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

    Texas Cotton Industry Mourns The Death Of Economist Carl Anderson9-1

    Livestock: Market Lessons from 4-H County Fairs – DTN9-1

    China Cotton: Reserves’ Quantity, Quality Cause Problems – DTN9-1

    Welch on Wheat: Spring Wheat Harvest Running 22% Behind9-1

    Welch on Grain: Corn Condition Improves, Well Above Average9-1

    Keith Good: Production Costs Out of Balance with Expected Revenues9-1

    Flint on Crops: Rain Is Better Than Well Water9-1

    Chicago Board of Trade Closed Monday, Labor Day – September 18-29

    Rose on Cotton: Plenty of Gaps and No Rallies Expected8-29

    Peanut Harvest In N. Fla.; Drought Pushes Digging In Lower SE – AgFax8-29

    Rice Crop: Looking for a Normal Crop, Not a Bumper8-29

    Rice Market: Being Short Tricky but Being Long Takes Patience8-29

    Peanut Stocks and Processing: Utilization Up 2%, Stocks at 1.9B lbs8-29

    Cleveland on Cotton: Chinese Demand Pulling Prices Higher8-29

    DTN Livestock Close: Cattle Futures Sharply Higher on Positive Cash News8-29

    Doane Cotton Close: Futures Unable to Recover Losses8-29

    DTN Cotton Close: Late Rally Leaves Dec. Flat8-29

    AFB Grain-Soybean Close: Modest Losses Across the Board8-29

    AFB Cotton Close: Dec. Moves Fractionally Lower8-29

    AFB Rice Close: Futures Chart New Leg Down8-29

    Farm Bill: Cotton Transition Assistance Enrollment Now Open8-29

    Are USDA Corn Yield Forecasts Getting Better or Worse Over Time?8-29

    DTN Grain Close: Markets Settle Lower Ahead of 3 Day Weekend8-29

    USDA: Peanut Price Highlights8-29

    DTN Livestock Midday: Hog Futures Surge Higher8-29

    Farmers with Foreign Assets Face New IRS Rules and Serious Penalties8-29

    DTN Grain Midday: All 3 Markets Slide Lower8-29

    Mississippi Outdoors: Beaver Management Not a Simple Issue8-29

    Arkansas: Flood Damage to Crops Valued at $35.6M8-29

    Delta Soybean Yields Start Strong; Sugarcane Aphid Marches On – AgFax8-29

    California: Pinnacle Announces Acquisition of Kerman Ag Resources8-29

    DTN Cotton Open: Extends Prior-Session Loss8-29

    Midwest Farm Lenders Expect Solid Output; Lower Farm Income – Federal Reserve8-29

    Farm Payments to Stakeholders Rise as Gov. Payments Decline – USDA8-29

    Young Farmer in Your Future? – Helping Him or Her is Key to Success. – DTN8-29

    Net Farm Income Forecast to Fall,10.6% Decline Crop Value – USDA8-29

    DTN Livestock Open: Cattle Pits to Start with Mixed Prices8-29

    DTN Grain Open: Wheat Continues to Rally8-29

    Alabama: Pesticide Clean Days, Sept. 3-48-28

    Oklahoma: Fall Cotton Tour, Hydro, Sept. 118-28

    Rice Harvest Eases Into Gear In Midsouth – AgFax8-28

    Farm Drones Under Scrutiny: Farmers Impatient for FAA Ruling – DTN8-28

    USDA Readies Dairy Program, Producers Able to Sign Up Tuesday – DTN8-28

    U.S. Grain Transportation: Inspections Continue to Increase8-28

    Farm Program Decisions Hinge on Uncertain 2014 Crop Prices8-28

    Raindrops Keep Falling on Heads of Many Midwest Farmers — DTN8-28

    Economist: Big Potential in China for U.S. Corn, Livestock Exports8-28

    John Deere Lays Off 460 from Waterloo, Iowa Factory8-28

    U.S. Energy: Retail Gas Prices Follow Crude Prices Lower8-28

    Gasoline Prices: Decline by 2 Cents8-28

    Propane Stocks: Up to 74.7M Barrels8-28

    Diesel Prices: Average Drops a Penny8-28

    Sugarcane Aphid In Grain Sorghum: Florida, Georgia Find Infestations8-27

    Cotton – Midsouth – Bolls Opening, Early Defoliation Nears – AgFax8-27

    Midwest Corn and Soybeans Need Warm, Clear September – AgFax8-27

    Cotton – Southeast – More Open Bolls, Lingering Pests – AgFax8-27

    Farm Groups Map Waters to Block Clean Water Act Changes – DTN8-27

    Texas: 2 More Counties Make Natural Disaster List8-27

    Southwest May Face ‘Megadrought’ This Century, Say Scientists8-27

    China’s Citizenship Reform Should Benefit Farmers — DTN8-27

    What Can We Learn about Corn, Soybean Yields from Crop Tours?8-27

    Consider Sulfur for Your Fertility Plans This Fall — DTN8-27

    Rough Rice: Stocks Down 13 Percent from August 2013 — USDA8-27

    South Carolina: Peanut Field Day, Blackville, Sept. 48-27

    Cotton in Southwest – Early Yield Reports Good; Oklahoma Needs Rain – AgFax8-26

    Weather, Insects, Equipment Insurance, Health Issues – What Else? – DTN8-26

    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