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Wheat Stem Sawfly Lodging (08/31/17)

Lodging from wheat stem sawfly was observed this past week near Grenora in Divide County, northwest North Dakota (Source: Clair Keene, Area Extension Specialist/Cropping Systems, Williston REC).

Wheat Stem Sawfly Lodging

Lodging from wheat stem sawfly was observed this past knodel.2week near Grenora in Divide County, northwest North Dakota (Source: Clair Keene, Area Extension Specialist/Cropping Systems, Williston REC). The wheat producer commented that “It has been a long time since he had such widespread and severe damage due to wheat stem sawfly.” See photos. Dr. Keene found that the lodging was most severe along the field edges; however, there are many areas well inside of fields that have substantial lodging. In the worst affected areas, 50-80% of the crop is down. Wheat stem sawfly lodging also was reported in Mountrail County near Makoti-Plaza, north central North Dakota (Source: T.J. Prochaska, Area Extension Specialist/Crop Protection, NCREC). Last week, Minnesota reported that wheat stem sawfly was causing lodging problems in wheat in Polk County and around Crookston and East Grand Forks (Source: MN Crop News, August 14, 2017).

Wheat stem sawfly thrives in continuous wheat crop systems, and crop rotation is one of the best cultural strategies for reducing population levels. Spring wheat, winter wheat and durum wheat are the primary cereal crops attacked by wheat stem sawfly. The drought may have provided favorable conditions for wheat stem sawfly populations to increase in western North Dakota in 2017.

Swathing prior to wheat stem sawfly cutting the stem or using a stripper header are the only pest management practices that can be utilized in the current year of the infestation. Swathing sometimes is conducted on just the outer one or two swaths bordering the field, if the infestation is heavy in the field edges only. Early swathing prevents sawfly larvae from cutting the stems and reduces yield loss and harvest problems due to lodging.

To determine if producers need to swath fields, sample wheat crops and determine the percent of plants infested by sawflies before harvest. The presence of wheat stem sawfly can be verified by splitting stems and looking for the S-shaped larvae inside the stems. Another symptom of sawfly feeding is the presence of sawdust-like frass (insect droppings) inside the wheat stem. Infested wheat stems often have a darkened area on the stem just below the nodes because of the internal feeding from sawfly larvae. This can be used to detect a sawfly infestation without splitting the stems. However, splitting stems to confirm sawfly infested stems is best.

If more than 15 percent of stems are infested by sawflies, producers should swath or use a stripper header on the wheat crop. Producers should swath sawfly-infested wheat as soon as kernel moisture drops below 40 percent to prevent infested stems from lodging. Stripper headers may be used for straight cutting the crop. This header will pick most wheat stems off the ground. Stems that are not firmly attached will be brought into the combine while stems still firmly attached to the ground will have grain stripped from the stem. Usually the volume of straw run through the combine will be less using a stripper header than straw run through the combine when picking up a windrow. Also, stripper headers will leave the lower ⅔ of stem intact for improved parasitoid conservation.

Next year, producers in wheat stem sawfly infested areas may want to consider growing a solid-stemmed wheat variety like the NDSU release, Mott, which prevents wheat stem sawfly larvae from tunneling in the stem and eventually kills the larvae. Our research found that the newer solid-stemmed wheat varieties have little or no yield drag compared to the yield drag of old solid-stemmed varieties like Rescue. The newer solid-stemmed wheat varieties have yields comparable to the popular hollow-stemmed varieties like Reeder, and have had higher yields than any hollow-stemmed cultivars at test locations with heavy sawfly pressure. Protein content, milling traits and baking quality are excellent in Mott. The most up-to-date information on wheat variety characteristics and performance can be found in the NDSU wheat guide at www.ag.ndsu.edu/varietytrials/spring-wheat.

Solid-stemmed cultivars do not appear to adversely impact parasitism; parasitism levels often exceeded 50 percent in solid-stemmed cultivars. If 10 to 15 percent of the crop was cut by sawfly in the current growing season, a solid-stemmed variety of wheat is recommended for the following planting season.

For more information, please see our NDSU Extension publication E1479 (revised) IPM for Wheat Stem Sawfly in ND.

 

Janet J. Knodel

Extension Entomologist

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