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Publication #SS-AGR-06

Weed Management in Sorghum 1

J.A. Ferrell, G.E. MacDonald, and B. J. Brecke2

Sorghum has the ability to tolerate short-term drought, and a late summer sorghum crop may follow an early-season corn crop. Weed control in sorghum is essential if high yields and efficient harvest are to be achieved; however, good weed control in sorghum is often difficult to achieve.

Sorghum is a small seeded grass and is relatively slow growing in the first few weeks after emergence. In addition, sorghum will not tolerate many of the herbicides that can be effectively used on corn. The slow seedling growth combined with the limited number of herbicides and low rates that must be used creates a problem in sorghum weed control. Another problem is that many of the herbicides normally used on sorghum either cannot be used or must be used at low rates due to the coarse texture of many Florida soils.

For these reasons it is essential that practices such as choice of hybrid, soil fertility, soil pH, moisture, and row spacing be optimized in an effort to give sorghum the best possible growing conditions to be as competitive as possible with weeds.

The most important consideration is control of grasses during emergence and seedling development of the sorghum. If grasses are not controlled at this stage and are as large as the sorghum, then cultivation will not control the grasses in the drill without killing the sorghum. Sorghum should not be planted in fields that are heavily infested with johnsongrass. If grasses can be controlled until the sorghum gets an initial height differential, cultivation can then be effective. If such a height differential is achieved, post-directed sprays can also be effective. Broadleaf weeds are a less serious problem since several materials can be effectively used for their control.

Table 2 should be used to determine which herbicides are most effective for the weeds anticipated or present in your situation. Then use Table 1 to determine rates and application recommendations. Proper calibration and application are essential since rates too low will result in poor control and rates too high may result in crop injury.

Tables

Table 1. 

Weed management in sorghum.

Trade Name and Rate of Commercial Product Per Acre

Common Name and Rate of Active Ingredient Per Acre

Remarks

PREEMERGENCE

Dual Magnum
1.0 - 1.33 pt

S-metolachlor

Use on seed that has been treated with a chemical safener such as Concep.1 If seed is not properly treated, severe injury will occur. Good control of many grasses and certain small seeded broadleaf weeds. Apply after planting before weeds and sorghum emerge. It can also be applied with fluid fertilizer.2

Stalwart, Parallel, others

1 - 1.3 pt

metolachlor

See above. Note that metolachlor products will commonly provide less soil residual control than those containing S-metolachlor.

Outlook, others

13 oz

dimethenamid-p

Similar to S-metolachlor. Less effective on tropical spiderwort.

POSTEMERGENCE

AAtrex or Atrazine3

(several formulations)

atrazine
1 - 2 lb ai/A

Apply after sorghum reaches the 3-leaf stage and before broadleaf weeds are 4" tall. For ground applications add emulsifiable oil concentrate at 1 qt/A. Do not apply more than 2 lb per application and do not apply more than 2.5 lb/A/season. Do not graze or feed forage for 21 days following application. A restricted-use pesticide.

Aim EC

0.5 - 1 oz

carfentrazone

Can be applied to sorghum from 30 days prior to planting to the 6-leaf collar growth stage. Controls many broadleaf weeds, but good coverage is essential. Addition of non-ionic surfactant (0.25% v/v) is required, but crop oil is not recommended due to increased crop injury. Directed applications are recommended if rates higher than 0.5 oz will be used. Expect moderate leaf burning from over-the-top applications. Do not apply to sweet sorghum.

2,4-D amine4
(several brands)
0.5 - 1 pt

2,4-D

Broadleaf weeds controlled. Sorghum is not as tolerant to 2,4-D as corn. Broadcast after sorghum is 6-8" tall. If sorghum is 10-15", use drop nozzles to direct spray toward base of plant. Over-the-top applications are most likely to result in herbicide injury. Do not treat sorghum in boot, tassel, or soft dough stage. Avoid drift.

