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

    Rose on Cotton: We told you. Old Crop is Too Cheap.4-24

    GMOs – Why Some People Lose Reason About The Technology4-24

    Dow’s Enlist Weed Control – How the System Works4-24

    Grain TV: Brazil Trucker Strike Flares Up Slightly4-24

    Rice Progress: Wet Weather Issues, Planting Delays and Flooded Fields4-24

    DTN Livestock Close: Aggressive Short Covering4-24

    Rice Market: Overbearing Carryover Strain Continues4-24

    New Technology: Can it Help You Cut Costs? Consultants Talk About It. – AgFax Midwest Grain4-24

    Southern Corn Crop – Plenty Of Acreage Still In The Sack – AgFax4-24

    AFB Grain-Soybean Close: Weather Pulls the Rug Under Prices4-24

    AFB Cotton Close: Strong Exports a Boon to Prices4-24

    AFB Rice Close: Exports Unable to Spark Buying4-24

    DTN Grain Close: Favorable Weather Easing Concerns4-24

    Monsanto, Pioneer Genetically Modified Traits Approved by EU – DTN4-24

    USDA: Peanut Price Highlights4-24

    China’s Ag Production: More Corn, Wheat, Rice, Cotton, Less Soybeans4-24

    John Deere: Your Tractor But Not Your Software – DTN4-24

    Dried Distillers Grain: Salt Supplements Save Pasture Grass – DTN4-24

    DTN Livestock Midday: Limited Trade Volume4-24

    Texas: Wheat Field Day, Chillicothe, May 134-24

    Weekly Cotton Market Review – USDA4-24

    DTN Grain Midday: Demand Concerns Promote Selling4-24

    DTN Cotton Open: Cash Grower Sales Resume4-24

    FMC Corporation Completes Acquisition of Cheminova4-24

    Indiana: No-Till and Cover Crops – A Farmer’s View – Video4-24

    DTN Livestock Open: Support from Spillover Buying4-24

    DTN Grain Open: Soybeans Fail to Hold Near Session Highs4-24

    USDA Plan to Lower Greenhouse Gases is a ‘Very Big Deal’ – DTN4-23

    Biofuels: Senators Urge for RFS to Continue Industry Growth – DTN4-23

    U.S. Drought Monitor Quick Look Video – AgFax4-23

    ELS Cotton Competitive Payment Rate Is Zero4-23

    DTN Cotton Close: Strong Exports, Heavy Trade4-23

    Chumrau on Wheat: Competitive Factors Pressuring U.S. Export Pace4-23

    Moving Grains: Barge Rates Down on Improving River Conditions4-23

    U.S. Drought Monitor: Strong Rains in Southeast, Great Plains4-23

    Good on Grain: Spring Wheat Yield Expectations – What Does History Teach Us?4-23

    Alfalfa: From Bone Dry to Fairly Decent Moisture – DTN4-23

    Cutworm Moths on the Move, Don’t Bet on BT Hybrids or Seed Treatments – DTN4-23

    California Oat Hay: Barley Yellow Dwarf Virus Hits Hard, Some Varieties More Tolerant4-23

    Bird Flu: Poultry Produces Watch for Symptoms, CDC Says – DTN4-23

    Irrigation Systems: Are All Your Systems Go?4-23

    Grain TV: Traders Eye Cold Weather in the Midwest4-22

    Residential Propane, Heating Oil: Inventories Increase4-22

    Diesel: Prices Increase Across U.S.4-22

    Gasoline: Average Price Up from Last Week4-22

    U.S. Energy: May Tight Oil Production Expected to be Lower than April’s4-22

    Weed Management: A Regional Approach – Farmdoc4-22

    3 Things to Know About the Current Highly Pathogenic Bird Flu Outbreaks – USDA4-22

    Utah: 2 Counties Declared Natural Disaster Areas Due to Drought – USDA4-22

    Oregon: 4 Counties Declared Natural Disaster Areas Due to Drought – USDA4-22

    USDA’s Hands Tied on Cuban Trade Promotion – DTN4-22

    Soybeans: 5 Million Bushles Ending Stocks Not Helping Prices – Rabobank4-22

    Tree Nuts: U.S. Exports to China Are Down, Prices Remain High – Rabobank4-22

    Corn Market: Next Big Price Factor is Spring Planting – Rabobank4-22

    Fertilizer Market: Prices Decline; Growers Using Less to Do More – Rabobank4-22

    Rice Market: CA Growers Expect Water Cuts; Southern Acreage May Increase – Rabobank4-22

    Cotton Market: Neutral on Old Crop, Bullish New Crop – Rabobank4-22

    Pest Management: 9 Facts Concerning Black Cutworms Popping Up in the Midwest4-22

    Indiana and Nebraska: Weather Challenges are Like Water Off a Duck’s Back to Seasoned Farmers – DTN4-22

    Wheat: Efficacy of Fungicides, Timing Matters4-22

    Herbicide Resistance: Tank Mixing the Key to Control – DTN4-21

    Illinois Corn: Projected Revenues for 2015 – Farmdoc4-21

    Soil Health: Testing Ideas – Are They Worth the Money? – DTN4-21

    Sweet Potatoes Could be an Example of Natural GMOs4-21

    Drought: New Stress Detecting Sensors Help Manage Water Use4-21

    Kentucky: Cover Crop Burndown Tips; Worms and Weevils on the Rise4-21

    USDA: Weekly National Peanut Prices4-21

    Herbicide Resistance: Slowing Weed Evolution with Management Practices4-21

    Grain Sales Direct To Buyer? AgriCharts Rolls Out A Platform.4-21

    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

    Owen Taylor Debra L. Ferguson Laurie Courtney

          

    Circulation Questions?

    Contact Laurie Courtney +