Wednesday, May 09, 2012

Iowa: Start Scouting for Stalk Borer in Corn

AgFax.Com - Your Online Ag News Source


Iowa has been steadily accumulating degree days ahead of schedule in 2012. Over the weekend, some parts of southern Iowa hit an important degree day benchmark for common stalk borer.

About 10 percent of stalk borer larvae can begin moving to corn after accumulating 1,300 to 1,400 degree days. Part of southwestern and southeastern Iowa have reached that threshold and we recommend starting to scout this week in corn (Fig. 1). Central and northern Iowa should start scouting May 12 to May 18, if warm temperatures continue. This is about three weeks earlier than last year.


Figure 1. Growing degree days accumulated (base 41°F) for stalk borer larval movement in Iowa for 2012. Begin scouting around 1,300 to 1,400 degree days. Map courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy.

 

Stalk borer eggs are laid on grasses and weeds in the fall, and young larvae will feed in the spring until they outgrow the plant. Corn can become infested when stalk borer larvae move to find bigger host plants, typically adjacent to grassy edges of emerging corn. The most susceptible stages of infestation are at V1-V5, or about 2 to 24 inches in plant height. Larvae can damage corn by defoliating leaves and burrowing into stalks. Stalk borers do not typically cause economic damage when feeding on the leaves, but can clip newly emerging plants and cause death (Fig. 2). More often, larvae kill corn plants by entering the stalk and destroying the growing point (i.e., flagging or dead heart). A dead heart plant will have outer leaves that appear healthy, but the newest whorl leaves die and can cause barren plants.


Figure 2. Stalk borer can shred corn leaves and destroy the growing point.

Stalk borer infestations are more likely in corn surrounded by giant ragweed. Female moths prefer to lay eggs in weedy areas in August and September, so minimizing weeds in and around corn during that time will discourage egg-laying. Using herbicides to kill spring weeds can force stalk borer larvae to infest young corn plants. Long term management requires controlling grassy edges around corn so that mated females will not lay eggs in that area during the fall.



Fields with persistent stalk borer infestations should be monitored every year. Applying insecticides to infested corn is not effective because the larvae are protected once tunneled into the stalk. Instead, target foliar applications to larvae as they migrate from grasses to corn. Look for larvae inside the whorls to determine the number of plants infested. The larvae are not highly mobile and typically only move into the first four to six rows of corn. Look for new leaves with irregular feeding holes or for small larvae resting inside the corn whorls. Larvae will excrete a considerable amount of frass pellets in the whorl or at the entry hole in the stalk. Young corn is particularly vulnerable to severe damage, but plants are unlikely to be killed once reaching V7 (seven true leaves).

Control

To prevent stand loss, scout and determine the percent of infested plants. The use of an economic threshold (Table 1), first developed by ISU entomologist Larry Pedigo, will help determine justifiable insecticide treatments based on market value and plant stage. Young plants have a lower threshold because they are more easily killed by stalk borer larvae.


Table 1. Economic thresholds for stalk borer in corn, based on plant stage, expected yield and market value.

If an insecticide is warranted, some products can be tank-mixed with a fast burndown herbicide, or applied seven days after a slow burndown herbicide. Border treatments should be considered if infestations are localized. Insecticides must be well-timed so that products are reaching exposed larvae before they burrow into the stalk. Make sure to read the label and follow directions, especially if tank-mixing with a herbicide, for optimal stalk borer control.

Life cycle

There is just one generation per year in Iowa, and the egg is the overwintering stage. Like all insects, stalk borers develop based on temperature. Egg hatch typically occurs around April 19 to June 5, or 50 percent egg hatch happens at 494 growing degree days. The number of larval molts is variable depending on food quality, and ranges from seven to nine instars. Fully developed larvae drop to the soil to pupate. Approximately 50 percent of pupation happens at 2,746 growing degree days, with 50 percent adult emergence at 3,537 growing degree days. Peak adult flight occurs during the first two weeks of September.

Description

Stalk borer larvae have three pairs of true legs and four pairs of fleshy prolegs. The body is creamy white and dark purple with brown stripes. Often there is a creamy white stripe running down the back. A distinctive feature is an orange head with two dark lateral stripes (Fig. 3). The adults are dark gray and brown colored moths, with jagged white lines and two to three clusters of white spots.


Figure 3. Stalk borer larva. Photo credit Marlin E. Rice.

For more information on stalk borer biology and management, read a recent Journal of Integrated Pest Management article by Rice and Davis (2010), called “Stalk borer ecology and IPM in corn.”

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