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Kingfisher County OSU EXTENSION OFFICE

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Kingfisher Oklahoma         Armyworms Attacking Wheat

June 5, 2013

 

Roger Don Gribble

OCES NW Area Agronomist

 

Armyworm infestations are being observed in some parts of northwestern Oklahoma.  This caterpillar will measure about 1 and ¼ inches in length when mature and has a dark brown to grayish body with two pale yellow bands extending down the back.  The early signs of an infestation include leaves with ragged margins that have been chewed on.  You may also find “frass”, i.e. the excrement from the armyworm caterpillars, around the base of the wheat plant.  First observations need to around waterways, areas of lush growth, or areas with lodged wheat plants.  These are should be checked first to determine the size of the infestations in your fields.

Yield loss from armyworm feeding can occur in two ways.  First they can feed on the flag leaf and the awns which cause physiological yield loss because the grain head cannot fully mature and will usually shrivel the grain.  These worms can also cause direct yield loss by clipping the heads off the wheat stems.  Fortunately, head clipping is rare, but has occurred in northwestern Oklahoma.  The head clipping that I would normally see if we have heavy enough infestations is limited to secondary tillers with very small, green heads that would not likely contribute much to yield.

In general, if wheat is past the soft dough stage, control of the caterpillars is not warranted unless obvious head clipping can be seen and the caterpillars are still present and continuing to feed.  Worms feeding on the awns when plants are past the soft dough stage of growth will not cause enough yield loss to justify the expense of a plant protection application.

To scout for armyworms, select several locations and search the ground and plant material for armyworms.  The caterpillars tend to feed at night, so a good strategy is to bring a flashlight and look at the fields after dusk when they are feeding. 

Armyworms have a number of natural enemies that help keep populations in check, if given a chance.  In particular, parasitic wasps and flies will attach them.  Parasitized armyworms can often be recognized by the presence of small white eggs attached behind the caterpillar’s neck.  The eggs are about the size of a period at the end of each sentence in this article!

 

The suggested thresholds for armyworms are 4-5 unparasitized caterpillars per foot of row.  If control is needed, there are a number of products registered for use.  A producer must consider at this time the harvest restriction period that must be observed prior to harvest.  Your OCES Ag Educator, located in each county in northwestern Oklahoma has OCES Extension Fact Sheet CR-7194, Management of Insects and Mite Pests in Small Grains, available for you at your request!

Oklahoma State University, U.S. Department of Agriculture, State and Local Governments cooperating.  Oklahoma Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, sex, age, status as a veteran, or disability and is an Equal Opportunity Employer.

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