Dan Undersander - Alfalfa Management Guide

Authors

Dan Undersander

Extension agronomist, forages University of Wisconsin

Mark Renz

Extension agronomist, weed control University of Wisconsin

Craig Sheaffer

Research agronomist University of Minnesota

Glen Shewmaker

Extension agronomist University of Idaho

Mark Sulc

Extension agronomist

The Ohio State University

The authors wish to thank reviewers from industry and various universities for their suggestions and everyone who supplied photos, including those not specifically mentioned:

Steve Bicen, University of Wisconsinanthracnose; aphanomyces, roots; Fusarium wilt, roots; Phytophthora, roots; root assessment; verticillium wilt, root

Dennis Cosgrove, University of Wisconsinautotoxicity

Jim Ducytitle page photo

Del Gates, Kansas State Universityalfalfa weevils

Craig Grau, University of Wisconsinaphanomyces, stunting; bacterial wilt, stunting; black stem, lesions; Fusarium wilt, field; Phytophthora, plant; sclerotinia; stand assessment; verticillium wilt, plants

B. Wolfgang Hoffmann, University of Wisconsinalfalfa plant, page 1; alfalfa flowers

Eric Holub, University of Wisconsinaphanomyces, seedling

Jeffrey S. Jacobsen, Montana State Universitynutrient deficienciesall except boron leaf (from Diagnosis of Nutrient Deficiencies in Alfalfa and Wheat)

Pioneer Hi-Bred International, Inc. alfalfa closeups; cover photo ; cow; inside cover

Lanie Rhodes, Ohio State Universityblack stem, leaves; common leaf spot; lepto leaf spot

Marlin E. Rice, Iowa State Universityalfalfa weevil, blister beetles; clover leaf weevils; grasshopper; pea aphids; plant bug, adults; potato leafhopper, adult; spittlebug; variegated cutworm

Judy A. Thies, USDA-ARSroot-lesion nematodes

John Wedberg, University of Wisconsinalfalfa blotch leafminer; clover root curculio, damage

Thanks also to Bruce Gossen and Real Michaud, research scientists at Agriculture and Agri-Food Canada, for their contributions to the disease maps.

This publication is a joint effort of:
University of Wisconsin-Extension,
Cooperative Extension

Minnesota Extension Service,
University of Minnesota

Iowa State University
Cooperative Extension Service

Published by:

American Society of Agronomy, Inc.
Crop Science Society of America, Inc.
Soil Science Society of America, Inc.

2015 by American Society of Agronomy, Inc., Crop Science Society of America, Inc., and Soil Science Society of America, Inc.

All rights reserved. No part of this publication may be reproduced or transmitted without permission from the publishers.

The views expressed in this publication represent those of the individual Editors and Authors. These views do not necessarily reflect endorsement by the Publisher(s). In addition, trade names are sometimes mentioned in this publication. No endorsement of these products by the Publisher(s) is intended, nor is any criticism implied of similar products not mentioned.

ISBN: 978-0-89118-347-1

Library of Congress Control Number:
2015956808

Editor: Lisa Al-Amoodi
Designer: Patricia Scullion

Editor previous editions: Linda Deith
Designer previous editions: Susan Anderson

Printed in the USA.

Profitable forage production depends on high yields. Land, machinery, and most other operating costs stay the same whether harvesting 3 tons per acre or 6 tons per acre. Top yields in the northern United States have approached 10 tons per acre while average yields are around 3 tons per acre. This booklet describes what it takes to move from a 3-ton yield to 6 or 9 tons per acre.

A vigorously growing, dense stand of alfalfa forms the basis for profitable forage production. Profitable stands are the result of carefully selecting fields with well-drained soil, adding lime and nutrients if needed, selecting a good variety, and using appropriate planting practices to ensure germination and establishment.

Alfalfa requires a well-drained soil for optimum production. Wet soils create conditions suitable for diseases that may kill seedlings, reduce forage yield, and kill established plants. You can reduce some disease problems associated with poor drainage by selecting varieties with high levels of resistance and by using fungicides for establishment. Poor soil drainage also reduces the movement of soil oxygen to roots. Poor surface drainage can cause soil crusting and ponding which may cause poor soil aeration, micronutrient toxicity, or ice damage over winter. Even sloping fields may have low spots where water stands, making it difficult to maintain alfalfa stands.

Soils should be deep enough to have adequate water-holding capacity.

Alfalfa has a long taproot that penetrates more deeply into the soil than crops such as corn or wheat which have more fibrous, shallow roots. Under favorable conditions, alfalfa roots may penetrate over 20 feet deep. This great rooting depth gives alfalfa excellent drought tolerance.

Sloping fields where erosion is a problem may require use of erosion control practices such as planting with a companion crop or using reduced tillage to keep soil and seed in place until seedlings are well rooted.

Fields should be free of perennial weeds such as quackgrass. If not controlled before seeding, these weeds may re-establish faster than the new alfalfa seedlings and reduce stand density.

Weed management is discussed in more detail in the Production section.

Fields should be free from herbicide carryover that may affect growth of the new alfalfa and/or companion crop. This is especially important after drought years and on fields where high herbicide application rates or late-season applications of long-lasting herbicides were used.

Alfalfa plants produce toxins that can reduce germination and growth of new alfalfa seedings. This phenomenon is known as autotoxicity. The extent of the toxins influence increases with the age and density of the previous alfalfa stand when it was killed.

The autotoxic compounds are water soluble and are concentrated mainly in the leaves. The compounds impair development of the seedling taproot by causing the root tips to swell and by reducing the number of root hairs (). This limits the ability of the seedling to take up water and nutrients and increases the plants susceptibility to other stress factors.