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Summer Survey for Wheat Stem Sawfly
Wheat stem sawfly activity has been very quiet in north central and western counties. So far, no significant reports of this insect in North Dakota. Emergence of sawfly adults normally begins in early June. Last year, emergence occurred in late June and early July due to the cooler season. The adult sawfly is a slender wasp, 1/2 inch long and black body ringed with yellow markings.
One method of sampling for wheat stem sawfly is using a sweep net. Research work in Montana during the early 80's indicates that when sweep net samples average 0.2 female sawfly per sweep, 12% cut stems resulted (0.4 females per sweep = 23% cutting). If sweep net samples are taken, determine the percent of females found. Males emerge first; females emerge later. There is no established threshold for adult sawfly for basing treatment decisions. Chemical treatments are not currently recommended. Cultural controls are still the best.
In July, before harvest, inspect fields to determine infested stem levels. Stems that contain a sawfly larvae develop a distinct red to brown band below the second or third node. By determining infested stems, an estimate of potential stem cutting can be made. Heavily infested fields may be swathed to reduce lodging losses.
MANAGING WHEAT STEM SAWFLY:
HARVESTING . . . Swath the most heavily infested fields at 30-35% moisture before significant lodging occurs. This strategy requires field surveys to determine infestation levels. Infested stems have a reddish-brown spot below the 2nd or 3rd node. Examine 50 consecutive stems in a drill row from at least two sites (one near the margin of the field, another near the center). Determine the percent of stems infested at each site. If >6% of the stems are infested, swath to reduce lodging losses within infested sites.
FALL TILLAGE . . . A shallow fall tillage to dislodge stubble and leave it on the soil surface can result in 90% mortality of overwintering larvae. Tillage can be limited to areas where surveys indicated infestations within the field or strip.
CROP ROTATION . . . Plant non-host crops such as oats, flax, sunflower, legumes, and to a lesser extent barley, rye, durum and winter wheat.
RESISTANT WHEAT VARIETIES . . . Solid stem varieties are unsuitable for sawfly development.
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