Wheat Insects in 2016

Wheat Insects in 2016 September 1, 2016

The predominant insect pest of wheat in Nebraska continues to be the wheat stem sawfly (Figure 1). We are still going through the 2016 survey samples and will produce a report later this year; however, our 2015 regional survey included the 11 counties of the Panhandle and 13 counties in southwestern and south central Nebraska.

Our surveys show that all Panhandle counties have some level of infestation. Banner, Box Butte, and Cheyenne counties had the highest infestations with more than 90% of sampled stems infested; Deuel had a very low infestation of about 0.1% (Table 1). Some solid stemmed varieties (for example, Warhorse) do seem to provide some sawfly protection; however, their yield will only be competitive with hollow-stemmed wheat under high sawfly pressure.

Some locations continue to see an increase in at least one parasitoid, Bracon cephi, that attacks the wheat stem sawfly. At some locations where this parasitoid appears to have become established (Figure 2), it seems to be providing a remarkable level of wheat stem sawfly suppression. Looking back at our survey data from previous years, we feel that we have evidence that this parasitoid may have begun at least a couple years ago at some locations. With recent support from the Nebraska Wheat Board, we will be conducting more work specifically on this parasitoid in 2017.

Lastly, while we are still evaluating data from this 2016 trial, spring tillage operations (specifically a disc implement operation) does not appear to have an impact on wheat stem sawfly emergence. Managing the fallow border with one or two passes of a disc implement did not seem to reduce adult wheat stem sawfly abundance in adjacent wheat. However, we are still evaluating samples from this trial and will provide a more conclusive result later this year.

Wheat stem sawfly
Figure 1. Adult wheat stem sawfly
Wheat stem sawfly survey results
Figure 2. Estimated percent infestation of wheat stem sawfly, surviving (living and overwintering) sawflies, and sawfly parasitism rate from one wheat field in Box Butte County
Table 1. Percent of live wheat stem sawfly larvae per tiller from at least one field from 11 Nebraska counties in 2011 to 2015.
Banner 40.7 47 52.3 87 92
Box Butte 14.2 36.8 72.3 77.7 94
Cheyenne 13.3 49 62 77 92
Dawes — * 30 30 55 78
Morrill 20.5 27 88.5 73 86
Sheridan 0 0.7 10.5 5 43
Scotts Bluff 84 72 83 84
Kimball 7 41.5
Sioux 2 0 19
Garden 1 1 0 6 2
Deuel 0 0
* — Indicates no surveys were taken in that county in that year.