WEED CONTROL IN ROUNDUP READY® SUGAR BEETS WITH ROUNDUP® PLUS SOIL-RESIDUAL HERBICIDES

Joel Felix and Joey Ishida

Malheur Experiment Station

Oregon State University

Ontario, OR, 2008

Introduction

Weed competition is one of the yield-limiting factors in most crop production systems. Weeds compete with sugar beets for light, nutrients, and water. Sugar beets are especially vulnerable to weeds because of their poor competitiveness at the early growth stage and before canopy closure. Sugar beet tolerance of weeds will vary depending on the predominant weed species, planting date, time of weed emergence relative to the crop, and environmental conditions. Newly emerged sugar beet seedlings are small, lack vigor, and take about 60-90 days for total canopy closure. Dawson (1977) reported that annual weeds that germinate within 2 weeks after planting or in a 4-week period after the two-leaf stage can reduce sugar beet root yield by 26 to 100 percent. Sugar beet growers have traditionally used preplant or pre-emergence (PRE) herbicides to control weeds that emerge together with the crop.

The introduction of Roundup Ready® (RR) sugar beets presents an opportunity for growers to employ a total postemergence (POST) weed management program. If root yields are to be maximized, the total POST weed management program will require diligent monitoring of weed cohorts that emerge in succession. Some argue that use of soil-applied herbicides is a sound way to minimize weed biotype selection and a viable practice to provide sustainable weed control. A field study was conducted at the Malheur Experiment Station in Ontario, Oregon to determine crop response to herbicide tank-mixtures of soil-residual herbicides in combination with RoundUp PowerMax® to control weeds in RR sugar beets.

Materials and Methods

A study was established during 2008 in a field that had been ripped, moldboard plowed, and disked several times to create a seedbed favorable for sugar beet growth. The field was well drained and had been planted to wheat the previous year. The predominant soil was an Owyhee silt loam with 1.9 percent organic matter, a pH of 7.2, and a cation exchange capacity of 11 meq/g of soil. The study was a randomized complete block design with four replications. Individual plots were 7.33 ft wide (4 rows) by 25 ft long. Roundup Ready sugar beet variety 'BTSCT02RR08' was planted on April 11, 2008, using tractor-mounted flexi-planter units with double-disc furrow openers and cone seeders fed from a spinner divider that uniformly distributed the seeds within the row. Sugar beet seeds were dropped at the rate of 8 seeds/ft of row and later thinned to 8-inch spacing between plants within a row. Counter® 15G (7.4 lb/acre) was applied on April 12, 2008 and Temik® 15G (10 lb/acre) on June 3. Sugar beets were fertilized on June 13 using a special blend fertilizer to supply 180 lb nitrogen, 20 lb potassium, and 3 lb zinc. The study was irrigated on a calendar schedule to maintain moisture in the top 12 inches of the soil profile. Herbicide treatments were applied using a CO2-pressurized backpack sprayer equipped with a boom fitted with four 8002EVS Teejet nozzles calibrated to deliver 12 gal/acre at 40 psi at 3 mph. Early POST treatments (2-leaf stage) were applied on May 13, while POST treatments (4-leaf stage) on June 5 were followed by a second POST application (8-leaf stage) on June 23. Plants within each plot were visually evaluated for crop injury and weed control at 9 and 24 days after the last POST herbicide application on July 2 and July 17, respectively, using 0 percent (no crop injury or no weed control) to 100 percent (complete crop kill or complete weed control) scale. Sugar beets were harvested on October 16 from 25 ft of the two center rows using a beet harvester. Sugar beet weight from each plot was multiplied by a factor of 0.90 to correct for tare. Sugar content and other sugar yield variables were determined in a laboratory at the Amalgamated Sugar Factory in Nampa, Idaho. Sugar concentrations were determined by multiplying measured sucrose by 0.98 to estimate the sugar that would have been lost to respiration if the beets had been stored in a pile. The percent sugar extraction was calculated using the formula:


Where Ext is percent sugar extraction, Cond is the electrical conductivity in mmho, and Sug is the percent sucrose concentration.

