Should you Spray Wheat for Hessian Fly?

I have received many calls from agents and farmers from across the east about Hessian fly.  Dr. Randy Weisz just posted posted a short (2 minute) video alert about these Hessian Fly infestations and control options.  Historically, most our Hessian fly issues have been centered in the far eastern counties, not only because of rotations (continuous wheat after beans), but I think because these areas have a unique climate from much of the rest of the state.  As a result, I’m not too surprised to hear of these issues, but the damage has extended this year into areas of the Coastal Plain that are usually spared from Hessian fly.

Remember how wet last summer was?  Stupid question.  Some wheat was never harvested or was harvested late.  We also had abundant summer rain that could have germinated some volunteer wheat in soybeans planted behind wheat.  These conditions created abundant oversummering habitat for the fly, resulting in fall infestations.  We are noticing these now since our wheat is picking up.  This damage is already done, but what can we do to prevent damage from spring infestations?

Hessian fly pupa.

Hessian fly pupa.

First, it is important to scout your wheat to determine if symptoms you are seeing (yellowing, lack of vigorous growth, poor tillering, etc.) is a result of Hessian fly or something else.  Other causal agents of these symptoms could include things like cold weather, lack of nitrogen, and wetness.  Hessian fly are present as pupae in the fields at this time of the year.  To scout for pupae, carefully dig up tillers below the soil and peel back the outer layers of leaves.  Often pupae will fall out into the soil or will be feeding on the base of the plant behind these leaves.

Once you have determined the presence of Hessian fly, you need to make a decision about what to do with your field.  Our resistant varieties are still holding up well, so you should focus on fields that are planted with a susceptible variety (listed here).  Then separate your fields with susceptible varieties into three categories independent of planting date.

1) Fields that have some Hessian fly from the fall generation and are planted with a susceptible variety.  Research from our state has shown that these fields will not benefit from a spring foliar spray.  All fields with a susceptible variety likely have Hessian fly at some level.  The vast majority of fields in our state fall into this category.

Pheromone traps were used for these data and only catch males.  Note that 2010-2011 was a cold winter, so these results will not apply to every situation.  However, this graphs shows that we generally see a peak of adult fly activity in late-fall, followed by a peak in late-winter and early-spring.

Pheromone traps were used for these data and only catch males. Note that 2010-2011 was a cold winter, so these results will not apply to every situation. However, this graphs shows that we generally see a peak of adult fly activity in late-fall, followed by a peak in late-winter and early-spring.

2) Fields that are moderately infested with Hessian fly from the fall generation and are planted with a susceptible variety.  These fields may benefit from a spring foliar spray, but timing will be critical.  Try to time the spray for warm weather we are experiencing in late March.  You can improve your chances for spray effectiveness by looking at the progression of pupae development.  When you squeeze them and they begin to pop pink or red, instead of white, they are close to becoming adults.  Remember that we are timing the spray to kill adults, so you should try to hold off your spray until most of the pupae are developed or some have emerged.  The cutoff for this category (heavily infested) and the previous category might be somewhere around 50% infested tillers from the fall generation.

Eggs per 10 leaves on 20 March and number of Hessian fly larvae per 5 plants on 6 April in a 2001 spring rescue spray trial done by Dr. John Van Duyn,

Eggs per 10 leaves on 20 March and number of Hessian fly larvae per 5 plants on 6 April in a 2001 spring rescue spray trial done by Dr. John Van Duyn,

7 DAT

3) Fields that are severely infested with Hessian fly from the fall generation and are planted with a susceptible variety.  Unfortunately the best option for some fields will be to till them up.  Fields approaching a 100% rate of infested tillers with plants that are dying or dead will fall into this category.  I would not waste spraying a field that did not tiller well in the fall and was set back by Hessian fly and cold wet weather.

Susceptible variety of wheat devastated by fall-generation Hessian fly.  This field is a complete loss and will not benefit from a rescue spray in the spring.

Susceptible variety of wheat devastated by fall-generation Hessian fly. This field is a complete loss and will not benefit from a rescue spray in the spring.

Dead and dying plants resulting from fall-generation Hessian fly.  These plants will not recover.

Dead and dying plants resulting from fall-generation Hessian fly. These plants will not recover.

More information on Hessian fly can be found on this video. (Hessian Fly Management).  Finally, you can link to a web version of “Biology and Management of Hessian Fly in the Southeast” here and can download a .pdf with interactive links to web-based data here.

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Written By

Dr. Dominic ReisigAssociate Professor and Extension Specialist (252) 793-4428 Entomology - NC State University

Posted on Mar 12, 2014

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