Keeping Bindweed in Check; Lynn Sosnoskie Research

Help may be on the horizon for tomato growers wrestling with field bindweed, the noxious plant with the pretty little white flowers that will not go away, no matter what you do.

Management of this weed is never-ending because it regenerates quickly and easily from a vast root structure, and also sets seeds that remain viable for as long as 50 years.

University of California researchers are studying how much more effective the best herbicides can be on field bindweed when they are applied in the right place in the soil, or at the best time of day.

Growers look on the white flowers with chagrin, knowing the plants are stealing water and nutrients from their crops. (photo: Bob Johnson)
Growers look on the white flowers with chagrin, knowing the plants are stealing water and nutrients from their crops. (photo: Bob Johnson)

“We wanted to look at incorporating Treflan four inches deep,” said Lynn Sosnoskie, UC Davis assistant project scientist. “Much of the biomass of the roots goes down to 18 inches, but we treat it by incorporating at only two or three inches.” Sosnoskie works in the Department of Plant Sciences, UC Davis.

In another set of plots a few yards away from the Treflan trial on the Davis campus, researchers are hoping to confirm that post-emergent materials are more effective when applied near the middle of the day.

“These studies have been done in the Midwest and Southeast on annual weeds,” Sosnoskie said. “I wanted to do a study on a perennial weed under California conditions.”

Lynn Sosnoskie, University of California, Davis, assistant project scientist, checks out an herbicide applicator rigged to put the material four inches below the surface. (photo: Bob Johnson)
Lynn Sosnoskie, University of California, Davis, assistant project scientist, checks out an herbicide applicator rigged to put the material four inches below the surface. (photo: Bob Johnson)

She made her remarks while the growers and researchers at the 60th Annual UC Weed Day on the Davis campus looked over the trial plots, and at an applicator that had been modified to put Treflan four inches below the surface.

The only time to think in terms of eradicating bindweed is when the seedlings are young, still small, and without an extensive root structure, she said.

“Although bindweed seedlings are relatively easy to manage using physical and chemical control strategies, established plants with extensive root systems are relatively tolerant to most management practices,” Sosnoskie said.

Once established, however, bindweed can cause extensive damage to crops and harvesting activities unless it is controlled vigilantly.

“If field bindweed is allowed to compete with tomatoes during the period of canopy establishment, up to eight weeks after transplanting, it can significantly reduce both fruit numbers and quality,” Sosnoskie said. “Furthermore, field bindweed vines can become physically entwined with tomato plants, which, in turn, can reduce harvest efficiency.”

In a study last year, placing the herbicide Treflan deeper into the soil helped to control bindweed, but this application was done too close to planting and it damaged the tomato plants.

Part of the challenge in controlling this most persistent of perennial weeds is that it can easily regenerate from roots that run so deep and are so large that it is all but impossible to get enough material into them to achieve a lethal dose.

It may be possible, however, to slow the plant down a little more with herbicides that are taken up by more of the root structure because they are applied deeper in the soil.

Campus researchers rigged a homemade contraption with hoses that apply the material at the points of cultivator blades that cut into the soil at a depth of four inches.

Field shows how extensively field bindweed can spread. (photo: Bob Johnson)
Field shows how extensively field bindweed can spread. (photo: Bob Johnson)

Because it is unrealistic to think in terms of eradicating bindweed, most growers try to burn it down before planting in order to give their tomatoes or other crop a head start.

In a second trial in the UC Davis test fields, researchers are hoping to confirm that materials like glyphosate and glufosinate are more effective at this burndown when they are applied in the middle of the day.

“This is a study to look at the timing of post-emergence applications on bindweed,” Sosnoskie said. “This is looking at how the time of day of the application affects the weed control.”

In that trial, researchers are observing different application times during the day for the most widely used post-emergence materials on bindweed — glyphosate, glufosinate, rimsulfuron, salflufenacil and paraquat.

Each of these materials was applied an hour before and after both sunrise and sunset, and in the middle of the day.

“There have been studies showing glyphosate and glufosinate can perform differently depending on the time of day; these studies have shown they are more effective when applied near the middle of the day,” Sosnoskie said.

The time of day could make a difference in temperature and humidity, the presence or absence of dew, the physiological activity of the plants depending on the sunlight, and even the angle of the leaves at the time of application.

Although these studies have been done before, this is the first time they have been done on bindweed, and the first time they have been done in California.

Once the weed has become mature and established, however, chances are it will have to be treated regularly because it can keep coming back from the roots, or from seeds that can remain viable in the ground for decades.

Farmers have been trying, largely without success, to rid themselves of this weed since ancient times.

The Greeks had a term for bindweed that means “circling plant,” while the Roman term translates roughly into “large worm that wraps itself in vines.”

(Article written by Bob Johnson, a reporter in Davis. He may be contacted at bjohn11135@aol.com. Article reprinted from Ag Alert, California Farm Bureau Federation.)

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