Baute Bug Blog

It has been a few years for some since they have had to worry about soybean aphids, let alone make a spray decision.  So I want to cover off the key points you need to know through some of the repeat questions that have been coming in.  Anyone with more questions after reading this, please ask in the comment sections so we can all continue the discussion there.

Q1.  With soybeans at $15, does that threshold change?  Answer:  No. The economic threshold of “250 aphids per plant and increasing on 80% of the plants in the field during R1-R5″, already takes into consideration a wide range of soybean prices.  The actual economic injury level (where the cost of control is equal to the damage they are causing) is around 660 aphids per plant.  So you have a large buffer area between the threshold and the economic injury level to determine if a spray is needed.

Q2.  Isn’t it getting late to spray for aphids?  Answer:  No. Soybeans are susceptible to aphid injury from R1 (first bloom) all the way until your crop reaches R6 (Full Seed – when the pods at the top of the plant have seeds filling the cavity of the pod).  Once it is in the R6 stage, you need a lot more aphids (over 1000/plant) to see any yield response.  And you need to be cautious as you approach R6 as you are also close to approaching the pre-harvest interval aka days to harvest limit for the products registered   But much of the soybean crop still has a ways to go before reaching R6 so please keep scouting.

Q3.  I have a field that has been fluctuating from 100 to 400/plant and back down over the last few weeks.  Do I need to spray?  Answer:  Most likely not -but keep watching. The fact that the aphid populations keep fluctuating in this fields is a good thing.  It indicates that the natural enemies are helping.  Plus the cooler night temps are not as ideal for the aphids so their development is going to slow down a bit, allowing for the natural enemies to keep up.  If the crop is not stressed (i.e.  it has been getting a decent amount of rain and is lush) you can hold off to closer to the ECONOMIC INJURY LEVEL before you need to spray.  So only if you see these fields hitting 500 or more and are staying at that level might it still be worth spraying.  Again, make sure the crop hasn’t reached R6 yet.  Any fields that are really stressed from lack of moisture (and I know there are some out there) need to stay closer to the 250 threshold and increasing  (but not below that number).  If populations keep fluctuating from 100 to 300 and back down, even these fields may not need to be sprayed.  As long as populations fluctuate, it is a sign that the aphids aren’t getting the upper hand.

Q4.  I am seeing 150 aphids per plant.  Should I get out and spray now and get ahead of them?  Answer:  Absolutely NOT. The threshold of 250 per plant and increasing is there for a reason.  You are not losing yield equivalent to the cost of the spray until closer to the 660 aphids per plant.  At 250 aphids per plant and below, there is a lot of opportunity for natural enemies to keep up with the aphid populations and provide you with free biological control.  If you spray too early, you kill these natural enemies off and give the aphids the freedom they need to build up more rapidly.  You will never get 99% control of the aphids but you are likely to get that good of control of the natural enemies.  Even if 10% of the aphids survived a spray, they will easily build up again in the absence of their enemies.

Q5.  I saw a Speed Scouting Aphid App recently launched out of the US.  Is it something we should use here?  Answer:  Unfortunately No. Nothing against my US counterparts who developed this concept.  But when we tested it here in Ontario in many field scenarios, when the aphid populations were building up rapidly, it did not tell us to spray soon enough and when the populations were building up very slowly, it often told us to spray when we didn’t need to.  So I don’t recommend its use in Ontario.  What I will recommend is the aphid app that we are developing here in Ontario (between UofG and OMAFRA).  I am not being biased here.  It is called the Aphid Advisor.  We are in the final testing phase this week.  Currently it is only for blackberries but if it is successful, we will be working on getting it for the other smartphones in use.  It does still require you to do the full plant counts on 10 random plants in the field but it also has you punch in the number of natural enemies hanging out on those plants.  Based on the forecast for your area (determined by the location you enter) and the ratio of aphids to natural enemies you are seeing, the app will tell you if you need to 1) Spray, 2) Wait and Watch or 3) Don’t spray.  It is based on the dynamic action threshold work that Rebecca Hallett et. al. did the last few years at U of G. We tested it in the field and it really does help to determine if the aphids are going to win the battle over what natural enemy population exists in that field.  It takes care of that grey area between the 250 to 500 aphids per plant range where you are uncertain as to whether you need to spray or not.  So keep an eye out for that launch expected in just a matter of days.  And we will be on display at the OMAFRA/OSCIA tent at the Outdoor Farm Show for all to try out.

