Anyone out there run some strip trials on soybean aphid this year in Ontario? If you have data you’d like to share with us, please send it to my email .
Our research group has also run trials on some new chemistries and early season thresholds. Once the data is compiled, we will let you know what the preliminary results are showing.
Happy Halloween Everyone.
There are a few guys out there thinking that with the cooler nights, SOYBEAN APHIDS will be leaving their fields so they don’t need to spray those fields that recently reached threshold. If aphids are staying at threshold levels 3 or 4 days after the initial assessment, you still need to spray. Only those fields that are dropping in numbers or have reached into the R6 stage and are no where close to threshold can be considered safe from having to be sprayed for aphids. The cool night temps do not guarantee the aphids will leave to look for buckthorn yet. Triggers from plant quality may also determine whether they stay or go elsewhere.
HOWEVER other insects are starting to be a problem. IP and seed fields need tending to still. BEAN LEAF BEETLE adults are showing up in high numbers at a few of our sites in both Lambton and Elgin Counties. Fields in other counties could also be at risk. Scout fields to determine beetle presence and look at pods for feeding. I like to pluck about 50 pods randomly in the field, grabbing pods from the top 3rd of the plant without taking the smallest/youngest ones. If 10% of the pods collected (or in this case 5 pods) have feeding scars and holes on the surface, AND the beetles are still active in the field, a spray is required in IP or seed fields if the crop is not reached the middle of R6. Preharvest intervals come into play if you get any deeper into the R6 stage of soys. Look for clipped pods on the ground as well as this should also be included in your assessment. If significant clipping is taking place and beetles are still active in the field, spray is required.
STINK BUGS have also made an appearance at threshold levels in a field in Chatham Kent. Very high numbers were reported by Joe Tomecek and after some discussion it was obvious the field needed to be sprayed. Again, only IP and seed soybean fields are at risk, as stink bugs impact quality by piercing the soybean pod, scaring the seed itself. Control may be warranted in IP food grade and seed soybeans if an average of one stink bug per foot of row or 0.2 bugs per sweep are found during the late R5/early R6 stage of soybeans.
I have had a few calls from some reps and growers who have been amazed and delighted and some who have been frustrated and frazzled this week. But I’m in it with you, believe me. Soybean aphids seem to be very active right now, developing winged generations and have been moving from one field to another for the last two to three weeks. I have had sites that were approaching 200 or more and then the very next week there were barely 20 per plant with a lot more natural enemies present too. In part this drop is due to the natural enemies that are moving in to make the kill. But a stronger influence could be the cooler temps we are starting to experience at night and the desire of the aphids to keep finding later planted fields to finish off in before heading to buckthorn. We tend to still see aphids active in fields until at least the second week of September but this year is a bit of a guessing game. On one hand, the soybean growth stages are behind and have quite a few more weeks to go before maturity, on the other, the temps are starting to make it feel like fall already.
Either way, it does mean that it really pays off for you to at least hold off a couple days before spraying at threshold just to make sure that the aphids are truly there to stay. If you are lucky like some, they may decide to leave and the ones that are left can easily be taken care of by the natural enemies.
Patience is key when it comes to these aphids.
I have been getting more calls this week with people wanting to spray the aphids just to take care of them..even if they are not at threshold. Most realize that the natural enemies are going to get killed but they also assume 100% kill of the aphids and struggle to understand how the aphids can build back up so quickly in that same field.
The problem is, you don’t get 100% kill of the aphids. Even if you get 90% control, which is pretty good control, that leaves 10% of the aphids surviving on the plant. They are baby making machines and can build up their numbers back up to threshold in no time…especially now that you killed their natural enemies too, which are not baby making machines and take about 2-3 weeks to recover. Unfortunately the natural enemies need to find mates, produce eggs again, wait for about a week before hatching, then be larvae for another week or two (and hopefully the larvae feed on aphids) before finally becoming the hungry adults. Aphids are different. They are born pregnant and don’t need to mate. They pop out hungry nymphs that can suck on the plants immediately, just like the adults.
Here is a simplistic example to help get this point across. Let’s say a field is sprayed when there is only 100 aphids per plant. If you got 90% kill, that would leave 10 aphids per plant left surviving, and not many natural enemies left to eat these 10 aphids per plant. Aphids can double their population in 1.5 to 2 days, depending on the temperature. So if you started at day 0 with 10 aphids per plant, Day 2 would have 20, Day 4 would have 40, Day 6 would have 80, Day 8 would have 160 and Day 10 would have 360 aphids per plant. You’d essentially be back up above threshold in less than two weeks time..not saving you any money or time for your effort in spraying too early.
At least wait until you are confident that the aphid population is rising above 250 aphids per plant. That is truly the only way to know whether the natural enemies are not doing their job and that a spray is finally necessary.
Spraying before the threshold, grinds all of your biological control to a complete halt, when they may have actually been the ones making a difference. Otherwise, wouldn’t every single soybean field in Ontario need to be sprayed every single year?
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.
First off, I apologize for not updating the blog for the last little while. I’ve been busy with setting up the SouthWest Diagnostic Days and just ran out of time. But let me catch you up on a few things that have taken place but I am also hoping that others who have been out in fields more than I this week can send their comments in on what they are seeing.
SOYBEAN APHIDS - Looks like we have a few fields out there that are reaching above the threshold of 250 aphids per plant and increasing, present on 80% of the plants as they enter the R1 stage soys, particularly in Eastern Ontario (Stomont, Dundas and Glengarry counties) and Southern Quebec. Spraying has been taking place over the last week in Eastern Ontario. Now that most of the soybeans are in or are about to hit R1 across the province, scouting should be done at least once a week to assess what the aphids and natural enemies are doing. Many of the fields are in good shape with timely rains and lots of natural enemies but others are starting to feel the stress from lack of rain and fluctuating temps.
WESTERN BEAN CUTWORM - A few moths have now been found in Ontario through our trapping system. So far moths have been caught in Essex and Chatham Kent Counties (only 1 moth in each of 4 traps). Any trap participants out there are asked to send in their information in on a timely basis so that we can continue to report and map these captures. We will keep you informed on any increasing levels of captures and “areas of concern” that may need to be scouted for egg masses and potential damage.
That’s all for today! Please send in your comments on what you are seeing out there so that we can share that information.
