1Zollinger et al. 1998. NR = Not Reported.

Weed Management

Weed control in small grains is generally required to achieve a profitable yield. Broadleaf weeds, foxtails, and wild oat infest small grains statewide. The use of the proper cultural control techniques plus the use of chemical controls may be required to control troublesome weeds.

Herbicides most commonly used in 1996 were; 2,4-D, MCPA, and Tribenuron. They were applied to 45%, 23%, and 17% of the barley acreage respectively. A total of 3,815,000 acres of barley were treated in 1996. The producer applied 90% of the herbicides to barley and 92% was applied by ground equipment.

Foxtails: Green foxtail (Setaria viridis), Yellow foxtail (Setaria glauca).

Commonly found in field crops across North Dakota, often called pigeongrass. One of the states most serious and widespread annual weeds. Foxtails are most competitive when barley is seeded late and soil temperatures are warm which promotes foxtail germination and growth. Heavy infestations will cause increased elevator dockage, harvest complications and moisture stress during droughty conditions.

Tillage is one of the best strategies for reducing foxtail infestations. Fall moldboard plowing can bury foxtail seed preventing emergence the following spring. Infestations with less than 30 plants per square foot, and foxtails emerging into a crop at the three to four-leaf stage, generally do not require control. At these levels of infestation the crop can usually out-compete foxtail. Heavy infestations with more than 100 plants per square foot require chemical control. Moisture stress and foxtails emerging before or at the same time as the crop can complicate the decision process. Under these conditions yield losses can be more severe.

Kochia: (Kochia scoparia)

Is an erect bushy annual, two to seven feet in height. It is an exceptionally competitive weed that can cause severe yield losses. This weed is commonly found in most crops in the state of North Dakota. Kochia is one of the first weeds to germinate in the spring but is late in maturing. Kochia has become difficult to control. In many fields 2,4-D and MCPA herbicides no longer control kochia due to the presence of resistant kochia populations. Some kochia populations have become resistant to ALS, triazine, and dicamba herbicides.

Tillage can be an effective practice for controlling kochia. Tillage in the spring before planting and in the fall following harvest can reduce infestations of this highly competitive weed. Tillage is also a strategy for minimizing herbicide resistant plants. Mechanical removal of any resistant plants will prevent seed production and slow the spread of resistant plants.

Herbicide treatments are applied to small plants (less than 3 inches tall). Spray coverage should thoroughly wet the weed foliage. Fluroxypyr provides good control of ALS, triazine, and dicamba resistant kochia. Dicamba plus MCPA amine and bromoxynil plus MCPA also provides good control.

Wild Oat: (Avena fatua)

Wild oat is a cool season annual, one to four feet tall. It is native to Europe but is common throughout much of western North America, including all of North Dakota. Wild oat is one of the most serious weed problems in small grains. It germinates quickly in the spring and can out-compete small grains resulting in severe yield losses. It is difficult to eradicate because the plants drop their seed prior to the crop being harvested. Seed dormancy results in delayed germination.

Delaying seeding is one of the most practical methods of culturally controlling wild oats. By delaying seeding, one or more cultivations can be made to destroy emerged wild oats prior to seeding the crop. Harrowing emerging wild oats following crop seeding may also be effective in reducing wild oat populations before the crop emerges.

Pre-emerge herbicides applied in the fall or spring prior to seeding can provide effective wild oat control. Products such as triallate and triallate + trifluralin (Buckle) can be applied to the soil and incorporated with tillage equipment in advance of seeding. This practice can save the producer time during the growing season and simplifies the timing of herbicide applications. Herbicides applied to the crop after emergence require careful timing of the treatment. Timing treatment at the proper growth stage of the wild oat and the crop is essential for optimum wild oat control. Careful reading of the herbicide label provides the necessary information as to when and how much product to apply.

Redroot pigweed: (Amaranthus retroflexus)

Redroot pigweed is a coarse erect annual, usually two to three feet tall. The lower stems are usually red, with color continuing down to the taproot. Redroot is widely distributed throughout the western states and commonly found in crops across North Dakota. Large populations of this weed can compete with small grains resulting in moisture stress and yield loss during droughty conditions.

Tillage prior to planting and on fallow ground is an effective way to reduce pigweed populations. The ALS herbicides, dicamba, and 2,4-D also give good control. The label provides necessary information on when to apply and how much product to use.

Russian Thistle: (Salsola iberica)

A rounded, bushy, much branched annual, usually one half to three feet tall. Seeds are spread as mature plants break off at ground level and are scattered by the wind as tumbleweeds. Russian thistle was introduced from Russia in the late 1800's and has become a common and troublesome weed in the drier regions of North Dakota. Under good crop conditions, small grains can out-compete Russian thistles.

Tillage prior to planting and on fallow ground is an effective way to reduce Russian thistle populations. Seedling plants have fleshy leaves so herbicide applications should be made by this growth stage or earlier. ALS herbicides, dicamba, 2,4-D, and bromoxynil provide good control.

