NDSU Crop and Pest Report
Weeds


ISSUE 14  July 31, 2003

CONTROLLING LARGE WATERHEMP IN SOYBEAN WITH GLYPHOSATE

Weed scientists with the University of Missouri-Columbia have investigated lack of waterhemp control following glyphosate applications in Missouri. In the majority of cases, lack of control was likely due to inadequate rates of glyphosate applied on weeds too large or under some environmental stress. The general symptoms observed include death of the apical meristem, but regrowth of the axillary meristems. In addition, adventitious roots have formed on some of these plants.

Glyphosate labels list an application rate equivalent to 1.75 qt/A of 3 lb ae/gallon formulation (1.13 lb ae/A) for waterhemp less than 12 inches tall. For waterhemp larger than 12 inches, no rate is given. Recently, Monsanto sent out a flyer with guidelines for waterhemp control. For waterhemp greater than 12 inches, the guidelines suggest glyphosate equivalent to 2 qt/A (1.55 lb ae/A) (the maximum rate of glyphosate per single application in soybean), which corresponds to 44 oz./Acre Roundup WeatherMax, 52 oz./Acre Roundup UltraMax and 64 oz./Acre Roundup Original (add non-ionic surfactant with Roundup Original).

Regional agronomists have observed corn borer damage on waterhemp plants. It is possible that an infestation of corn borer in waterhemp could reduce glyphosate efficacy, much like others have observed with giant ragweed in Indiana and Illinois.

 

LAMBSQUARTERS CONTROL WITH GLYPHOSATE

There have been questions and reports of lack of common lambsquarters control with glyphosate. Field inspections have been made some observations follow.

Applications delayed by wet weather: It was common this spring and early summer for late herbicide application beyond the labeled range and size of weeds. Late glyphosate applications is the decisive factor to show those weeds that exhibit some tolerance to glyphosate as they increase in size.

Sprayer boom height: Sometimes the lambsquarters appeared in "rows" indicating low boom height. Low boom is desirable to avoid drift but proper boom height must be maintained for a proper overlapping pattern.

Crop canopy: A report from weed scientists in Wisconsin found several 4 to 8-inch common lambsquarters escaping glyphosate. The plants appeared to survive but many would have been shaded out by the pure weed control attributes of a strong, vigorous growing crop, like seeded soybean. The escapes were sprayed a second time with 1 to 2 qt/A of a 3 lb ae/gal glyphosate formulation. The healthiest plants were flagged and the soybean were trampled down around the lambsquarters plants to negate any canopy effect. The study is being monitored for results.

The question could be asked if the soybean plants intercepted to glyphosate which caused the lack of lambsquarters control. In this field the stand was not thick and all other weeds were controlled. It appeared that the lack of control was unique to the lambsqaurters. Rate, water volume, use of NIS and or AMS, time of day at app., size of the weeds, and any stresses the plants might be growing under all impact weed susceptibility to glyphosate.

 

CLEARFIELD WHEAT LAUNCHED IN PACIFIC NORTHWEST

After more than seven years in development, the nation's first herbicide-tolerant wheat is released in the Pacific Northwest. Several members of the Pacific Northwest wheat industry learned about the CLEARFIELD Production System for wheat and ClearFirst, the first new CLEARFIELD variety developed and marketed by General Mills. BASF launched the new technology simultaneously to seed retailers, ag chemical retailers and grain merch.

 

USE OF BIOTECH CROPS INCREASES

ND producers have embraced biotech soybeans and to a lesser extent, biotech corn, and are among the nation's top users of these new tech., according to a June 30 USDA report. The Ag. Statistics Service selected farmers from across the U.S. in June to assess planted acres. Questions included whether farmers had planted corn or soybeans that, through biotechnology, are resistant to herbicides, insects or both. Conventionally bred, herbicide resistant varieties were excluded and the insect resistant varieties include only those containing bacillus thuringiensis (Bt).

Not surprisingly, herbicide resistant soybeans constitute the majority of soybeans planted in Nebraska this year at 86%, a slight increase from 85% in 2002.

The following is the order of plant of biotech varieties as a percent of all soybeans planted: South Dakota (91%), Mississippi (89%), Indiana (88%), Kansas (87%), Nebraska (86%), Arkansas (84%), Iowa (84%), Wisconsin (84%), Missouri (83%), Minnesota (79%), Illinois (77%), Ohio (74%), North Dakota (74%), and Michigan (73%). The U.S. average of soybean acres planted to biotech varieties was expected to be approx. 81%, up from 75% last year.

Biotech corn plantings (52%) placed it third in the nation behind South Dakota at 75% and Minnesota at 53% and Nebraska (52%). The percentages of the total corn planted to a biotech hybrid ranged from a low of 9% to 75%, a much broader range than with soybeans. Percent of all corn planted to biotech hybrids for other states included: Kansas (47%), Iowa (45%); Missouri (42%), Wisconsin (32%), Illinois (28%), Michigan (35%), Indiana (16%) and Ohio (9%). In the US, a total of 40% of the corn was planted to biotech hybrids, up from 34% in 2002.

The states represented 81% of all corn acres and 89% of all soybean acres. Regarding corn production, the insect resistant varieties include only those containing bacillus thuringiensis (Bt) and the stacked gene varieties included those with both herbicide and insect resistance. The states for which these stats were reported represent 81% of all corn planted acres and 89% of all soybean planted acres.

The full USDA National Agricultural Statistics Service report was released Monday (June 30) and is available on the Web at:

http://www.usda.gov/nass/PUBS/TODAYRPT/acrg0603.txt

Richard Zollinger
NDSU Extension Weed Specialist
rzolling@ndsuext.nodak.edu


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