Baute Bug Blog

A recent summer migration of soybean aphids in Ontario has resulted in many new fields having a fair number of aphids in them now.  Fields that were scouted a week or two ago and were found to have very few aphids could now be closer to threshold than you think.  Scouting is advised.  Scout Cruiser treated fields too as we are starting to see some of these fields also nearing threshold now.

Admittedly some people got lucky.  Some of the fields that were infested earlier this year and were rising in numbers are the ones that the aphids developed wings in and left so they may have dropped in numbers and no longer need to be sprayed.  But again, scouting is advised to determine which fields this migration has impacted, good or bad.

Recent soybean aphid scouting maps for Ontario can be found at: http://sba.ipmpipe.org/cgi-bin/sbr/public.cgi?host=All%20Legumes/Kudzu&pest=soybean_aphid 

This weeks map will also go up on the OSG site later tomorrow (Friday Aug 7th) at: http://www.soybean.on.ca/aphids.php

Good luck!

SPIDERMITES: I have a sneaking suspicion that spidermites are making their way into those fields that haven’t had rain in a while.  We have had situations in the past where not only have they popped up in soybeans and were being disregarded as “drought stress” symptoms but also in seed corn, especially around or just after wheat has been harvested in the area.  Be particularly careful in watching those fields that may have had a pyrethroid used recently for any other insect issues.  Pyrethroids do not work on spidermites and can actually cause mite populations to flare up.  For more info on spidermites and scouting, refer to: http://www.omafra.gov.on.ca/english/crops/pub811/13soybean.htm#spider

SOYBEAN APHIDS:  As suspected, some fields are noticing a drastic decline in numbers, while others have seen a drastic increase.  A significant soybean aphid flight took place this week (as captured by our suction traps) and some winged aphids left the early planted fields they started in this summer and have moved to later planted fields either nearby or in other regions entirely.  But we also may have received aphids from neighbouring states and provinces so fields should be checked soon to figure out if you were one of the lucky ones or not. 

 WESTERN BEAN CUTWORM:  We experienced an increase in moth captures this week, indicating that this is a good time to start scouting for egg masses, especially at trap locations that have been catching moths into the double digits.  Since corn is still barely tasseling, the moths will prefer to lay their eggs in corn still.  Trap capture maps for this week are at:  http://www.cornpest.ca/default/index.cfm/wbc-trap-network/weekly-maps-of-wbc-trap-catches/

Information on how to scout for egg masses and larval activity can be found at: http://www.cornpest.ca/?LinkServID=3FD7CC42-65B8-8CF0-A092D60341F09626&showMeta=0   Make sure to click on the speaker notes at the top left of each slide for more detailed information.

Also here is an infosheet on WBC in corn:  http://www.cornpest.ca/?LinkServID=D23DD4EE-188B-3AFA-0809F13CA830D6F4&showMeta=0

Have a Fantastic Long Weekend Everyone!

A lot of calls are coming in this week from growers and reps who have fields that are hovering around the 250 aphids per plant range.  With the poor weather and wheat harvest some are anxious to make the call if they need to spray.  In fact, there are some rumours out there that some are spraying before the field reaches 250 aphids per plant.  I stongly DISCOURAGE this as I have witnessed many times that this does not save you a spray or your time but in fact increases the chances that you will need to spray again in the next 10 days or so because of the natural enemies that were making an effort were instead killed off, leaving the aphids that survived to live well and prosper.

The best way to increase your chances of only having to spray once is to spray well within the threshold, when you have been able to assess that the aphids are definetly on the increase past 250 per plant.  

Here are my best recommendations for the current situation:

1)  In regions where the fields are quite dry and the crop is appearing stressed, plan to spray just above 250 aphids per plant, after you have confidently determined that the aphid population is actually on the increase.  This indicates that the natural enemies are not keeping up and are no longer valuable enough for you to save.

2) In regions where there have been some timely rains and the crop is not stressed, plan to spray when the aphids start to reach around 400-500 aphids per plant.  The economic injury level (when the cost of spray is equal to the cost of control) is around 600-700 aphids per plant.  In a healthy crop you can be a bit more patient and wait to see if the natural enemies kick it in gear and lower the aphid population.  But experience has shown me that once you start to crack the 400-500 aphids per plant mark, there is less of a chance that there will be enough natural enemies and time for them to keep the aphids from reaching the economic injury level.

And keep an eye out for SPIDERMITES, especially in the regions that have not had these rains.  Wheat harvest is starting and spidermites will be moving into soybean fields.  Timely rains help manage them but not every field has had these rains. 

Please let us all know if you are starting to see spidermite injury in your area!

This is a ladybeetle larvae.  They can be black or a dull grey/purple with orange or  yellow markings.  If they are shaped like an alligator, they are a ladybeetle larvae. It will be an adult ladybeetle soon.  Both the larvae and adults feed on aphids.

The black velvet coloured aphid on the right is a parasitized soybean aphid.  It is dead because a tiny wasp has laid its egg inside the aphid and the young wasp has eaten the aphid from the inside.  The adult wasp will emerge from the aphid soon to parasitize other aphids.

 The white flakes in this picture are cast skins of the aphid.  They are NOT dead aphids.  Aphids need to shed their skin to grow so they leave behind what looks like dandriff on the plants.  Do not use these to count or determine if the aphids are reaching threshold or are dying.  Only count the aphids that are Mountain Dew coloured.

This is a syrphid fly larvae.  It is also a natural enemy.  It is a blind maggot that crawls around the leaf until it bumps into an aphid and then eats it.

These are just some examples of the natural enemies that may be busy at work in your fields.  For more information on these and soybean aphid management, here is a link to the Canadian Soybean Aphid Scouting Cards: http://www.soybean.on.ca/aphidinfo/uploads/soybean_aphid_scouting_card__english.pdf

High aphid numbers are being found in fields in counties bordering Lake Simcoe (Simcoe, Durham and Victoria).  Spraying has been necessary in many of the fields that have been scouted.  Scouting is advised in all fields in that region, starting first with the fields that were not treated with Cruiser.  Cruiser treated fields should not be reaching threshold yet but could be starting to have aphids colonize in them.  Past 35-40 days after planting the insecticide is no longer toxic to the aphid, but these fields have most likely not had enough time to build up to threshold levels yet.  So if time is limited, scout non-Cruiser fields first, then return to the Cruiser fields to scout on a weekly basis to stay ahead of any situations.