If you want any more information on soybean aphids, here are a few helpful links:

Agronomy Guide for Field Crops – Soybean aphids: http://www.omafra.gov.on.ca/english/crops/pub811/13soybean.htm#soybean

Field Crop Protection Guide – Soybean aphids control options: http://www.omafra.gov.on.ca/english/crops/pub812/2aphid.htm

Soybean Aphid Scouting Cards:   English  http://bautebugblog.com/wp-content/Soybean-Aphid-Scouting-Card-ENGLISH.pdf French  Soybean Aphid Scouting Card – FRENCH

Reports are coming in late last week of fields in Eastern Ontario reaching well above threshold levels for soybean aphids.  Just a few weeks prior, these fields had only 30 to 40 per plant.  I suspect other fields in even Central and Southern Ontario will also experience this kind of rapid increase as daytime and more importantly night time temps are now back down to a level that is more ideal for these aphids.  If not enough natural enemies are there to take them down, the aphids reach threshold quite quickly.

Scouting soybeans at least once a week from now until fields are into the R6 stage is advised.  Particularly since other pests are also active in the fields now including spider mites, defoliators like Japanese beetles, red-headed flea beetles and bean leaf beetle which the latter are also starting to feed on the pods and clip some pods off plants in some fields.

Besides…aren’t soybeans a lot easier to scout than corn fields this time of year?  Just saying….. 

There is a lot happening out there. I am sure I am not aware of half of the infestations that are going on but at least I will report on what I do know.

Western bean cutworm - Hot spot egg mass locations continue to be in the Bothwell area with now fields in the Tillsonburg area also showing up with significant pressure.  Many other fields in southern Ontario have a low number of egg masses in them right now but with moths numbers continuing to climb in our traps, I suspect more egg laying will take place this week and next.  Unfortunately much of the corn crop is in the ideal growth stage to attract moths to lay eggs.  Scouting is advised.  Do not make a spray decision without scouting the field first to know that you are at or above threshold.  Moths are still coming in and premature sprays may miss the peak egg laying in your field.  We will let you know when peak moth flight occurs (last year it was next week but I suspect we will be a little behind this year).

Soybean aphids - Hot spots of near to over threshold infestations have shown up, particularly in the Shakespeare to Mitchell area.  Also north of London near Arva and Ilderton.  Most of higher infestations are in fields that were planted early without Cruiser but even early fields with Cruiser are now seeing populations start to build.  Over the last two weeks, many other early and late planted fields distributed across Ontario have aphids in them now (too many to list).  This is the second wave so to speak of aphid infestations where summer migrants have moved in from other regions to start colonies in new fields.  If they arrive in fields with few predators, populations can rise quickly.  Fortunately this very hot weather should slow the aphid development down, particularly since crop canopies have not full closed in many cases to make it cooler.   But this doesn’t mean they can’t get out of hand on you.  Plus the crop is extra stressed right now so spraying closer to just past threshold is advised (if predators are not in great numbers) rather than waiting to get closer to 500-600 aphids per plant which is acceptable in a healthy stress free year.

Spider mites - I have not heard of any reports of spider mites yet but they have got to be out there.  In both soybeans and even seed corn, I expect to see mites flare up quickly with this hot, dry weather.  Look for signs of plants along the fields edge turning bronze and looking somewhat sand blasted.  Look for mites on the underside of those leaves.  Spot sprays along the fields edge where these mites are starting up can often keep you from having to spray the entire field.

Keep in mind daytime temps are extremely hot for applying most insecticides.  You are better off waiting to the end of the day when temps cool down if spray is warranted.

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.

It hasn’t been since 2002 that we have experienced this low of levels of soybean aphids.  Cross my fingers and knock on wood but I think we are going to get through the season without a problem.

That said, spidermites are starting to pop up in fields, particularly where it is starting to get a bit dry.  Scout perimeters and keep an eye out for plants and leaves that are bronzing or look sandblasted.  It is too easy to miss the mites and suffer a serious yield loss because of it.  Even the aphids don’t like to live on the mite infested plants!