Insecticide Seed Treatments and Sprays for Hessian Fly
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Chances are you’ve already made the decision about whether to include an insecticidal seed treatment. Now it’s important to know what you can expect out of it. This article will cover insecticidal seed treatments first and then sprays for Hessian fly. If you want more extensive coverage of all our recommendations and fly biology, they can be found in Biology and Management of Hessian Fly in the Southeast, the Small Grain Production Guide, or this video. Also, there is no fly-free plant date in North Carolina. Flies are active anytime we have enough warm days in a row throughout the fall, winter and spring. That being said, there are fewer flies in the colder months and later plantings are less at risk.
Insecticidal seed treatments
1) Varietal susceptibility is the key to Hessian fly management. The more you make a seed treatment do the heavy lifting over top a susceptible variety, the more failure you can expect. See a list of high yielding varieties with Hessian fly resistance ratings (if known). We can also lump other factors into this category. If you no-till, plant near last year’s soybeans double cropped behind wheat, plant earlier than the recommended planting window, etc., you will be putting more pressure on your seed treatment.
2) Rates make a huge difference. We did extensive testing with an insecticidal seed treatment in 2010 and 2011. Higher rates worked well to kill Hessian fly. Both Cruiser and Gaucho work seemed to work well at the highest labeled rates. Some insecticidal seed treatment rates are not labeled high enough for good Hessian fly control. Be sure you know what rate you are getting from your dealer as there is a labeled range for Hessian fly. Scott Stewart, U. of Tennessee, has an excellent recent article about this from the perspective of aphids.
1) You need to meet the following four conditions to make a spray pay: 1) planted wheat early (during October); 2) have historical pressure; 3) planted a susceptible variety (see list); 4) have not used an insecticidal seed treatment and are not past the 2 leaf stage. The best time to spray is when eggs are first present, but these are difficult to see and the timing of flights varies with weather. Some consultants and scouts are trained to find them, but I’m not sure that even then we would do much good with our sprays since they are timed at adults. Could you find the Hessian fly egg in the photo?
2) Time your spray correctly. If you wait to spray beyond the two leaf stage and you have damaging levels Hessian fly, you’ve lost yield. The graph below demonstrates the effect of seed treatments and insecticidal sprays on Hessian fly eggs. The first spray was initiated 3-4 weeks following planting. Sprays did not reduce the number of eggs. Spray timing is critical for success. The earlier the spray, the better it will work.
3) You will get more bang for your buck out of a seed treatment for Hessian fly control. In the past, we’ve only seen less than 20 days effectiveness from seed treatments. I’m more confident in longer residual for seed treatments given our experimental results and using the highest labeled rates. So you should only consider the spray as a rescue treatment, last-ditch effort.
4) Pyrethroids seem to work the best to reduce egg number. Graph below.