Friday, August 11, 2017

Wheat Stem Sawfly Causing Problems in Polk County Wheat Fields

Prepared by Phillip Glogoza, Jochum Wiersma and Ian McRae

As wheat harvest moves northward, we are detecting infestations of Wheat Stem Sawfly in fields in Polk County. Recent storms and strong winds have helped bring these problems to front and center.
Farmers have noticed lodged stems, particularly on field margins, where in some cases plants are 100% lodged for 50+ feet from the edge inward. In those cases, the cut stems could be grabbed and picked up in a bundle (Figure 3) and the stubble below was all cut (Figure 4). As we  inspected the interior of these fields, the percent lodging, declined, but there was still evidence of Wheat Stem Sawfly damage.

Infestations have been found in the areas around Crookston and westward toward East Grand Forks. We urge farmers to pay attention to lodged areas of fields to determine if sawfly are a contributing cause of the problem. While driving the combine, lodged stems should be visible from the cab (Figures 1 and 2). 

Infested stems are plugged on the end by the larva for protection from the environment while overwintering (Figure 5). 

Cut stems, if sliced open, reveal the feeding damage and frass left behind by the sawfly larva (Figure 6).

These locations need to be noted so rotation and tillage can be performed to try and break the infestation cycle.

Figure 3. Wheat stem sawfly cut stems were so extensive, the cut stems could be picked up as a bundle on the edge of this wheat field west of Crookston, MN


The Following summaries are for the review of Wheat stem sawfly injury, biology, identification, and management:

UPDATE: NW MN Soybean Aphid Scouting Summary for July 31 to August 8, 2017

Soybean aphid populations continue to increase in west and south central Minnesota, though we are approaching a time when growth stage, day length and natural controls in those fields are likely to lead to declining populations soon. More fields have been treated, BUT not every field is at threshold and scouting to determine treatment needs is highly recommended. 

Also, be sure to follow up treatment by scouting to determine control success. Some of the fields we have scouted in NW MN show lots of dead aphids. HOWEVER, it is not uncommon to see plants where aphids survived, numbering into the 100's on some of those plants. These are fields most likely treated with a Pyrethroid - Organophosphate premix.

Where we have treated research plots with chlorpyrifos, kill has been very good. The only aphids in those sites have been winged, migrating aphids in the tops of plants. Their numbers and their babies have remained low in number and time should be on our side in those locations.

Reports for southern MN can be found at Southwest Minnesota IPM Stuff Newsletter

Comments from his August 10 report:

"Aphid treatment continues and has expanded to some new areas. Fields in the southern part of the state that have higher aphid populations are related to planting date and moisture. The earlier planted, wetter parts of the state as well as some of the extremely dry areas have lower aphid populations. Remember, there are always exceptions."

Bruce Potter 
UMN Extension IPM Specialist

Tuesday, August 8, 2017

Here are three recent updates, all relating to weed management issues:

Assessing and documenting yield loss due to dicamba injury in soybean
by Jeff Gunsolus, Extension weed scientist

Photo 1. Leaf cupping symptoms of dicamba injury in soybean. Photo: Bruce Potter
As we enter August, the big unknown in fields presenting dicamba injury symptoms will be dicamba’s impact on soybean yield. Unfortunately, due to the sensitivity of non-Xtend soybeans to dicamba, injury symptoms are not reliable indicators of yield loss. The level of yield loss depends on exposure at vegetative or reproductive stage of growth, persistence of injury symptoms, and growing conditions post-exposure.