control of some species, such as dewberry and the clovers, was more variable, ranging from mediocre to very good, but seemed to be most related to application timing where earlier was better. In general, late-season perennial weeds are more difficult to control not only because they’re more established but also because many species such as dewberry develop thick, waxy leaf surfaces as they become hardened off by heat and other plant stresses.
- QuinStar 4L requires an adjuvant to optimize weed control. In our studies we used non-ionic surfactant to enhance weed control efficacy while reducing crop injury risk as compared to crop oil concentrates that we know can be injurious to cranberries, particularly in fruit set application timings.
- In our early research, from which most of these observations are based, we didn’t fully realize how persistent the control would be with QuinStar 4L. Therefore, our research observations include the season in which the herbicide was applied, but our limited observations from commercial applications in Wisconsin and elsewhere suggest that oftentimes weed control wasn’t maximized until the following growing season. For example, one grower applied QuinStar 4L once to established dodder and had minimal control in that growing season, but very effective control in the following season. Again, be patient!