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Publication #SS-AGR-07

Weed Management in Small Grains Harvested for Grain1

J.A. Ferrell, G.E. MacDonald, and R. Leon2

Successful weed control in small grains involves using good management practices in all phases of production. In Florida, winter weeds compete with small grains for moisture, nutrients, and light with the greatest amount of competition occurring during the first six to eight weeks after planting. Weeds also cause harvest problems the following spring when the small grain is mature.

Crop Competition

Crop competition is one of the most important tools in weed control, but it is often one of the most overlooked. A good small grain stand that emerges rapidly and shades the soil surface is helpful in reducing weed competition.

Utilizing good management practices is necessary for producing maximum small grain yields and is also an aid in weed control. The plant that emerges first and grows most rapidly is usually the plant that will have the competitive advantage; therefore, everything possible should be done to ensure that the small grain, not the weed, has this competitive advantage. For optimum management practices, follow Florida Cooperative Extension Service recommendations.

Know Your Weeds

Know your weeds and choose the herbicide that is effective for your specific weed problem (Table 2). In Florida, small grains are infested with several species of winter weeds, most of which can be controlled by the phenoxy type herbicides, namely 2,4-D. However, some species that inhabit Florida small grain fields may not be controlled by 2,4-D. Proper identification is crucial for controlling wild radish (Raphanus raphanistrum), which is often confused with wild mustard (Brassica kaber). Wild radish is ubiquitous throughout Florida and is not easily controlled with 2,4-D. Table 2 provides herbicide effectiveness on weed species. Wild mustard occurs sparsely within the Florida small grain growing region and can easily be controlled with applications of 2,4-D. Most producers refer to both species as "Wild Mustard," therefore compounding the identification problem. If wild radish is misidentified, the degree of weed control given by 2,4-D applications may be inadequate. It should be understood that 2,4-D does have activity on wild radish but the restriction of 2,4-D applications tied to small grain size usually allows the wild radish to get too large to be controlled. Wild radish can be controlled by 2,4-D up to 6 inches or the 3-leaf stage. The confusion of wild mustard and wild radish is the most notable instance where a misidentification can cause substandard weed control in small grains.

Chemical Control

Proper choice of the herbicide and rate applied are extremely important for weed control in small grains (Table 1). Postemergence herbicides combined with the previously discussed management practices are important for ensuring that the small grain crop has the initial competitive edge. Herbicide applications should be made to small weeds unless specifically stated on label or recommendations.

The most widely used herbicide in small grains is 2,4-D. Small grains vary in their tolerance to 2,4-D depending upon the growth stage when the herbicide is applied and the particular crop planted (Table 1). Generally, wheat varieties are the most tolerant, barley is intermediate, and oats are least tolerant to 2,4-D. Rye is intermediate between wheat and barley. As a general rule, the least injury to the grain crop with the use of 2,4-D can be expected when it is applied from the 3-4 tiller to full tiller stage. Applications made after jointing will result in grain head injury and possible reduction in seed fill.

Most herbicides labeled for weed control in small grains belong to or are similar to the organo-auxin herbicide group and do have some potential for off-target spray drift. Care should be taken to avoid spray drift to sensitive crops. Furthermore, the State of Florida has restrictions and prohibitions on organo-auxin herbicides used within the state. Refer to fact sheet SS-AGR-12 Florida's Organo-Auxin Herbicide Rule - 2012 (http://edis.ifas.ufl.edu/wg051) for information concerning this rule.

The herbicides suggested are those that have performed well in IFAS research. Read and follow all label instructions and precautions. Accurate sprayer calibration is extremely important since rates too low may not provide adequate weed control and rates too high may injure the crop. Herbicides, like any pesticide, should be handled with care. Store herbicides behind locked doors in the original containers with the label intact, and separated from seed, fertilizers, and other pesticides.

Tables

Table 1. 

Weed control in small grains.

Trade Name and Rate of Commercial Product

Per Acre

Common Name and Rate of Active Ingredient Per Acre

Remarks

2,4-D1

Several Brands

(0.5 - 2.0 pt of

4 lb/gal amine or low-volatile ester formulation)

2,4-D

(0.25 - 1.0 lb)

For control of winter annual broadleaf weeds and suppression of wild garlic and onion. Apply after small grain has produced 3-4 tillers or has fully tillered but before jointing. In most years this occurs in February. Weed control will be best if temperatures are 60°F or greater at application. See label for grazing restrictions. Only amine or low-volatile ester formulations are legal for application in Florida. Yield reduction will often result if 2,4-D is applied during jointing stage of wheat. If mixing with liquid fertilizer, amine must be preslurried in with water before adding tank and strong agitation is required.

Banvel1

or

Clarity,

others

(4 - 8 fl. oz)

dicamba

(0.125 - 0.25 lb)

Controls many annual broadleaf weeds and suppression of wild garlic and onion. Apply after winter dormancy but before small grain begins to joint. Apply when weeds are in 2-3 leaf stage and rosettes are <2" across. Check label for grazing restrictions. Yield reduction will occur when treatment is applied to jointing wheat.

