Agricultural/Livestock Information

Alfalfa Weevil Management

   Tim Schnakenberg, MU Extension Field Specialist in Agronomy, Galena, MO

   Anthony Ohmes, MU Extension Field Specialist in Agronomy, Jackson, MO

   Sarah Kenyon, PhD, MU Extension Field Specialist in Agronomy, West Plains, MO

1.       Understand the weevil life cycle and damage it causes.  Adult weevils often lay eggs inside alfalfa stems during warm days in the fall, winter, and spring.  Alfalfa weevil larvae grow through four stages (instars).  Alfalfa weevil egg hatch and instar development begins when temperatures are above 48?F.  Early in the season the first and second instars feed inside the terminal leaves, and show up as pinhole feeding.  When the third and fourth instars develop they move to foliage on the lower portion of the plant, at this stage a large amount of foliage can be consumed.

 

2.       Scout often starting early in the spring.  Walk alfalfa fields as early as late March for signs of leaf feeding.  Most years the feeding gets progressively worse through April.  The most effective scouting technique is to collect ten alfalfa stems in each of five locations around the field and tap them into a white bucket.  Be sure to gently handle the stems so larvae don’t fall to the ground before getting them to the bucket.  Scissors can be helpful to accomplish this.  Determine the average number of larvae per stem.  The economic threshold for alfalfa weevils is an average of one or more larvae per stem and 30 percent or more of the plant terminals show feeding damage.  If the field’s infestation is greater than this, it may be time to start spraying. 

 

In cool, wet springs, a fungal pathogen called Zoophthora phytonomi can infect and kill weevils.  If this occurs, the infected larvae turn from their normal green color to a yellow color and may die off in 2-3 days after infection occurs.

 

Using degree day information to schedule field checks may save time.  Information about degree days can be found at Missouri Commercial Agriculture Weekly Weather Station Summary http://agebb.missouri.edu/weather/reports/gddTable.asp

 

Alfalfa weevil feeding can be observed after a buildup of 190 degree days following a mild winter.  In most years damage occurs later and scouting should begin after 225 degree days.  More information about degree days and alfalfa weevil thresholds can be found at https://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1335&context=ky_alfalfa    

 

3.       Decide if early harvest is necessary.  Early harvest, by either machine or livestock, is an option for management of weevils.  This removes food and shelter from larvae and also increases their exposure to the sun.  Remember, that it is best for the crop to not harvest earlier than 7-10 days prior to the normal growth stage of 1/10th bloom.  Missouri research has found that 98% of the weevils can be reduced with mechanical harvest and 90% can be reduced by grazing cattle.  If grazing, be cautious of bloat from wet foliage and damage to the crowns from trampling during wet conditions.

 

4.       Choose labeled insecticides if threshold levels are reached.  Factors that may reduce efficacy of insecticide applications when used to control alfalfa weevil larva include:

 

a.       Cool Temperatures.  Temperatures below 60?F slow the metabolic process of the developing larvae and often slow the onset of larval mortality below what is normally expected when insecticides are applied at warmer temperatures.  Steward insecticide (Indoxacarb) has demonstrated increase larval mortality when used in cool conditions.  Although, when conditions are normal insecticide efficacies on alfalfa weevil larvae are generally equivalent.

b.       Insecticide rate. Use of lower rates of insecticides when larval populations are very high may lead to reduced efficacy.  Make sure to read the insecticide label to determine the correct rate.

c.        Poor coverage.  It’s best to use a lot of water in the spray mix for ground applications, with 20 gallons per acre considered optimum, and proper tip selection.

d.       Pesticide resistance.  Development of resistance to the pesticides being used can decrease insecticide efficacy.  To avoid pesticide resistance, rotate mode of action being used. 

Be sure to read and follow label directions, precautions, and restrictions of the product you purchase.      

FOR IMMEDIATE RELEASE

Contact:        Patrick Davis

                        Regional Livestock Field Specialist

                        MU Extension

                        417-276-3313

                        davismp@missouri.edu

 

Date:              Wednesday, March 13, 2019

Headline:  Add legumes to fescue pastures for better profits

STOCKTON, Mo. - Cattle producers see more profit when they add legumes to fescue pastures and manage grazing systems properly, says Patrick Davis, University of Missouri Extension specialist in livestock.

Fescue remains the hardy mainstay of southwest Missouri pastures. Adding legumes gives fescue fields more nutritional punch and profit.

Davis says proper management is key to making grasses and legumes work well together. This begins with a management intensive grazing system (MIG).

Under MIG, cattle graze on forage between 3 to 8 inches tall. Cattle begin grazing at 8 inches and eat forage to 3 inches followed by paddock rest until the forage reaches original height. This strategy promotes stronger roots and cattle graze best quality forage. Forage in this range also contains less ergovaline, a toxic ergot alkaloid.  The highest concentrations of ergovaline are in the bottom two inches of the plant and seed heads.

Add legumes into fescue pastures for other benefits. Pasture quality improves and the amount of toxic fescue is diluted when mixed.

“Proper incorporation and management of legume species, including red and white clover, or lespedeza is important for their persistence into your fescue sod,” says Davis.

Two seeding options are frost seeding or no-till drilling. Contact your local MU Extension agronomy field specialist for advice on seeding methods or download MU Guide G4652 from https://extension2.missouri.edu/g4652.

To persist, legumes need time to grow without fescue competition and time to delay grazing pressure.  Proper MIG allows both, says Davis.  After grazing, allow a 4 to 5 – week rest period for young legume plants to improve chances of persistence. 

Before planting, test soil.  Make sure soil pH is greater than 6.0 for red and white clover and over 5.5 for lespedeza plantings.  The local MU Extension Center and agronomy field specialist can advise on proper soil testing procedures and fertility for growing these legumes.

“Legumes are higher quality than grasses because of the lower stem to leaf ratio.  This results in lower neutral detergent fiber and increased protein concentrations.  This combination improves forage intake, cattle performance and operation profit potential,” says Davis.

Total pasture legume coverage should be approximately 30%.  If coverage is above 50% then cattle bloat potential increases.

Davis gives these tips to reduce cattle bloat potential:

·         Restrict grazing and allow cattle time to adapt to the legume field

·         Provide cattle dry hay before turning them out to legume pasture to reduce legume intake

·         Provide poloxalene to cattle through bloat blocks or other ways of supplementation

Contact the MU Extension livestock or agronomy field specialist in your area for more information.  You may also find more information on how to improve your grasslands at https://extension2.missouri.edu/programs/nrcs-mu-grasslands-project

 

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