Disc or Spray Your Wheat Infested With Hessian Fly?

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I have received many calls from agents and farmers from across the east about Hessian fly. An alert was sent out in late December last year about heavy egg lay from the warm December weather. Because of that warm weather, we cranked out an extra generation of flies this year (see graph below). So larvae and pupae you are seeing now are probably from that December generation. Dr. Randy Weisz, former NCSU wheat agronomist, posted posted a short (2 minute video) during 2014 about these Hessian Fly infestations and control options that is still good information. More information below on should you disc or spray wheat infested with Hessian fly.

Hessian fly eggs at Kinston, NC in plots with and without treated seed and with and without insecticide sprays every other week.

Hessian fly eggs at Kinston, NC in plots with and without treated seed and with and without insecticide sprays every other week. Information and graph from Forrest Howell, NSCU Entomology MS student.

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) A thin stand planted to a susceptible variety and Hessian fly present.  Research from our state has shown that these fields will not benefit from a spring foliar spray and additional nitrogen. No more tillers can be made at this point and Hessian fly larvae present now have the potential to kill even more tillers. Also consider that this generation will develop, reinfest, and can kill more tillers or cause grain heads to lodge. Disc this field up.

2) A thick or moderate stand planted to a susceptible variety with a light Hessian fly infestation. Leave this field alone. You might benefit from thinning a few tillers due to Hessian fly. Spring infestations are not as severe as those in the fall.

3) A thick or moderate stand planted to a susceptible variety with a heavy Hessian fly infestation. These fields might benefit from a spring spray, although there is little data to support this. If you absolutely must do something, timing will be critical. There are few problems tank mixing insecticides with nitrogen, but you need to decide whether you want to time the spray for the wheat (N portion) or the fly (insecticide portion). These don’t often overlap and will have little impact on cereal leaf beetle or stink bugs if they are put on in March.

From the fly perspective, try to time the spray with warm weather. 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

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.