WEED CONTROL IN ROUNDUP READY^{®} SUGAR BEETS WITH ROUNDUP^{®} PLUS SOILRESIDUAL HERBICIDES
Joel Felix and Joey Ishida
Malheur Experiment Station
Oregon State University
Ontario, OR, 2008
Introduction
Weed competition is one of the yieldlimiting 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 6090 days for total canopy closure. Dawson (1977) reported that annual weeds that germinate within 2 weeks after planting or in a 4week period after the twoleaf stage can reduce sugar beet root yield by 26 to 100 percent. Sugar beet growers have traditionally used preplant or preemergence (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 soilapplied 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 tankmixtures of soilresidual 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 tractormounted flexiplanter units with doubledisc 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 8inch 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 CO_{2}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 (2leaf stage) were applied on May 13, while POST treatments (4leaf stage) on June 5 were followed by a second POST application (8leaf 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 (2leaf 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 8leaf stage, compared to treatments that included Stinger^{®} at 10.7 fl oz/acre at either 4 or 8leaf 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 soilresidual herbicides provided seasonlong weed control, it was not different from the control provided by Roundup PowerMax alone. Further studies are needed to evaluate the possibility of using soilresidual herbicides to reduce the number of Roundup PowerMax standalone sequential applications from three to one or two per season.
References
Dawson, J. H. 1977. Competition of lateemerging weeds with sugar beets. Weed Science 25:168170.
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 
Lambsquarters 
Pigweed spp. 
Barnyardgrass 
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 
Lambsquarters 
Pigweed spp. 
Barnyardgrass 
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).
_{}
_{ }