Venice mallow control challenges prompt herbicide study in dry beans

Casper – With Wyoming falling in the top 10 for a number of production characteristics related to dry beans, controlling weeds and pests in the crop is important to producers. However, challenges with weeds, including Venice mallow, are often hard to address, as pesticide labels frequently don’t include the weed.

Jenna Meeks, a University of Wyoming (UW) researcher, commented, “Venice mallow, as with most weed species, came from another country where people thought it was pretty. Here it is a nuisance.”

Meeks presented research conducted by her colleague Gustavo Sbatella during the 2016 Wyoming Weed Management Rendezvous, held in Casper Jan. 19-21.

Controlling mallow

“Venice mallow is hard to find on herbicide labels,” Meeks added. “There aren’t a lot of products that specifically list Venice mallow as a species they control. Part of that is because there isn’t a lot of information available.”

Venice mallow as a weed is specific to dry beans, meaning it does not impact other crops.

“This weed is specific to dry bean production in the West, and a lot of herbicide label information comes from the Midwest where Venice mallow isn’t a problem,” she said.

In addition, controlling the weed is particularly important because many Wyoming dry bean producers are producing beans for seed.

“Certified seed producers need their product to be very clean,” Meeks explained. “Late season weeds can affect the certification. Venice mallow is a particular problem because there are several flushes. It can germinate throughout the growing season.”

Weed control study

To address concerns with the weed, Meeks said that UW conducted a study in Burlington to determine the crop response and efficacy of various weed control programs.

“We planted a variety of pinto beans called Othello in 22-inch rows, with a target population of 65,000 seeds per acre,” she explained. “The beans were planted on June 1.”

The soils planted were gravelly and sandy loam soils, both areas where Venice mallow thrives. Plots were 11 by 25 feet and randomized.

Weed counts were taken three times in the season – immediately before post-emergence application of herbicide, 15 days after post-emergence application and right before harvest on Sept. 1.

Two different pre-plant treatments were utilized in the study. The first treatment was Eptam at three pints per acre with Sonalan at two pints per acre. The second treatment used Eptam at the same rate and Outlook at 14 fluid ounces per acre.

In considering post-emergence herbicide, Meeks noted, “The total season application of Outlook can’t be greater than 21 fluid ounces per acre, so we used seven ounces in the post-emergence application if we had used 14 in the pre-plant.”

She added that if no Outlook was used in the pre-plant scenario, all 21 fluid ounces were applied at post-emergence.

“The other post-emergence herbicide we used was Permit for residual control of weeds,” Meeks said. “Outlook and Permit are the only two herbicides labeled for both beans and Venice mallow.”

Results

Looking at results, Meeks noted that pre-plant treatments did not affect the number of Venice mallow plants in a statistically significant manner.

“We did see smaller Venice mallow plants, but there was not necessarily a density difference,” she clarified. “All of the treatments we compared to our weedy check significantly reduced density after treatment.”

She did mention that application of Permit did result in some weeds in the middle of their plots, but Venice mallow was still significantly reduced as compared to the non-treated, weedy check plot.

Meeks also said that yield differences were not seen between post-emergence herbicide treatments.

“We also wanted to look at this for purposes of getting seed certified for sale, and all but one treatment was approved for seed certification,” she noted.

Meeks added, “The other good thing is that there was no visible crop injury that was seen with any treatment.”

Caution

While all herbicide treatments were effective at controlling Venice mallow in beans, Meeks emphasized that producers be cognizant about the herbicides they use relative to crops they plan to plant in their next rotation.

“We have to think about cropping rotation restrictions with the use of these herbicides,” she said. “With Outlook, which had good control, we have to wait four months to plant winter barley and the next season for spring barley, sugarbeets and sunflowers.”

Meeks continued, “Where we get into trouble is with Permit. We can’t rotate to sugarbeets for three years after using Permit, which could present a problem.”

Additionally, sunflowers can’t be planted for 18 months after using Permit.

Meeks also noted that UW plans to repeat the study in the coming year, also focusing on nightshade control.

“We want to make sure we didn’t have a good year, good moisture or something else that may have affected the results,” Meeks said.

Saige Albert is managing editor of the Wyoming Livestock roundup and can be reached at saige@wylr.net.