by Katie Navarra
Bindweed has been spotted in farm fields within New York’s Capital Region. The hard to control weed has roots that can grow 30 feet deep. These long tap roots absorb water reserves deep in the ground, stealing it from shorter-rooted cash crops. Dormant bindweed seeds have a hard coating and can persist for 30, 40 or even 50 years.
“Freezing, thawing, and freezing and thawing abrades the surface of seed coats and that’s what allows seeds to germinate,” said Lynn M. Sosnoskie, Ph.D., assistant professor at Cornell AgriTech in Geneva, NY. “The seed coats have different thicknesses, which is why germination is sporadic rather than a flush.”
Sosnoskie shared outcomes from her research in California that can help farmers and scientists in New York begin to develop strategies for managing bindweed in Empire State fields. Her previous research provides a starting place; however, it can’t be assumed that control methods that worked elsewhere will necessarily apply to the species in New York.
The first step is proper identification. In New York there are three species referred to as bindweed: black bindweed, field bindweed and hedge bindweed.
Sosnoskie said black bindweed is the species New York farmers most often refer to as bindweed, but the summer annual is actually a part of the knotweed family. To distinguish between black bindweed and other varieties, look for a dry sheath around a stem formed by the cohesion of two or more stipules, called the ocrea. Black bindweed grows up to eight feet in length and has slender branching and delicate stems with arrow-shaped leaves. Flowers develop on racemes from axils of upper leaves.
True bindweed species include hedge and field bindweed. She explained that hedge bindweed has rhizomes and fibrous roots and root buds. The rooting forms from aerial shoots that can reach 10 feet deep or more. The leaves are larger than other species, with a pointed tip and deep-lobed base. The large flowers feature large bracts that cover the base of the tube.
Field bindweed grows vertically with lateral roots. The root buds form new crowns and tap roots, which can grow up to 30 feet deep. The plant has smaller leaves with rounded tips and flatter bases and smaller white to pink flowers with small bracts one inch below the tube.
Herbicides do not react equally in all species. Perennial plants have extensive root systems and herbicides can be diluted in that tissue. Perennial weeds can respond differently to applications due to the time of year, time of day and the corresponding differences in herbicide translocation. There are also inherent differences in sensitivity among bindweed species and populations.
“Some soil-applied herbicides have activity against perennial plants and not just the seedling stage,” she said. “Some pre-emergents are having an effect, such as Treflan, Matrix and Pre-Zeus. Allio will not control bindweed well but will damage grapes less than five years old.”
Glyphosate is currently the most effective management, according to Sosnoskie, but it’s not a one-and-done application. It must be applied two, three, even four times in some cases, to get control that lasts about two years. Other herbicides in the WSSA 4 and 9 classes have shown to be effective tools for suppression lasting greater than two years.
“We’re talking about suppression, not control. It’s important to understand that these tools aren’t once and done,” she said. “Site selection and effective pre-plant/in-crop herbicide should be used to start clean and stay clean.”
Cultural practices used in conjunction with herbicides may offer additional options. Bindweed is sensitive to light, so selecting cultivars for canopy development is important.
“New high density apple orchards are going to be problematic because the canopy is not there, so we need to figure out ways of suppressing bindweed until the canopies develop,” she said.
The best time to control bindweed is when it’s in its seedling stage, but that can be tricky. Bindweed root bud formation begins from two to 12 weeks. In research Sosnoskie conducted in California, she started to see survival at four weeks. But studies in New York and Washington have reported root bud formation as early as two weeks.
“Mechanical disturbance is likely to be important but needs to be applied frequently enough or in combination with other tools to avoid reestablishing populations,” she said.
Infrequent soil disruption can worsen germination rates by spreading root fragmentations between fields. Farms that engage in cultivation must be consistent and do it regularly, she advised. For cultivation to work, burial must be at least 10 inches deep, with 12 – 14 inches being preferable.
Cultivation done every two weeks requires about 21 – 28 cultivations to eradicate bindweed over a period of 18 – 24 months. When cultivation is done every three weeks it takes 18 – 22 cultivations to eradicate and almost 2.5 years.
“Disrupting dormancy and initiating root bud germination in fall when the plant wants to senesce utilizes weather/environment for control,” she concluded.