| ||What is cutting my wheat stems?
Wheat plants falling over late in the season may be due to the wheat stem sawfly larvae cutting the stem. Look inside the stem near the bottom of the plant for a long slender brownish cocoon. This is the larvae of the wheat stem sawfly. Larval feeding in the stem can reduce the yield and quality of the grain due to nutrients not being able to reach the head. The larvae can also cut the stem completely, which can cause the plant to fall over and not be picked up by harvest equipment. Thick stands may hide the severity of the damage by holding up the cut stems until the wind blows them down.
What does the wheat stem sawfly look like?
The adults are small, black, wasp like insects with three yellow bands around their abdomen. They can be found resting on grain stems, head down, starting in June. The larvae are a pale yellow color with a brown head and a blunt pointed projection on the tail end. The larvae can be found feeding inside the wheat stems, and will make an S-shape when removed. Also characteristic of the wheat stem sawfly larvae is the sawdust looking frass (larval feces).
What is the lifecycle of the wheat stem sawfly?
The over wintering larvae pupate in May and in June the adults emerge and start to lay eggs. Egg laying continues into July with the newly hatched larvae starting to feed. In August the feeding continues with the larvae making their way to the bottom of the stems, where they will turn around, cut the stem, plug the top with frass and leaf material. By September the larvae are in a cocoon to over winter in the stems of the wheat. There is only one generation of sawfly per year.
What are the thresholds for wheat stem sawfly?
There is no definite threshold set for wheat stem sawfly, but it is recommended that cropping plans changed if 10-15% of stems are cut the previous year.
How can I control wheat stem sawfly?
There are no chemical control methods for wheat stem sawfly. The best strategies are to seed solid stemmed varieties of wheat, or rotate to oats, barley and broad-leaved crops. Sawfly will lay eggs in the barley, but the larvae do not usually live long enough to do any damage. Swath infested wheat as soon as the kernel moisture drops below 40% to save the stems before they are cut and fall over. Straight cutting would leave the crop standing longer, making it more susceptible to being cut and therefore unharvestable.
Insects sometimes confused with wheat stem sawfly:
|Wheat stem sawfly||Wasp like, 8-13mm long, black with three yellow bands around abdomen||Pale yellow to cream colored, wrinkled and s-shaped with a brown head and blunt projection on the tail end- 13mm when full grown|
|Hessian Fly||Mosquito like, 4mm long||Newly hatched reddish-orange with a translucent green strip down back. They will turn white as they mature, pupa look like flax seeds|
|Wheat stem maggot||Yellowish white flies 3-4mm long with three black stripes on thorax.||Slender, green , spindle shaped that are tapered at both ends. Pupa slender and green.|
Wheat Stem Sawfly
Wheat Stem Sawfly- Saskatchewan
Prepared by Lisa Adam, Ag-Info Centre, Alberta Agriculture and Rural Development