Late Planted Soys at Risk of Soybean Aphids?

I’ve been pondering our planting situation lately and what impacts it is going to have on some of our key insect pests.   We’ve been anticipating this year to be a good soybean aphid year for Ontario.  It was such an extremely low aphid year last year that natural enemies didn’t build up their populations.  So if aphids were to start up colonies this year, they may get ahead of their natural enemies.

So far we know that aphids were found on buckthorn in late May just north of London.  That’s not surprising since soybean aphids often tend to successfully overwinter on buckthorn in certain areas of Ontario.  They spend a few generations on buckthorn in early to late spring before looking for soybeans.  But there weren’t many acres of soybeans planted early enough for them to start up in southern Ontario.  We are searching those early planted fields this week to see what we can find.  But we do know they have been found on soybeans in Eastern Ontario already.  If early planted fields have Cruiser on them, then those first colonizing aphids will be controlled.  If the early planted fields don’t have Cruiser on them, the aphids will start building up in numbers on a few plants in small pockets of the fields.  As they get crowded on those plants, they will redistribute themselves to other plants in the field or fly off to other fields that are more to their liking.  Regardless, it usually takes until the R1 stage or later before any of these colonies build up to threshold levels.  Often the aphids that have started up in these fields start to try to migrate to the later planted fields which are in earlier growth stages.  But early planted soybeans do risk not having Cruiser left in the plant when larger masses of migrating aphids start to try to colonize fields.  Cruiser can last anywhere from 40 to 60 days at best so it doesn’t protect the crop from the typical July migrations of aphids that we experience.  Early planted fields will need to be scouted around the first week of July to make sure they don’t start to build up to threshold levels.

What about later planted soybean fields?  Unfortunately, later planted soybeans can end up taking the brunt of the soybean aphid infestations in the summer.  These fields are going to be at an earlier growth stage (and therefore more attractive) when new summer migrates from either earlier planted fields in Ontario or those carried in from storm fronts from the US move in.  If not protected with an insecticide seed treatment, populations can build up quickly since the natural enemies haven’t made their way into these fields yet.  I recommend using Cruiser seed treatment on any soybeans that still need to be planted.  It will provide protection until at least the middle to end of July and may help reduce the risk of reaching threshold levels of aphids.

Regardless of planting dates and treatments, all soybeans should be scouted this year for aphids anywhere from mid July until early September.  If the weather does turn hot and dry, the crop will be stressed and therefore any aphid populations will need to be managed as soon as thresholds are reached to keep from losing yield.  If weather gets extremely hot, then the aphids may start to suffer too since they do have a temperature limit and stop reproducing in extreme heat.  In an open, short canopy, those high temps could have a negative impact on the aphids too.

I could be wrong..and I hope that I am.  Maybe the aphids won’t amount to much here this summer.  Maybe we will see an influx of natural enemies that will also help us out.  But 2011 has been building up to be a good aphid year and if weather turns hot and dry and starts to hurt the crop, we will need to be extra diligent at scouting.

Any aphid activity or alerts this summer will be reported here through this blog and on my twitter feed.  I encourage you to also share what you are seeing in the comments section too so that we all can stay informed.