Soybean Aphids Reaching Threshold in Many Fields – SCOUT!

Calls have been coming in from several areas across the province reporting fields that have reached threshold and need to be sprayed.  The most recent hotspots include Huron County along lake Huron, Bruce County near Tara, fields north of Barrie, York and Durham and a large number of acres between Belleville and Cornwall.  Just coming back from Eastern Ontario, I think it is safe to say that a lot of fields will be reaching threshold there this week and next.

Scouting is ESSENTIAL!  Fields that were treated with Cruiser did not allow these early season aphids to build up in numbers and therefore are not reaching threshold yet so focus scouting efforts for now on non-Cruiser treated fields.   

Many are asking if they have enough natural enemies to not have to spray.  Currently the only way we can tell if there are enough natural enemies doing their job is to monitor the aphid populations over a period of days.  If the aphid populations are fluctuating up and down around  250 aphids per plant then the natural enemies are keeping up and should be given a chance.  If the aphid populations are moving from 150 to 400 per plant in just a matter of a few days, then this is an indication that the natural enemies are not able to feed on or kill enough of the aphids and a spray is necessary. 

Many of the aphids I have seen this week have wing buds (the 80s shoulder pad look) which means they will be developing wings soon.  These aphids will either move to other plants within the same field or relocate to later planted fields in the area.  They could even get picked up and carried to a different region by the storm fronts headed our way….but that also means that we could receive some from Ohio and Michigan and other states.  When scouting, use a handlens and try to see if the majority of the aphids have wing buds.  If they do, go back to that field a few days later to see if the aphids are winged and are leaving or left or are just redispersing themselves in the field.  It is quite normal for there to be a summer migration of the aphids this time of year and they do tend to prefer later planted fields, rather than sticking around in the early ones they originally colonized.  But scouting these fields is very important to determine if aphids are coming, going or staying for the long haul.