Managing bindweed in perennial crops like apples and blueberries is challenging. This has become clear even after only working as the weed science extension educator for four months.
Colloquially, “bindweed,” can refer to several different species. Annual morningglories (Ipomoea spp.), annual wild buckwheat (Fallopia convolvulus), and perennial hedge (Calystegia sepium) and field (Convolvulus arvensis) bindweed can all be called “bindweed”. See this excellent site to help distinguish between these different species. I prefer to only refer to the perennial bindweeds as true bindweeds (C. sepium and C. arvensis). These species are both perennial and spread extensively from underground growth, which makes them particularly difficult to manage.
Quinclorac used as a pre-emergent herbicide is a relatively new option to control bindweeds in blueberries. Herbicides can be classified into two categories depending on whether their mode of action kills weeds before they have emerged (pre-emergent) or after they are actively growing aboveground (post-emergent). Quinclorac can be used both ways. It is absorbed through the roots, and to a lesser extent the leaves, of germinating seeds and seedlings, killing weeds both before and after they have emerged. The exact mode of action of quinclorac, which is sold commercially as Quinstar 4L, is still unknown, but it is a group 4 auxin mimic that prevents cell wall synthesis and produces reactive oxygen species that selectively kills plants1.
Several years ago, Dr. Marcelo Moretti and Dr. Edward Peachey, two weed scientists in Oregon, began research looking for more bindweed control options for blueberry growers on the West Coast. They knew that quinclorac could effectively control bindweed with a pre-emergent application, but they were not sure if it was safe to use pre-emergent in blueberries2 . Over six years of research, they established not only that pre-emergent use of quinclorac in blueberries was safe, but that it provided more effective control of bindweed than post-emergent use3. As a result, the manufacturer updated the label in 2018. Now, growers can use a pre-emergent application of quinclorac, followed by a second, post-emergent, application 30 days later as long as there are at least 30 days before harvest, to control their bindweed.
However, just because it is on the label does not mean everyone has immediately started using quinclorac this way. Many growers may not know this use is now an option. Quinclorac is still associated with post-emergent use, as it was only used this way prior to its recent label change. Plus, the research in Oregon was done on clay and loamy soil. We are not sure what the optimal rate is for blueberries grown on sandy soils typical of the Northeast. Generous funding from the Massachusetts Fruit Grower Association has allowed Matthew Bley and I to study quinclorac’s effectiveness in controlling the bindweed in blueberries at UMass’s Cold Spring Orchard in Belchertown, MA.
Applying pre-emergent quinclorac is best done in the spring, after dormancy but before budbreak. Despite unpredictable weather this spring, Bley and I managed to find what we hope is the perfect window during the last week of March. The ground had thawed after that weekend’s ice storm and we got 1.3 inches of rain over three days after applying, which should help activate the quinclorac. We are trialing two different rates, a low rate of 6.3 fl oz per acre (0.19 lb ai/A) and a high rate of 12.6 fl oz per acre (0.375 lb ai/A). We also applied a crop oil concentrate to help the quinclorac remain in the soil, and another pre-emergent herbicide called Chateau EZ (a new formulation of Chateau SW) to target primarily annual broadleaf weeds.
Our research this summer will also investigate whether changing the soil’s microbial community and reducing the rate of nitrification can affect the types of weeds in the blueberry field. The novel use of nitrification inhibitors in perennial systems will lay the groundwork for future research. We will keep you updated throughout the season and are eager to share our findings at the Cold Spring Orchard summer field day.
In the meantime, here’s a list of other pre-emergent herbicides for blueberry fields compiled by Dr. Thierry Besancon from New Jersey. This list is from 2022 and the herbicide options may not exactly match herbicides labeled in Massachusetts. Always read and follow label instructions when using pesticides—it’s the law.
1Fipke MV and Vidal RA (2016) Integrative theory of the mode of action of quinclorac. Planta Daninha 34:393-402
2Enloe SF, Nissen SJ, and Westra P (1999) Absorption, fate, and soil activity of quinclorac in field bindweed (Convolvulus arvensis). Weed Sci 47:136-142
3Moretti ML and Peachey RE (2022) Field bindweed control with quinclorac in highbush blueberry. Weed Technol 36:197-201