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

    AgFax Grain Review: Syngenta Lawsuits Pile Up; GMO Seed Companies Sue Hawaii11-21

    Rose on Cotton: Looking for the Positives This Week11-21

    Grain Drying: What Happens After Sudden Temperature Drop?11-21

    Is Your Lifestyle Costing You the Farm?11-21

    Grain TV: Lower Barge Rates Boost Basis Levels11-21

    DTN Livestock Close: Cattle Futures Solidly Higher11-21

    Farmers Storing Grain Need to Weigh Risk Management Factors – DTN11-21

    Peanut Harvest Updates From Southeast, Delta And Southwest – AgFax11-21

    Cleveland on Cotton: 57 Cents – ‘The Bottom is In’11-21

    Ag Labor: Immigration Order Provides Little Long-Term Benefit – DTN11-21

    Doane Cotton Close: Decline in Chinese Production Offers Support11-21

    AFB Grain-Soybean Close: Strong Soybean Gains, Little Movement in Corn, Wheat11-21

    Southern Soybean, Corn Harvest Reports, Round One – AgFax11-21

    AFB Cotton Close: Futures Rebound11-21

    AFB Rice Close: Prices See More Slight Gains11-21

    DTN Cotton Close: Settles Higher on Light Volume11-21

    DTN Grain Close: Soybeans Boosted by Demand11-21

    USDA: Peanut Price Highlights11-21

    Oklahoma Pecans: Deliveries Remain Light11-21

    Georgia Pecans: Buying Interest Very Active11-21

    Ag Policy: Farm Bills Need Long-Term View11-21

    Cotton Market Weekly Review by Region11-21

    DTN Livestock Midday: Cattle Futures Surge Higher11-21

    A Closer Look at Impacts of Olympic Averaging of Prices and Yields11-21

    Arkansas Cattle: Ranchers Should be Alert to Acorn Poisoning11-21

    DTN Grain Midday: All 3 Commodities Go Higher11-21

    Economist: Livestock Industry Will Have Strong Rebound11-21

    DTN Dried Distillers Grain: Cheaper Feed Source for Beef Producers?11-21

    Mississippi Outdoors: Common Deer Parasites Do Not Affect Venison11-21

    DTN Cotton Open: Trades Higher after No Notices Issued11-21

    AgFax Wildlife Review: New E-Book Offers Tips for Gardening in South11-21

    DTN Livestock Open: Cattle Futures to Start Mixed11-21

    Weather Challenges Florida and Iowa Farms — DTN11-21

    Vilsack: Immigration Order Creates ‘Stability’ in Ag Work Force — DTN11-21

    DTN Grain Open: Lower Start Across Board11-21

    Keith Good: What’s Next for Meat Labeling?; Sugar Prices Take Tumble11-21

    Texas Cotton Harvest – Still Some To Go – AgFax11-20

    Mississippi: Water Conservation Summit, Stoneville, Dec. 1011-20

    Farm Internet Service Still Slow or Non-Existent, But Improving – DTN11-20

    Yield: Important Factor in Your Irrevocable Farm Program Choice11-20

    U.S. Grain Transportation: Weekly Inspections Reach Record11-20

    U.S. Drought Outlook: Improvements Expected for California, Southwest11-20

    U.S. Energy: Planned Refinery Maintenance Light in 201411-20

    Propane Stocks: Post Slight Increase11-20

    Gasoline Prices: Decrease by 5 Cents11-20

    Diesel Prices: Average Drops 2 Cents11-20

    Livestock: Arctic Chill Catches Markets Flatfooted – DTN11-19

    Farm Runoff Targeted for Regulation Following Algal Bloom Shutdown – DTN11-19

    Soybeans: China May Import More Non-GMO Beans – DTN11-19

    Mississippi Outdoors: Free Apps Can Aid Deer Hunters11-19

    Big River Rice And Grain Enhances, Expands Facilities In Arkansas, Louisiana11-19

    Farm Bill Commodity Program: Decisions and More Decisions11-18

    Young Farmers: USDA is the ‘Lender of 1st Opportunity’ – DTN11-18

    Tax Extenders: Farm Groups Push Congress to Renew Section 179 This Year – DTN11-18

    AgFax Rice Review: Iraq Passes on U.S. Rice; Australia, China Sign FTA11-18

    USDA: Weekly National Peanut Prices11-18

    DTN Fertilizer Trends: Prices Show Little Movement11-18

    North Carolina: Bt Resistant Armyworms Migrating North11-18

    Georgia Cotton Commission Meeting, Production Workshop, Tifton, Jan. 2811-18

    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