Banvel1

(0.25 pt)

+

2,4-D

(0.5 pt)

dicamba

(0.125 lb)

+

2,4-D

(0.25 lb)

Combination controls a broader spectrum of weeds than dicamba or 2,4-D alone. Apply after winter dormancy but before grain begins to joint. This combination may cause some crop injury. Check label for grazing restrictions.

Buctril 4EC

(0.75 - 1 pt)

bromoxynil

(0.375 - 0.5 lb)

For control of wild radish and many other small, annual broadleaf weeds. Apply after small grain emerges, but before weeds are in the 3-4 leaf stage. Do not apply to small grain during or after boot stage. Do not graze treated fields for 30 days after application. May be tank-mixed with Hoelon. See label for tank-mixing instructions.

Harmony Extra 75 DF

(0.3-0.6 oz)

or

thifensulfuron + tribenuron

For control of broadleaf weeds postemergence in wheat. Beneficial in Florida for the control of wild radish. Application should be made to rosettes less than 6" in diameter. Application must be made no later than 30 days after weed emergence with fall application made before plants harden off. Always use a nonionic surfactant (80% active at 0.06 - 0.50% v/v) and carefully read label directions for spray tank clean-out. For increased control of severe wild radish infestations or wild radish emerged greater than 30 days, apply either herbicide in combination with MCPA at 0.25 lb active ingredient per acre.

Express

(0.16 - 0.33 oz)

tribenuron-methyl

(0.02 - 0.04 lb)

Hoelon 3EC2

(2.0 pt)

diclofop-methyl

(0.75 lb)

For postemergence control of annual ryegrass in wheat. For best results apply when ryegrass is in the 1-5 leaf stage and before wheat begins to joint. Thorough uniform spray coverage of ryegrass is essential. May be mixed with Buctril for broadleaf control. Do not graze for 28 days after treatment. Do not apply 2,4-D or dicamba within 5 days of application or reduced grass control will be observed. A crop oil concentrate should be added at 1 qt/A. Diclofop-resistant ryegrass has been found in several areas of the country so resistance management is essential.

MCPA

Several brands

(0.5 to 1.0 pt of 4 lb/gal)

MCPA

(0.24 to 0.5 lb)

For use in wheat, rye, oats, and barley. Apply after two tillers but before jointing. Apply when weeds are less than 2 inches in height or less than 2 inches in diameter. May be tank-mixed with several materials; Express + MCPA is very effective on several weeds.

Metribuzin

(2 - 8 oz)

metribuzin

(0.094 - 0.38 lb)

For control of henbit, chickweed, ryegrass, and other winter annuals. Apply after 2-leaf stage, but before jointing. Application rate is dependent on plant size, see product label for specific information. Use only on label recommended varieties or severe crop injury may result. For barley and wheat only.

1See fact sheet SS-AGR-12 Florida's Organo-Auxin Herbicide Rule - 2012 (http://edis.ifas.ufl.edu/wg051)for state rules pertaining to application of organo-auxin herbicides in Florida. READ and FOLLOW all label instructions and precautions when applying any pesticide.

2Restricted Use Pesticide

Table 2. 

Estimated effectiveness of herbicides on common weeds in Florida small grains.1

WEEDS

Herbicides

2,4-D

Banvel

Buctril

Hoelon

MCPA

Sencor

Harmony Extra

Express

Wild mustard

G

E

G

P

G

G-E

E

E

Wild radish

G

G

F-G

P

G

G

E

E

Henbit

F-G

G

F-G

P

P-F

E

G

-

Evening primrose

G

G

G

P

E

G

E

F

Shepherds purse

G

G

E

P

G-E

E

E

-

Wild garlic

F

G

P

P

P

-

G-E

P

Common ragweed

G

G-E

E

P

F-G

G

P-F

-

Pigweeds

E

E

E

P

G-E

G

E

-

Thistles

G

G

G

P

G

-

F-G

-

Dandelion

E

E

E

P

E

-

-

-

Plantains

E

E

E

P

E

-

E

-

Curly dock

E

E

F-G

P

P

-

E

G

Dogfennel

G

E

E

P

F

-

E

-

Horsenettle

F

G

F

P

G

-

-

-

Horseweed

F

F

P

P

F

-

G

-

Goldenrod

F

F

P

-

G

-

-

-

Annual ryegrass

P

P

P

E

P

F-G

P

P

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

Weed Control Symbols: E = 90-100% control; G = 80-89% control; F = 60-79% control; P = Less than 60% control; - = insufficient observations.

Footnotes

1.

This document is SS-AGR-07, one of a series of the Agronomy Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Revised December 2011. Reviewed, with minor revision September 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 R. Leon, assistant professor, 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.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

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.