The data were subjected to analysis of variance and treatment means compared using the least significant difference (LSD, P = 0.05).

Results

There was no injury observed on sugar beet plants from the herbicides used in this study. Kochia, common lambsquarters, pigweed species, common barnyardgrass, and hairy nightshade control at 7 and 24 DAT was 99 percent across treatments (Tables 1 and 2). The sugar beet plants were severely outcompeted by weeds in the untreated control plots. Consequently, the untreated control had the lowest yield (4.9 tons/acre) in the study (Table 3). Root yield for different herbicide treatments ranged from 45 to 48 tons/acre. The estimated recoverable sugar (lb/acre) varied among treatments. The root yield was relatively highest when early POST (2-leaf stage) of Roundup PowerMax at 22 fl oz/acre plus Upbeet® at 0.5 oz/acre was followed by two sequential applications of Roundup PowerMax at 22 fl oz/acre at the 4- and 8-leaf stage, compared to treatments that included Stinger® at 10.7 fl oz/acre at either 4- or 8-leaf stage. The untreated control treatment had the lowest estimated recoverable sugar (1,215 lb/acre) whereas that for the herbicide treatments ranged from 11,108 to 12,591 lb/acre. The results suggest that while inclusion of soil-residual herbicides provided season-long weed control, it was not different from the control provided by Roundup PowerMax alone. Further studies are needed to evaluate the possibility of using soil-residual herbicides to reduce the number of Roundup PowerMax stand-alone sequential applications from three to one or two per season.

References

Dawson, J. H. 1977. Competition of late-emerging weeds with sugar beets. Weed Science 25:168-170.


Table 1. Weed control ratings at 9 days (7/2/2008) after the last POST herbicide application on Roundup Ready® sugar beets at Malheur Experiment Station, Oregon State University, Ontario, OR, 2008.

Crop

injury

Weed control

Treatment

Rate

unit

Application timing

Kochia

Lambs-quarters

Pigweed spp.

Barnyard-grass

Hairy nightshade

%

------------------------------- % --------------------------------

1

Untreated Check

51

a

0

b

0

b

0

c

0

b

0

b

2

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

3

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Upbeet

0.5

OZ/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

4

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Upbeet

0.5

OZ/A

2 leaf

Crop Oil Concentrate

0.8

PT/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

5

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Stinger

10.7

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

6

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

Stinger

10.7

FL OZ/A

8 leaf

7

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Selectmax

9.2

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf


8

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

97

b

99

a

99

a

Nortron

2.88

FL OZ/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

9

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Progress Ultra

17.2

FL OZ/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

10

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Dual Magnum

1.31

PT/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

11

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

Dual Magnum

1.31

PT/A

8 leaf

12

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Outlook

21

OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

13

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

Outlook

21

OZ/A

8 leaf

14

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

8 leaf

Outlook

21

FL OZ/A

8 leaf

Means within a column followed by the same letter are not significantly different (LSD, P = 0.05).

All treatments and each application timing included ammonium sulfate (5 gal/100gal).


Table 2. Weed control ratings at 24 days (7/17/2008) after POST herbicide application on Roundup Ready® sugar beets at Malheur Experiment Station, Oregon State University, Ontario, OR, 2008.

Crop

injury

Weed control

Treatment

Rate

unit

Application timing

Kochia

Lambs-quarters

Pigweed spp.