Banvel, Clarity, Sterling4

0.5 pt

dicamba

Broadleaf weeds controlled. Apply from the 3-leaf stage until plant reaches 8" tall. Apply only as a directed spray on plants that are between 8" and 15”. Do not graze or feed treated sorghum, forage, or silage prior to mature grain stage. Avoid drift.

Basagran

1.5 - 2.0 pt

bentazon

Apply overtop before weeds exceed 4-6" in height. Grain sorghum should be fully emerged. Sorghum is very tolerant to bentazon, but do not apply to sorghum that is heading or blooming. Apply with a crop oil adjuvant at a rate of 1 qt/A.

Buctril 2EC

1 - 1.5 pt

bromoxynil

Apply to sorghum between the 3-leaf stage to 12" height or pre-boot stage to control most broadleaf weeds in 2-4 leaf stage of growth. Use 10 or more gallons of water per acre.

Lorox 4L

1 - 2 pt

linuron

Apply as a directed spray after sorghum is 12" tall. Use low rate when sorghum is 12-15" tall, and a sprayer equipped with skids, shoes, or shields. Use the high rate when sorghum is 15" tall and weeds are up to 4" in height. Make only one application per season. Add nonionic surfactant (1pt./25 gals. spray). DO NOT graze or feed plant parts to livestock within 3 months after application.

Gramoxone SL

1- 2 pt

Firestorm, Parazone, others

0.7 - 1.3 pt

paraquat

Controls grass and broadleaf. Apply as a directed spray when sorghum is a minimum of 12" tall and weeds are less than 3" tall. Do not spray higher than 3" on sorghum plant. Add nonionic surfactant at 1 qt per 100 gal of spray.

Peak 57DF

prosulfuron

Provides postemergence and residual controls of many annual broadleaf weeds. Apply after sorghum reaches 5" in height and before 30". Refer to the label for specific weed sizes, but as a general rule apply before weeds reach more than 4-6" high. The use of a non-ionic surfactant or crop oil is recommended. May be tank-mixed with Banvel, 2,4-D, or atrazine. Do not apply Peak within 15 days to sorghum treated with foliarly applied organophosphate insecticides. Do not graze within 30 days of application or harvest silage within 40 days of application. Do not apply to sweet sorghum. Rotational restrictions include the following: wheat, barley, rye, oats - 0 months; field corn - 1 month; peanuts, tobacco, cotton - 10 months.

Sandea

2/3 - 1 oz

halosulfuron

May be applied from the 2-leaf stage through layby (before head emergence) to control nutsedge and other broadleaf weeds. Do not apply more than 1 oz/A/yr. Applications to a stressed crop will increase injury for 7-10 days.

Prowl H20

1.5 pt

(culti-spray)

pendimethalin

For extended control of late-season grasses, cultivate so that brace roots and stems are covered and protected when sorghum is 4" in height or in the 2-leaf stage. Immediately spray with Prowl. If rainfall (0.5") is not received within 7 days after application, incorporate with a sweep-type or rolling cultivator. Can be tank-mixed with atrazine.