Field Bindweed: (Convolvulus arvensis)

Field bindweed (creeping jenny) is a perennial weed introduced from Europe that is well adapted to North Dakota's climate. It can be found across the state and has been declared a noxious weed by the state of North Dakota. Bindweed has a deep root system that competes with crops for water and nutrients. It is easily spread by seed and root fragments. Field bindweed can reduce yields by 50 percent, cause lodging, and can make harvest difficult.

Intensive cultivation can control newly emerging seedlings, and aid in controlling established bindweed stands by reducing nutrient reserves in the roots. When used in combination with herbicides, cultivation becomes a key part of an effective management program.

Control of bindweed requires a long-term management program. Multiple herbicide applications are required to control bindweed. Herbicides should be applied when the bindweed is actively growing and at least 12 inches long. Field bindweed is more difficult to control in semiarid regions of Central and Western North Dakota due to slower herbicide uptake and reduced translocation when plants are moisture and heat stressed. Systemic herbicides work best to kill the extensive root system of bindweed. 2,4-D, dicamba, picloram (Tordon) and glyphosate (Roundup) are all effective systemic herbicides capable of controlling bindweed.

Canada Thistle: (Cirsium arvense)

Canada thistle is a colony-forming perennial weed with an extensive root system. Plants are one to four feet tall with spiny-leaves. Canada thistle is a native of Southeastern Eurasia. It was introduced into Canada in the late 18th century. It has become a major problem throughout North Dakota as a result of reduced tillage practices, wet weather cycle, and lack of effective controls. Canada thistle is an aggressive noxious weed that competes well with small grain for water and nutrients.

Periodic tillage on fallow ground is used to control Canada thistle throughout the summer. Tillage keeps the thistle plants in the rosette stage and prevents them from bolting. Following tillage, a herbicide such as glyphosate or clopyralid can be applied to the rosettes in late September or early October.

Post-harvest treatments give better thistle control than pre-harvest treatments. The highest rate allowed can be used without interfering with next year’s crop. Tillage can be a critical factor. Tillage in late fall, after spraying, increases control, adding an additional 30 to 40% control to treatment. Canada thistle can be controlled in wheat with clopyralid, or some sulfonylurea herbicides in tankmix with 2,4-D and dicamba. The maximum rate should be used.

Common Milkweed: (Asclepias syriaca)

A stout perennial weed that spreads by seeds and long deep roots. The plant is two to four feet in height and has a milky latex sap. It has become a severe weed pest in North Dakota due to it’s extensive root system, the wet weather cycle, tolerance to many herbicides, reduced tillage, and the lack of persistence by chemical and cultural controls. Milkweed can be a severe pest in wet regions of the state, competing with the crop for nutrients.

Preventing establishment and spread of milkweed patches requires continuous scouting and implementation of control efforts. Tillage in the spring, prior to planting, or in the fall after harvest aids in the reduction of milkweed populations. Tillage is also a way to address problems with milkweed tolerance to herbicides. The plants can be removed by cultivation, reducing the need for repeated herbicide applications.

Milkweed control is expensive. Patch spraying allows the use of higher herbicide rates with less expense than if an entire field was sprayed. Apply herbicides when milkweeds are in the late-bud to flowering stage and actively growing. Control patches when plants are small. Use glyphosate prior to heading of small grains. After heading, patch-spray with Tordon.

Table 6. Registered herbicides and their usage in North Dakota to manage weeds in barley.

1Zollinger et al, 1998. NR = Not Reported.

Contacts

North Dakota Barley Council
505 40^th Street SW
Fargo, North Dakota

Phillip Glogoza
Extension Entomologist
Department of Entomology
North Dakota State University

Marcia McMullen
Extension Plant Pathologist
Department of Plant Pathology
North Dakota State University

Richard Zollinger
Extension Weed Specialist
Department of Plant Sciences
North Dakota State University

References

Beard, L. and G.E. Waldhaus. 2000. North Dakota agricultural statistics, 1999. Ag Statistics no. 68. North Dakota State
        University, Fargo, N.D.

Glogoza, P.A. 2000. 2000 Field crop insect management guide. NDSU Extension Service. Extension report E-1143.

McMullen, M.P. & H.A. Lamey. 2000. 2000 Field crop fungicide guide. NDSU Extension Service. Extension report PP-622.

Stefenson, B., J. Pederson, and V. Pederson. 1999. Common barley diseases in North Dakota. NDSU Extension Publication
        PP-894.

Zollinger, R.K., G.K. Dahl, M.P. McMullen, P.A. Glogoza, A.G. Dexter, S.A. Fitterer, G.E. Waldhaus, & K. Ignaszewski.
        1998. Pesticide use and pest management practices for major crops in North Dakota 1996. NDSU Extension Service.
        Extension report no. 43.

Zollinger, R.K. 2000. 2000 North Dakota weed control guide. NDSU Extension Service. Extension Circular W-253.