Cooperative
Extension
Service


University of Illinois
at
Urbana-Champaign


No. 15/July 3, 1998

Maximum Weed Sizes for Postemergence Soybean Broadleaf Herbicides

Surplus rainfall, hot temperatures, and delayed soybean planting all have combined to create significant broadleaf weed problems in many soybean fields. Fields that received a soil-applied herbicide before or immediately after planting have, in general, had less weed pressure than fields where no herbicide has yet been applied. In many of these "total post" fields, broadleaf weeds have become quite large, and control with postemergence herbicides may not be as complete as desired.

One "good" point with respect to past and current environmental conditions is that the weeds have not been under moisture stress conditions and are relatively "soft." This condition may translate into better activity from many postemergence broadleaf herbicides. Unfortunately, the soybeans are also "soft," which increases the likelihood for crop response following the postemergence herbicide application.

The following table is reproduced from the 1998 Illinois Agricultural Pest Management Handbook (Table 22, p. 82), and contains maximum broadleaf weed sizes as indicated on several postemergence soybean herbicide labels. The table lists only annual broadleaf weed species, but many of these herbicides also afford some suppression or control of certain perennial broadleaf species. Additionally, several of these herbicide labels indicate suppression of certain larger annual broadleaf species that are not included in this table. Tank mixes may broaden the control spectrum of a given herbicide, but consult the respective labels for spray additive recommendations and special precautions when tank-mixing herbicides.

Table 22. Soybean "post-broadleaf" herbicides: Maximum weed sizes and application rates.

Key to column heads:
A = Cocklebur, common
B = Jimsonweed
C = Lambsquartersa
D = Morningglories, annual (tall and ivyleaf)
E = Nightshade, eastern black
F = Pigweeds
G = Ragweed, common
H = Ragweed, giant
I = Sida, prickly
J = Smartweeds
K = Sunflower, wild
L = Velvetleaf

Herbicide Rate A B C D E F G H I J K L
ALS
translocatedb
oz/A Label weed height, in inches
Classic 0.50 6 4 - 2c - 2d - - - 2 5 -
Classic 0.75 12 6 - 4c - 4d 4 6 - 4 8 6
Concert 0.50 4 5 4 2c - 12 3c - - 8 8 8
FirstRate
84WDG
0.30 10 4 - 6 - - 10 10 - 6 12 6
Pinnacle 0.25 6c 4c 4 - - 8 - - - 6 6c 6
Pursuit
70DG
1.44e 8 3 2c 2 3 8 3 3 - 3 3 3
Raptor
1S fl oz
4-5 8 6 5 4c 5 8 5c 5 4c 5 8 8
Scepter
70DF
1.40 8 - - - - 4 - - - - 4 -
Scepter
O.T.fl oz
16.0 6 - - 2 - 4 - - 3c 2 4 -
Synchrony
STS
0.50 8 5 4 3c - 8 4 4c - 8 8 8
Other
translocated
Roundup
Ultra floz
24 18 - 8 2 12 18 6f
-12
4 2 6 18 3f
-6
Roundup
Ultra
32 24 - 12 4 12+ 24 8f-
18
6 3 8 18+ 4f
-12
Contact pt/A Label weed height, in inches
Basagran 1.0 4 4 1c - - - - - - 4 3 2
Basagran 2.0 10 10 2c - - - 3 6 4 10 8 6
Blazer,
Status
1.0 - 4 - 2 <2 <4 2 <2 - 4 - -
Blazer,
Status
1.5 2c 6 2c 4 2 4 4 3 - 6 - -
Galaxy 2.0 6 6 2c 2c <2 2 3 6 3 6 5 5
Storm 1.5 6 6 2c 2 2 3 3 6 2 6 - 2
Contact pt/A Label weed height, in leaf stage (number)
Cobra 0.67 6L 4L - 2L 6L 6L 6L 4L 4L 4Lc 2L 4L
Flexstar
H
1.25 6L 8L 2Lc 4L 6L 6L 6L 6L 2L 6L 2L 4L
Reflex 1.25 2L 6L 2Lc 2L 4L 4L 4L 4L - 4L - 2L
Resource 0.25 - - - - - 3L 2L - 2L - - 6L
Resource 0.50 3L 4L 3Lc - - 4L 6L - 4L - - 10L
Stellar 0.31 2L 4Lc 2Lc 3Lc 3L 3L 4L 2L 3Lc - - 6L
Stellar 0.44 4L 4Lc 2Lc 3Lc 4L 4L 4L 4L 3Lc - - 6L

SOURCE: 1998 Illinois Agricultutral Pest Management Handbook, p. 82.
aLambsquarters control is erratic with many herbicides.
bALS-resistant waterhemp is not controlled by ALS herbicides.
cSuppression or partial control only; may need supplemental control.
cRedroot pigweed only; smooth pigweed and waterhemp only suppressed.
eUse equivalent rate of other formulations.
fSmaller size is used south of Interstate 70 in Illinois.

Aaron Hager (hagera@idea.ag.uiuc.edu) and Marshal McGlamery (mmcglame@ uiuc.edu), Crop Sciences, (217)333-4424