NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

July 1, 1999

Nightshade Concerns Increase Among Region's Dry Bean Growers

The most recent survey involving a group of the region's dry edible bean producers indicates that concerns about eastern black nightshade are increasing significantly. A weed scientist at North Dakota State University says several factors have been contributing to the nightshade problem, but he notes that this year a newly registered herbicide offers effective control and more flexibility for crop rotation planning.

The annual dry bean grower survey seeks responses from the Northarvest Bean Growers Association, whose membership comprises producers in Minnesota and North Dakota. In 1998, 29 percent of the Northarvest respondents, representing 36 percent of the dry bean acreage covered by the survey, said nightshade was their worst weed problem. By comparison, 14 percent of the 1997 respondents, representing 18 percent of that year's survey acreage, said nightshade was their worst weed problem.

Despite that significant one-year change in survey responses, the nightshade problem in dry beans has been building for years, says Richard Zollinger, extension weed specialist at NDSU. The "fuel" propelling this increase is precipitation.

"Nightshade loves rain," Zollinger says. "Rain can trigger recurring flushes of nightshade seed germination throughout the growing season."

And as its name implies, nightshade also flourishes without the benefit of direct sunlight, so a dry bean canopy provides little competition against the weed's mid and late-season development. Prior to this year, many dry bean producers battled nightshade by relying on cultivation and high rates of herbicide.

But preplant incorporated (PPI) herbicides such as trifluralin or Sonalan can't control subsequent flushes of nightshade brought on by rainfall, Zollinger explains. And prior to this year, the only effective postemergence herbicide labeled for broadleaf weeds in dry beans, Pursuit, carried with it a 40-month restriction for planting sugarbeets.

"Basically, that restriction has meant that a sugarbeet grower who grows dry beans can not use Pursuit," Zollinger says.

But based on responses to the 1998 dry bean survey, it appears that some producers who grow both dry beans and sugarbeets have developed new weed-management strategies. A quarter of those responding to the 1998 survey said they applied Pursuit postemergence to their dry bean fields. In the 1997 survey, only 10 percent of the respondents said they used Pursuit.

"What this tells me is that a sugarbeet grower who has nightshade may tend not to rotate to sugarbeets because nightshade is getting to be such a bad problem," Zollinger says.

This year, reaching that type of a decision may be unnecessary. Zollinger says the Environmental Protection Agency has granted a section 18 exemption for Raptor on dry beans. Raptor is similar to Pursuit in its effectiveness on nightshade, but it has a shorter crop-rotation restriction to sugarbeets—only 18 months for soils with a pH greater than 6.2 and 26 months for soils with a pH of less than 6.2.

"Raptor is very effective on nightshade," Zollinger concludes. "We got the section 18 based on the nightshade infestation."

The 1998 dry bean growers survey occurred during Northarvest Bean Day, held last Jan. 22, says Art Lamey, extension plant pathologist at NDSU. Lamey helps administer the survey and compile the data. The 1998 dry bean survey generated 176 usable responses, 15 percent fewer than in 1997. The 1998 survey responses represent 96,719 acres, slightly more than 10 percent of the total Northarvest acreage (940,000). Prior to 1997, Northarvest growers received the surveys by mail. Complete results from the 1998 survey will be published later this year.

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Source: Richard Zollinger (701) 231-8157

Editor: Dean Hulse (701) 231-6136