HPIPM:Alfalfa Weeds

Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Rosanae
Order	Fabales
Family	Fabaceae
Subfamily	Faboideae
Tribe	Trifolieae
Genus	Medicago

Scientific Name

Medicago sativa

Common Name

alfalfa

Alfalfa(Medicago sativa)

Compiled by: Rachel Soto, Montana State University, Meagher County Extension, and

Marjolein Schat, Montana State University from the following sources:

http://cru.cahe.wsu.edu/CEPublications/eb1523/eb1523.pdf

http://plants.usda.gov/factshhet/pdf/fs_mesa.pdf

Identification and Life Cycle

Alfalfa (Medicago sativa) is a long-lived perennial in the pea family (Fabaceae) that is cultivated for livestock feed. Alfalfa stems are erect, grow from a woody crown and are 2 to 3 feet tall. New growth is originated from buds on the root crown. Leaves are alternately arranged on the stem and have three leaflets. Flowers are in loose clusters and vary in color from white to purple. Seed pods vary from sickle shape to spiral shaped and each pod contains several kidney shaped seeds. Alfalfa has a tap root that may penetrate deep into the soil.

Habitats

Alfalfa grows best on deep, well-drained soils.

Impacts

Volunteer alfalfa may displace desirable vegetation.

Biology and Ecology

Alfalfa propagates from seed. Fresh seeds do not germinate as well as seeds that are 2-3 years old. Seedlings are susceptible to competition from other plants for light, nutrients, and water, however mature plants have a deep-penetrating root which makes them fairly drought resistant. Flowers develop from May through July and fruits form in late summer and fall.

Management Approaches

Once established in subsequent crops, alfalfa can be difficult to remove, in particular if the subsequent crop is also a broadleaved crop. Strategies that combine mechanical control and chemical control in fall after the alfalfa harvest can reduce the impacts of volunteer alfalfa the following spring.

Biological Control

There are no biological controls available for alfalfa.

Mechanical and Cultural Control

If the last harvest is timed so that re-growth reaches 4-6 inches before hard frost, disking or rotary tilling 7-10 days after herbicide application breaks ups alfalfa crowns. Subsequent deep tilling will bring roots to the surface where they will desiccate or freeze.

Chemical Control

A variety of herbicides can be used to control alfalfa. For herbicide recommendations for specific grain rotations and weeds in Montana, please see the MSU Herbicide Chooser Tool.

Examples of herbicides that can be used to manage alfalfa

Consult herbicide labels for additional rate, application, and safety information. Additional herbicide information can be found at http://www.greenbook.net.

Herbicide Active Ingredient trade name	Mode of Action	Product per Acre	Application Time or Growth Stage
Corn
Dicamba, diflufenzopyr, nicosulfuron	Action like indole acetic acid (synthetic auxins), Inhibition of acetolactate synthase ALS (acetohydroxyacid synthase AHAS)
*Celebrity Plus		4.7 ounces	Apply to actively growing weeds.
Small Grains
2,4-D, clopyralid	Action like indole acetic acid (synthetic auxins)
*Curtail		2 - 2.66 pints	Apply before alfalfa exceeds 3 inches in height.
Clopyralid, fluroxypyr	Action like indole acetic acid (synthetic auxins)
*Widematch		1 - 1.33 pints	Broadcast postemergence to actively growing wheat, barley or oats, from the 3 leaf crop growth stage up to the flag leaf emergence. Controls volunteer alfalfa from seed. Provides suppression of volunteer alfalfa from perennial plants.
Alfalfa
Glyphosate	Inhibition of EPSP synthase
*Roundup Original Max		1 - 1.5 quarts	Make application after the last hay cutting in fall. Allow alfalfa to re-grow to a height of 6-8 inches prior to treatment.
Fallow
Glyphosate	Inhibition of EPSP synthase
*Roundup Original Max		1 - 1.5 quarts	Make application after the last hay cutting in fall. Allow alfalfa to regrow to a height of 6-8 inches prior to treatment.

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.

References

For more images please visit IPM Bugwood. http://www.ipmimages.org/search/action.cfm?q=Medicago%20sativa