Barnyard-grass

Hairy nightshade

%

------------------------------- % --------------------------------

1

Untreated Check

75

a

0

b

0

c

0

b

0

b

0

b

2

Roundup PowerMax

21.3

FL OZ/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

3

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Upbeet

0.5

OZ/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

4

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Upbeet

0.5

OZ/A

2 leaf

Crop Oil Concentrate

0.8

PT/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

5

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Stinger

10.7

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

6

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

98

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

Stinger

10.7

FL OZ/A

8 leaf

7

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Selectmax

9.2

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf


8

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Nortron

2.88

FL OZ/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

9

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Progress Ultra

17.2

FL OZ/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

10

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Dual Magnum

1.31

PT/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

11

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

Dual Magnum

1.31

PT/A

8 leaf

12

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Outlook

21

OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

13

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

Outlook

21

OZ/A

8 leaf

14

Roundup PowerMax

21.3

FL OZ/A

2 leaf

0

b

99

a

99

a

99

a

99

a

99

a

Roundup PowerMax

21.3

FL OZ/A

8 leaf

Outlook

21

FL OZ/A

8 leaf

Means within a column followed by the same letter are not significantly different (LSD, P = 0.05).

All treatments and each application timing included ammonium sulfate (5 gal/100gal).


Table 3. Sugar content (%), sugar beet root yield, and recoverable sucrose estimates at Malheur Experiment Station, Oregon State University, Ontario, OR, 2008.

Sugar beet yield

Treatment

Rate

unit

Application timing

Sugar content

Root yield

Extractable sugar

Estimated recoverable sugar

Estimated recoverable sugar

%

ton/acre

%

lb/acre

lb/ton

1

Untreated Check

15

a

4.9

b

83.2

a

1,215

c

250

a

2

Roundup PowerMax

21.3

FL OZ/A

2 leaf

16

a

45.4

a

83.4

a

11,769

ab

260

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

3

Roundup PowerMax

21.3

FL OZ/A

2 leaf

16

a

48.0

a

83.2

a

12,591

a

262

a

Upbeet

0.5

OZ/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

4

Roundup PowerMax

21.3

FL OZ/A

2 leaf

15

a

45.0

a

83.2

a

11,300

ab

254

a

Upbeet

0.5

OZ/A

2 leaf

Crop Oil Concentrate

0.8

PT/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

5

Roundup PowerMax

21.3

FL OZ/A

2 leaf

15

a

45.0

a

82.6

a

11,108

b

248

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Stinger

10.7

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

6

Roundup PowerMax

21.3

FL OZ/A

2 leaf

15

a

44.9

a

81.8

a

11,143

b

248

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

Stinger

10.7

FL OZ/A

8 leaf

7

Roundup PowerMax

21.3

FL OZ/A

2 leaf

16

a

46.4

a

84.2

a

12,387

ab

268

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Selectmax

9.2

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf


8

Roundup PowerMax

21.3

FL OZ/A

2 leaf

16

a

47.0

a

83.4

a

12,163

ab

259

a

Nortron

2.88

FL OZ/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

9

Roundup PowerMax

21.3

FL OZ/A

2 leaf

15

a

47.2

a

83.0

a

11,937

ab

254

a

Progress Ultra

17.2

FL OZ/A

2 leaf

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

10

Roundup PowerMax

21.3

FL OZ/A

2 leaf

15

a

46.8

a

82.1

a

11,761

ab

251

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Dual Magnum

1.31

PT/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

11

Roundup PowerMax

21.3

FL OZ/A

2 leaf

15

a

46.4

a

81.7

a

11,649

ab

252

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

Dual Magnum

1.31

PT/A

8 leaf

12

Roundup PowerMax

21.3

FL OZ/A

2 leaf

15

a

47.4

a

81.7

a

11,589

ab

245

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Outlook

21

OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

13

Roundup PowerMax

21.3

FL OZ/A

2 leaf

15

a

48.4

a

82.1

a

11,925

ab

246

a

Roundup PowerMax

21.3

FL OZ/A

4 leaf

Roundup PowerMax

21.3

FL OZ/A

8 leaf

Outlook

21

OZ/A

8 leaf

14

Roundup PowerMax

21.3

FL OZ/A

2 leaf

15

a

47.5

a

82.7

a

12,129

ab

256

a

Roundup PowerMax

21.3

FL OZ/A

8 leaf

Outlook

21

FL OZ/A

8 leaf

All treatments and each application timing included ammonium sulfate (5 gal/100gal).

Means within a column followed by the same letter are not significantly different (LSD, P = 0.05).