Thursday, May 09, 2013
healthy_alfalfa_root_thumbnail_uc_extension

California Alfalfa: Too Much Water…. Bad News for Roots

AgFax.Com - Your Online Ag News Source


Many of us think about too much water killing alfalfa during the hot days of summer. And this does happen, especially at the tail end of fields where water may collect and stand for hours after the irrigation has ended.  When temperatures are over 100 oF and the soil is saturated for extended periods, roots can essentially suffocate due to lack of oxygen.

Plants die very quickly and roots begin to disintegrate. Because the root zone is usually saturated from the soil surface for a depth of several inches or even feet, the entire root rots. This situation is referred to as “scald” and is a physiological process rather than a pathology process.


There is another situation where saturated soil leads to dead alfalfa but in this case a fungus, called Phytophthora megasperma f. sp. medicaginis, is involved.  This soil-inhabiting fungus requires saturated soil conditions for infection to occur. Infected plants are most likely to be found in fields with clay soils, soils with poor drainage, long irrigation sets, or when any condition causes water to stand in the soil for a long time.

Sometimes the saturated soil condition is not obvious – the soil surface may be dry but, some distance below the surface, soil can be saturated due to soil type (heavy clay) or an impediment to drainage such as a hardpan. Because the disease requires saturated soils, Phytophthora-infected plants are often located at the tail end of a field but they can be found anywhere in a field when the right conditions occur.

While the “scald” mentioned in the first paragraph is only found in the high heat of summer, the optimum soil temperatures for infection by Phytophthora are 75-82 oF.  It is in the spring months (late March – May) that I have seen the highest levels of Phytophthora root rot.

This past April I saw a field with infected plants throughout the field. It was planted this past winter and the foliage was 6 to 12 inches high. Ten to fourteen days before I saw it, the field was flood irrigated. The heavy clay soil took water like a sponge – possibly a reflection of how dry the soil was due to the lack of rain this winter.

I could easily walk on the field but about 4-5 inches below the surface the soil was essentially mud.

Above ground, the plants on the levees were a nice green and had no symptoms (which is often the case when wet soil is contributing to alfalfa root problems). Between the borders, plants with tan-colored, dried leaves were scattered throughout the check, although they were more prevalent at the tail end.  Many plants were dead.

Beneath the soil surface, the portions of the roots that were in the upper part of the soil, where the soil was not saturated, appeared healthy (Photo 1) or at worst had small brown sunken spots (lesions) scattered on the roots (Photo 2).  Lower on the roots, where they were in contact with saturated soil, root tissue had died and was rotting.  On some infected plants, larger-than-normal lateral roots had developed on the healthy portion of the root above the rot (Photo 3).

Often laterals like these can compensate for the loss of the tap root but they will never grow vertically and as deep into the soil as a healthy tap root.  The result is a compromised root system and reduced production in summer because these plants can’t use water from lower in the soil profile when irrigations can’t keep up with crop requirements or are delayed due to harvest operations.

Photo 2. Small brown lesions of Phytophthora on alfalfa root.

Photo 2. Small brown lesions of Phytophthora on alfalfa root.

Photo 1. Relatively healthy root except for the rot at the root tip.

Photo 1. Relatively healthy root except for the rot at the root tip.

 

Photo 3. Lower tap root rotting but lateral rots are stronger.

Photo 3. Lower tap root rotting but lateral rots are stronger.

There is not a lot one can do once a field has Phytophthora root rot problems except to use good water management and and avoid saturating the soil.  Prevention before planting is the key. Plant alfalfa in fields with good drainage, rip or deep chisel prior to planting if necessary, provide a uniform and proper slope for the soil type and water delivery capacity, and select a variety with high Phytophthora root rot resistance to minimize the risk of this disease.

Tags: , , , , ,


Leave a Reply

Name and Email Address are required fields. Your email will not be published or shared with third parties.

Sunbelt Ag News

    Southern Grain: Freeze Effects? Corn Planting Slogs Along – AgFax4-19

    Rose On Cotton: Export Sales, Shipments Bear Watching4-18

    Arctic Warming Tied to Our Extreme Weather? Maybe. – DTN4-18

    Do Soybeans Need Nitrogen?4-18

    Is There An Advantage To More Corn Acres in Your Rotation? Yes and No.4-18

    Texas Rice: Garry McCauley Retires After 39 Years and Many Accomplishments4-18

    Keith Good: China’s Secret – Contaminated Farmland; Expect Drought Persistence4-18

    Rice Farmers In Midsouth Looking For A Break In The Weather – AgFax4-18

    Cleveland on Cotton: Nervous Market Nellies; Chinese Plant 20-25% Less4-17

    Grain TV: River Basis Levels See Large Rise4-17

    DTN Livestock Close: Meat Futures Take Wide Swings Before Exiting for Holiday4-17

