Wheat Stem Sawfly Found In Colorado

Wheat Stem Sawfly Found Infesting Wheat in Northeastern Colorado

The wheat stem sawfly, long considered a severe pest of wheat in Montana and North Dakota, was found infesting wheat along Highway 14 in Weld County in 2010 and again in 2011.  Colorado wheat growers should familiarize themselves with the sawfly’s life cycle, damage and available management options. The sawfly is the number one wheat pest in Montana, causing over $25 million in losses each year.  While it is unknown how important this pest will become in Colorado, it is important to be aware of and to monitor the situation.

Since the beginning of the last century this sawfly has spread south out of Canada into northern Great Plains spring wheat.  In the last three decades, it has become more abundant on winter wheat and spread into southeastern Wyoming and the Nebraska Panhandle.  The sawfly attacks both spring and winter wheat varieties, causing substantial yield loss due to lodging and reduced seed yield.

The wheat stem sawfly emerges in May when field temperatures exceed 50° F.  The females are active for two to three weeks, placing eggs singly in stems, just below the topmost node.  Larvae develop in the stems and gradually work their way downwards, eating stem tissues as they go.  When the stems begin to desiccate the larvae cut a V-shaped notch around the interior of the stem just above the crown and plug the stem just below the notch, creating a chamber where they remain until the following spring.  The stem often breaks at this notch, which leads to the lodging losses.

Effective chemical controls are not available, however, there are several cultural controls that have proven effective at reducing, but not eliminating, infestations.  Tilling wheat fields after the harvest in the fall to loosen the stems and the soil around them maximizes exposure to adverse winter temperatures.  Spring tillage buries the stubble and makes it difficult for adults to emerge.  However, the advantages of controlling the sawfly with tillage are far outweighed by the benefits of reduced tillage.  Trap crops of other cereal grains, such as oats, barley, and rye, planted between the wheat crop and adjacent stubble also have been used.  These crops are attractive sites for egg laying, but are not adequate for sawfly development.  Planting wheat in larger blocks as opposed to narrow strips is another cultural practice that may reduce sawfly damage potential.  This minimizes the amount of field border adjacent to wheat stubble, which is the part of the crop most vulnerable to infestation.  Crop diversification should have a similar effect.  Using solid-stemmed winter wheat cultivars is perhaps the most effective control.  In areas where the sawfly is a recent arrival, wheat breeding programs are beginning to focus on incorporation of the solid stem characteristic into adapted varieties, using both conventional selection and linked DNA markers. The program at Colorado State University also is initiating long term research into novel methods for making the wheat plant less attractive to the sawfly.

For more information on the wheat stem sawfly, including more detailed control options, please visit the High Plains Integrated Pest Management Guide http://wiki.bugwood.org/HPIPM:Wheat_Stem_Sawfly.  If you observe damage or suspect the presence of wheat stem sawfly in your area, please contact your county Extension agent or Frank Peairs (Frank.Peairs@colostate.edu, 491-5945).

WHEAT STEM SAWFLY MINI-SURVEY
NORTHEAST COLORADO

JUNE 9, 2011

Ο Indicates locations sampled with the number of wheat stem sawfly collected/100 sweeps


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