It’s time to start scouting soybeans to make sure soybean aphids are not reaching threshold. A few fields that my crew has been monitoring have continued to rise in aphid numbers and are getting closer to threshold. There are natural enemies present though and they could still win the battle. We’ve seen some fields with lots of parasitized aphids (mummies) and lady beetles that have taken down most of the aphid colonies. But this may not happen in every field. Scouting on a regular basis will help you determine if the very important natural enemies can keep up or if the aphids win the war and reach threshold.
It’s been a while since some of you have had to spray your fields so I thought I’d remind you of the threshold. The threshold is “250 aphids per plant and increasing on 80% of the plants during the R1 (first flower) to R5 (beginning seed) stages.” This doesn’t mean that you need to spray as soon as you reach 250 per plant. The actual injury level where the yield lost is equal to the cost of control is closer to 660 aphids per plant. So between 250 and 660 you have a window of time to determine if the natural enemies will save you from spraying or not. Remember, if you spray the fields prematurely, the natural enemies will take longer to build back up in numbers and the aphids will have essentially won with your help. Only when the aphid populations continue to increase towards 660 per plant do you know for sure that the aphids are winning and that they need to be sprayed.
To help you identify the different natural enemies that you may come across when scouting, here is a link to the Soybean Aphid Scouting Card – ENGLISH. For chemical control options, refer to the Field Crop Protection Guide, OMAFRA Publication 812 at: http://www.omafra.gov.on.ca/english/crops/pub812/2aphid.htm
Big Exciting News – Keep an eye out for a smartphone app being developed by OMAFRA and U of Guelph that is due out in the next few weeks. The “APHID ADVISOR” will be available on blackberries for this year (others to come in the next few years) and will help you decide whether you need to spray your field or not. It stems from the dynamic action threshold work done by Rebecca Hallett et al. at the University of Guelph. It takes into consideration the ratio of aphids to natural enemies you are finding and determine if there are enough natural enemies to not have to spray. I will make an announcement here when the app is ready for use and will give you a bit more details about it then.
In the meantime, happy scouting on these nice summer days.