July 30, 2009
Swath Grain With Heavy Infestations of Wheat Stem Sawfly
Sawfly larvae tunnel inside the stem and interfere with water and nutrient flow
as the wheat head develops. Losses from wheat stem sawfly injury are of two
types:
-
Larval feeding inside stems reduces yield (5 to 15% decrease in total seed
weight) and quality of grain (reduced protein and kernel weight).
-
Mature larvae cut stems and stems may lodge to the ground with wind and the
weight of grain heads, and become unharvestable.
Producers should sample wheat crops and determine the percent of plants infested
by sawfly before harvest. The presence of wheat stem sawfly can be verified by
splitting stems and looking for the S-shaped larvae about to inch long and
cream colored with dark head inside the stem. Another symptom of sawfly feeding
is the presence of sawdust-like frays inside the wheat stem. Infested wheat
stems often have a darkened area on the stem just below the nodes as a result of
the internal feeding from sawfly. This can be used to detect a sawfly
infestation without splitting the stems.
If more than 15% of stems are infested by sawflies, producers should swath the
wheat crop. Producers should swath
sawfly-infested wheat as soon as kernel moisture drops below 40% to save
infested stems before they lodge. If producers decide to swath grain, us a high
swathing height to conserve the parasitoids that attack wheat stem sawfly.
Research from Montana State University has shown that taller residue (at least
the lower 1/3 of the plant) is better for conserving the parasitoids.
If 10 to 15% of the crop was cut by sawfly in 2009, solid stem wheat is
recommended for 2010 wheat plantings. The 2009 NDSU hard red spring wheat
release, Mott has the solid-stem characteristic that has high resistance to
wheat stem sawfly.
