Baute Bug Blog

There are quite few calls coming in from people who are finding either Japanese beetles or redheaded flea beetles in their soybeans, feeding on the leaves.  Though the feeding might be alarming at first, rarely does this defoliation actually reach threshold levels.  Most of the defoliation happens at the top of the plant which is why it is easy to overestimate what damage is taking place.  Soybeans are great for compensating for the defoliation.  Leaves under the ones with holes grow larger to take advantage of the extra sunlight penetrating the canopy thanks to those holes.

Here is an article on assessing defoliation and what the defoliation thresholds are.  It also includes pictures of most of the leaf feeding culprits.

Article: Soybean Defoliators and Thresholds

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?