1Concep III, manufactured by Syngenta Corp., is a seed protectant applied to sorghum seed to minimize injury when the herbicides Dual Magnum or Dual II Magnum are used on sorghum for weed control. Screen, manufactured by Monsanto Company, is a seed protectant applied to sorghum seed to minimize injury when the herbicides Dual Magnum or Dual II Magnum are used on sorghum for weed control.
2Observations in wheat fields indicate crop damage when 2,4-D is tank-mixed with liquid nitrogen. This also may be evident with other herbicide-nitrogen mixtures. To avoid possible damage and obtain better weed control, herbicides and nitrogen should be applied separately.
3WARNING: THE FOLLOWING STATEMENT HAS BEEN ADDED TO THE ATRAZINE LABEL. THIS STATEMENT SHOULD BE HEEDED BY ALL PROSPECTIVE USERS AND STEPS SHOULD BE TAKEN TO COMPLY WITH THIS LABEL CHANGE.
ATRAZINE IS A CHEMICAL WHICH CAN TRAVEL (SEEP OR LEACH) THROUGH SOIL AND CAN CONTAMINATE GROUNDWATER AS A RESULT OF AGRICULTURAL USE. ATRAZINE HAS BEEN FOUND IN GROUNDWATER AS A RESULT OF AGRICULTURAL USE. USERS ARE ADVISED NOT TO APPLY ATRAZINE WHERE THE WATER TABLE (GROUNDWATER) IS CLOSE TO THE SURFACE AND WHERE THE SOILS ARE VERY PERMEABLE, i.e., WELL-DRAINED SOILS SUCH AS LOAMY SANDS. YOUR LOCAL AGRICULTURAL AGENCIES CAN PROVIDE FURTHER INFORMATION ON THE TYPE OF SOIL IN YOUR AREA AND THE LOCATION OF GROUNDWATER. IN ADDITION, SOME PRODUCT LABEL STATEMENTS INCLUDE AS A FURTHER QUALIFICATION OF RISKY SOILS, SOILS CONTAINING SINKHOLES OVER LIMESTONE BEDROCK, SEVERELY FRACTURED SURFACES, AND SUBSTRATES WHICH WOULD ALLOW DIRECT INTRODUCTION INTO AN AQUIFER.
4See fact sheet SS-AGR-12 Florida Organo-Auxin Herbicide Rule for state rules pertaining to application of organo-auxin herbicides in Florida.

Herbicide recommendations in this report are contingent upon their registration by the Environmental Protection Agency. If a registration is canceled, the herbicide would no longer be recommended.

Table 2. 

Estimated Effectiveness of Herbicides on Common Weeds in Florida Sorghum.1

WEEDS

Herbicide

Dual or Outlook

Basagran

Prowl

Atrazine

Dicamba or 2,4-D

Paraquat

Sandea

Aim

Peak

Buctril

Time of Application

PRE

POT

Culti-spray

POT

POT/PDS

PDS

POT

POT

POT

POT

BROADLEAF

Bristly starbur

P

G

P

E

G

G-E

G

-

-

F

Cocklebur

P

E

P

E

E

E

E

F

G

E

Florida beggarweed

F-G

F

F-G

G

G

G-E

P

-

-

F

Florida pusley

G-E

P

G-E

E

F

F

-

-

-

G

Morningglories

P

F

P

E

E

G

P

G

F

G

Pigweed

E

P

G

E

E

G-E

G

F

G-E

F

Ragweed

F

F-G

F

E

E

G-E

G

F

G

F

Sicklepod

P

P

P

E

E

F

P

P

F-G

P

GRASS

Crabgrass

E

P

E

F

P

E

P

P

P

P

Goosegrass

E

P

E

F

P

E

P

P

P

P

Johnsongrass

(from seed)

F

P

F

P

P

F

P

P

P

P

Sandbur

E

P

E

G

P

E

P

P

P

P

Texas panicum

P

P

E

F-G

P

E

P

P

P

P

SEDGE

Purple Nutsedge

P

P

P

P

P

F-G

G-E

P

P

P

Yellow Nutsedge

F

G

F

P

P

F-G

G

P

P

P

1 Estimated effectiveness based on herbicide rates recommended in this report. Effectiveness may vary depending on factors such as herbicide, size of weeds, time of application, soil type, and weather conditions.

Time of Application

PRE = Preemergence

POT = Postemergence broadcast

PDS = Directed postemergence

Weed Control Symbols

E = 90-100% control

G = 80-90% control

F = 60-80% control

P = Less than 60% control

Footnotes

1.

This document is SS-AGR-06, one of a series of the Agronomy Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Revised November 2007. Reviewed November 2010. Revised April 2012. Please visit the EDIS website at http://edis.ifas.ufl.edu.

2.

J.A. Ferrell, associate professor, Agronomy Department; G.E. MacDonald, professor, Agronomy Department, and B. J. Brecke, professor emeritus, Agronomy Department, West Florida Research and Education Center, Milton, FL; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication do not signify our approval to the exclusion of other products of suitable composition. Use herbicides safely. Read and follow directions on the manufacturer's label.


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U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.