    Doane Cotton Close: Heavy Volatility Continues in Old-Crop Prices4-17

    Chumrau on Wheat: World Supplies Get a Lift, but U.S. Stocks Look Tight4-17

    AFB Grain-Soybean Close: Wheat Higher, Corn Down, Beans Mixed4-17

    AFB Cotton Close: New-Crop Continues to Show Strength4-17

    AFB Rice Close: Across the Board Losses4-17

    DTN Cotton Close: Finishes Mixed Ahead of Long Weekend4-17

    Mississippi: MSU Offers Four Deer Management Workshops This Summer4-17

    Mapping the Farm Bill: Voting Changes in the House of Representatives4-17

    DTN Grain Close: Markets Mixed Ahead of Holiday Weekend4-17

    USDA: Peanut Price Highlights4-17

    Texas: Grain Grading Workshops, Amarillo, May 6-74-17

    Mississippi: State Soybean Value Grew $1B Since 20064-17

    U.S. Drought Outlook: Improvement Expected in Midwest, Central and Southern Great Plains4-17

    Farm Finances Rate an ‘A’ For Now, but Questions Linger — DTN4-17

    DTN Livestock Midday: Sharp Losses Hold in Cattle Trade4-17

    Mississippi: Top of the List for Water Resouces4-17

    DTN Grain Midday: Corn, Soybeans Move Lower4-17

    U.S. Grain Transportation: Upper Mississippi Navigation Improves4-17

    Resistant Palmer Pigweed: What People Need To Know Before It Hits – AgFax4-17

    Chemical Safety Board Plans Meeting in West, Texas — DTN4-17

    West, Texas, Recovers and Rebuilds with Cautious Approach — DTN4-17

    DTN Cotton Open: Trades Slightly Lower Nearby4-17

    U.S. Energy: Oil and Gas Spending Favors Exploration, Development4-17

    Gasoline Prices: Average Jumps 6 Cents4-17

    Propane Stocks: Increase by 0.8M Barrels4-17

    Diesel Prices: Average Down a Penny4-17

    DTN Livestock Open: Meat Contracts to Start Lower4-17

    Victims of Texas Fertilizer Plant Explosion Remembered — DTN4-17

    DTN Grain Open: Higher Start Led by Soybeans4-17

    Keith Good: Beige Book — Observations on Ag Economy4-17

    “Agricultural Adventure” Educate Public on Modern Farming – DTN4-16

    International Buying and Selling a Balancing Act to Get the Best Deal – DTN4-16

    Weather Woes Stretch from Iowa to Florida — DTN4-16

    Brazil’s Ports Remain Orderly with Good Luck, Favorable Conditions – DTN4-15

    Texas: Conservation Farming Meeting Weslaco, April 294-15

    Welch on Wheat: Cool Temperatures Hit Drought Stressed Crop4-15

    N.C. State University Leads Research into Kudzu Bug Host Preferences4-15

    Welch on Grain: Corn Planting in Line with 30 Year Average4-15

    Fertilizer Prices on the Rise but Still Lower Than Last Few Years4-15

    USDA: Weekly National Peanut Prices4-15

    Louisiana: Wildlife Field Day, Clinton, May 34-15

    Sign Ups Begin for USDA Disaster Assistance Programs4-15

    DTN Fertilizer Trends: Rail Delays Affecting Prices in Upper Midwest4-15

    Sunbelt Ag Events

     

    About Us

    AgFax.Com covers agricultural trends and production topics, with an emphasis on news about cotton, rice, peanuts, corn, soybeans, wheat and tree crops, including almonds, pecans, walnuts and pistachios.

      

    This site also serves as the on-line presence of electronic crop and pest reports published by AgFax Media LLC (formerly Looking South Communications).

        

    Click here to subscribe to our free reports.

      

    We provide early warnings and confirmations about pests, diseases and other factors that influence yield. Our goal is to quickly provide farmers and crop advisors with information needed to make better and more profitable decisions.

         

    Our free weekly crop and pest advisories include:

    • AgFax Midsouth Cotton, covering cotton production and news in Alabama, Arkansas, Louisiana, Mississippi, Tennessee and Missouri.

    • AgFax Southeast Cotton, covering cotton production and news in Alabama, Florida, Georgia, North Carolina, South Carolina and Virginia.

    • AgFax Southwest Cotton (new for 2013!), covering cotton production and news in Texas, Oklahoma, Kansas and New Mexico.

    • AgFax West (formerly MiteFax: SJV Cotton), covering California cotton, alfalfa, tomatoes and other non-permanent crops in California's Central Valley.

    • AgFax Rice covering rice production and news in Arkansas, Louisiana, Mississippi, Missouri and Texas.

    • AgFax Peanuts, covering peanut production in Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, Texas and Virginia.

    • AgFax Southern Grain: covering soybeans, corn, milo and small grains in Southern states.

    • AgFax Almonds, covering almonds, pistachios, walnuts and other tree crops in California's Central Valley.

    • AgCom 101, providing guidance to ag professionals involved in social media.

    Our newsletters are sponsored by the following companies: FMC Corporation Chemtura Dow AgroSciences.

          

    Mission statement:

    Make it as easy as possible for our community of readers to find and/or receive needed information.

              

    Contact Information:

    AgFax Media. LLC

    142 Westlake Drive Brandon, MS 39047

    601-992-9488 Office 601-992-3503 Fax

    Owen Taylor Debra L. Ferguson Laurie Courtney

          

    Circulation Questions?

    Contact Laurie Courtney