Weed Control in Sugarbeets
K. Locke', R.L. Dove1 2 , and K.A. Rykbost 2
Introduction
Weed control has been a very important factor in commercial success
and profitability in sugarbeet crops in the Klamath Basin. Hand labor to
salvage problem situations is very expensive and not readily available. Delayed removal ofweed competition seriously reduces yield potential. Most of
the unprofitable sugarbeet fields in five years of commercial production in the
Klamath Basin were caused by weed control failures. A 1993 evaluation of
several post-emergence chemical treatments demonstrated a 40 percent yield
reduction when weed competition was left uncontrolled through the first 12
weeks of the growing season. The best chemical treatments evaluated
provided satisfactory weed control and profitable crop production. The 1993
study was repeated in 1994 with minor changes in procedures.
11111111■1111■111
Procedures
Sugarbeet weed control was studied on a site cropped with alfalfa in the
previous four years. Alfalfa was desiccated with Round-up herbicide in
August, 1993. Field preparation, fertilization, irrigation, and insect control
practices are described on pages 10 and 11. The sugarbeet variety WS 62
was planted in 22-inch rows on April 15 and hand-thinned to approximately
30,000 plants/acre on June 2. Individual three-row plots, 20 feet long were
established to accommodate seven weed control treatments and five replications. Chemical treatments were applied with an experimental plot sprayer in
20 gpa of solution on May 13 and May 25. Weeds were identified by
species and counted from a 15 square foot quadrant at the center of each plot
'/ Klamath County Cooperative Extension Agent, Klamath Falls, OR.
2/ Associate Professor and Superintendent/Professor, respectively, Klamath Experiment Station, Klamath
Falls, OR.
Acknowledgments: Partial funding from the CBGA, product supplied by NOR-AM Chemical
Company and E.I. du Pont de Nemours and Co., Inc., and sample analysis by Imperial Holly Sugar
Corporation are gratefully recognized.
Klamath Experiment Station
33
Weed Control in Sugarbeets
on June 30. All plots, including the untreated control, were hand weeded on
July 1.
Beets were harvested by hand on October 12. Yields were measured
from the center row of each plot. Approximately 30-pound sugarbeet
samples from each plot were analyzed for tare loss and sugar content. Total
sugar production and gross crop value were calculated as described on page
11.
Results and
Discussion
Sugarbeet plants and weeds were in the cotyledon to two-true-leaf
stage at the time of initial herbicide applications. Second herbicide applications coincided with two-to-four-leaf beet seedling development. Herbicide
treatments did not appreciably injure beet seedlings.
Weed species composition was influenced by the previous crop history.
Sheperdspurse and redstem filaree were the dominant weeds. These species
are not as aggressive or competitive as lambsquarter, redroot pigweed, and
hairy nightshade, which are more prevalent in a crop rotation including cereals
and potatoes. Sheperdspurse was not controlled by Upbeet at either rate
(Table 1). Betamix, alone or in combination with Upbeet, and NA3 08/1 at
the high application rate provided satisfactory control of sheperdspurse.
Filaree was not well controlled by any ofthe treatments. Betamix and
NA308/1 controlled other species (mostly lambsquarter and redroot pigweed) quite well. Common purslane was the most frequent species that
escaped control in these treatments. NA308/1 was more effective at the
higher rate. Upbeet was ineffective at either rate and did not improve weed
control when combined with Betamix.
In contrast to the 1993 study, where the control treatment experienced
a 40 percent yield reduction and a 1.5 percent reduction in sugar content,
effects ofherbicide treatments on beet yields and sugar content were less in
this study (Table 2). The main reason was the difference in weed species
between experiments. Lamb squarter and hairy nightshade were very competitive with beet seedlings in the 1993 study. Sheperdspurse and filaree are
smaller and were much less competitive. Earlier removal of weeds from the
plots in 1994 was also a factor. The four treatments that provided the best
34 Klamath Experiment Station
Weed Control in Sugarbeets
weed control were not significantly different in yield, sugar production, or
gross value. The control treatment was not significantly different from Upbeet
at the low application rate in yield, sugar production, or gross value. The
combination of Betamix and Upbeet and both rates ofNA3 08/1 produced
among the highest beet yields.
In two years of evaluations under very different weed species pressure,
Betamix and NA308/1 have provided acceptable control of most weeds
except redstem filaree. Upbeet has not been effective, and has not improved
weed control significantly when used in combination with Betamix. The most
difficult weed species in local sugarbeet crops, kochia and thistles, have not
occurred in these studies. Where weed distribution is similar to conditions in
these experiments, post-emergence applications ofBetamix or NA308/1 offer
a cost-effective approach for weed management. When chemical controls
fail, hand weeding should be employed as early as possible to reduce competition effects.
Klamath Experiment Station 35
Weed Control in Sugarbeets
Table 1.
Effects of repeated herbicide treatments on weed density in WS-62 sugarbeets at Klamath
Falls, OR, 1994.
Treatment
Control
Rate on May 13
and May 25
Weed density'
She perds purse
Filaree Other Total
ai / A
0
plants / sq. ft.
1.8
1.4
2.6
5.8
Betamix
0.33 lb + 0.50 lb
0.2
1.4
0.4
2.0
Upbeet &
Betamix
0.50 oz + 0.33 lb
0.50 oz + 0.33 lb
0.2
1.1
0.4
1.7
Upbeet2
0.50 oz + 0.50 oz
2.0
1.8
2.0
5.8
Upbeet2
0.75 oz + 0.75 oz
1.5
1.8
1.8
5.1
NA 308 / 1
0.25 lb + 0.33 lb
0.6
1.0
0.5
2.1
NA 308 / 1
0.3751b + 0.50 lb
0.2
1.3
0.2
1.7
1/ Weed density on June 30
2/ Included 0.25% surfactant
Table 2.
Effects of repeated herbicide treatments on yield, sugar content, total sugar production, and
gross value of WS-62 sugarbeets at Klamath Falls, OR, 1994.
Treatment
Control
Beet
yield
Sugar
content
Sugar
production
Gross
value
ai / A
tons /A
%
lb / A
S/A
0
26.7
18.2
9700
1250
Betamix
0.331b + 0.501b
30.1
17.9
10740
1370
Upbeet &
Betamix
0.50 oz + 0.33 lb
0.50 oz + 0.33 lb
33.1
17.0
11180
1400
Upbeet
0.50 oz + 0.50 oz
28.6
17.9
10240
1310
Upbeet
0.75 oz + 0.75 oz
29.5
18.0
10620
1360
NA 308 / 1
0.25 lb + 0.33 lb
31.0
17.4
10740
1360
NA 308 / 1
0.375 lb + 0.50 lb
30.6
17.3
10520
1330
29.9
9
3.4
17.7
4
1.0
10530
6
860
1340
6
110
Mean
CV (%)
LSD(0.05)
36
Rate on May 13
and May 25
Klamath Experiment Station