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

    USDA Commentary: Weekly Cotton Markets, Weather by Region7-25

    Rose on Cotton: No Pleasure in this Market Made for Bears7-25

    Rice Market: U.S. Futures Decline as Global Prices Rise7-25

    Rice Crop: Harvest Begins Slowly in Louisiana and Texas7-25

    Rice Commentary – Rice Farmers Need to Consider a New Business Plan7-25

    Leave Your Guns at the House, Boys.7-25

    DTN Livestock Close: Cattle Futures Explode to New Highs7-25

    Doane Cotton Close: Futures Continue Lower After Midweek Rally7-25

    AFB Grain-Soybean Close: Soybeans Mixed, Wheat, Corn Gain Slightly7-25

    AFB Cotton Close: Sell-Off Continues7-25

    AFB Rice Close: Futures Continue Lower7-25

    DTN Cotton Close: Settles on New Contract Lows7-25

    Peanuts: 15% Of Crop Ungathered In Key Argentine Production Area7-25

    Rail Car Delays Causing Dread Among Elevator Operators – DTN7-25

    DTN Grain Close: Wheat Prices Rally Off Lows7-25

    Catfish Production: Water Surface Acres at 63,700 Acres7-25

    USDA: Peanut Price Highlights7-25

    Arkansas: New iPhone App Simplifies Farmers’ Finances7-25

    DTN Livestock Midday: Cattle Futures Continue Higher7-25

    DTN Grain Midday: Wheat 3 to 6 Cents Up in Front Months7-25

    Taking the Risk Out of Buying Used Equipment — DTN7-25

    North Carolina: Rediscovering Grain Sorghum — DTN7-25

    Peanuts: Worms Still Building In SE; Rains Boost West’s Crop – AgFax7-25

    Shurley on Cotton: Prices Try to Stabilize, Still Show Weakness7-25

    Southern Soybean Insect Situation Gets Complicated – AgFax7-25

    DTN Cotton Open: Extends Losses in Early Going7-25

    AgFax Wildlife Review: Wild Hogs Damaging Levees in Louisiana7-25

    DTN Livestock Open: Cattle Futures Likely to Begin Mixed7-25

    DTN Grain Open: Soybeans, Corn Starting Out Lower7-25

    Keith Good: Declining Commodity Prices Foreshadow Ag Slump? Maybe.7-25

    Ethanol: Final 2014 RFS Release ‘Imminent’ – DTN7-24

    Doane Cotton Close: Prices Break Out of Range Lower7-24

    Rice – Arkansas, Mississippi – Blast Becomes Major Concern – AgFax7-24

    New Rural Infrastructure Fund Established — DTN7-24

    U.S. Grain Transportation: Wheat Demand Increases, Inspections Rise7-24

    2014 Farm Bill Decisions: Base Acre Reallocation Option7-24

    Midwest Grain: Pull the Fungicide Trigger Now? It Depends. – AgFax7-24

    Louisiana: Sodium Nitrite Explored for Wild Hog Control7-24

    U.S. Energy: Refineries Running at Record Levels7-24

    Gasoline Prices: Show 4-Cent Decrease7-24

    Propane Stocks: Continue to Rise7-24

    Diesel Prices: Average Declines by 3 Cents7-24

    Corn: Pollination is One of Nature’s Miracle – DTN7-23

    Wheat Tour Sees One of the Best Crops in Years – DTN7-23

    10 Arkansas and 2 Tennessee Counties Designated Natural Disaster Areas7-23

    Soybeans: Is the 2014 Average Yield Headed for a New Record?7-23

    Drones Monitoring the Garden or Your Crop? One Is Legal, One Is Not.7-23

    Cotton In The Midsouth – Plant Bugs Persist As Bollworms Arrive – AgFax7-23

    Cotton – Plant Bugs, Stink Bugs Overlapping In Parts Of Southeast – AgFax7-23

    Cotton in Southwest: Blooms Spreading; Fleahopper, White Fly on the Move7-22

    USDA: Don’t Forget Farm Bill Conservation Compliance Changes7-22

    USDA: Weekly National Peanut Prices7-22

    Good Reports on Corn; Wet Weather Stressing Beans — DTN7-22

    Cattle: Nebraska Study Finds No Ill Effects from Zilmax — DTN7-22

    South Korea Importers Returning to U.S. Corn, DDGS — DTN7-22

    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