By Brian Hefty
Soybeans used to be so easy to raise. We didn’t seem to have disease or insect issues, but now we do. We have sprayed every acre of soybeans on our farm for 12 years in a row for soybean aphids. That’s the bad news. The good news is our yields have continued to go up as long as we spray early, and the treatment only runs $2 to $4 an acre. In other words, it could be a lot worse.
As I analyze this aphid thing, it really comes down to 3 segments: scouting, the threshold, and product choice.
SCOUTING – Scouting for aphids isn’t super easy because there are always hot spots. You walk along finding 20 or 50 per plant, and then you hit an area in the field with 1000 per plant. Nevertheless, you’ve got to scout and scout often because keep in mind aphid numbers can double in a day. They like relatively dry conditions and an average temperature of around 77 degrees. Let me put this in numerical terms. If numbers can double in a day, here’s what they can turn into just 5 days later if they start at 10 per plant: 20, 40, 80, 160, 320 (just 5 days after you counted 10 per plant). Doubling daily doesn’t always happen, but it can and quite often does, so make sure you are scouting often.
THRESHOLD – after all these years, you probably know that we adamantly disagree with the 250 aphid per plant threshold. Our research and that done by South Dakota State University has found the ECONOMIC threshold to be much lower. Consider this. When the 250 threshold was established, soybean prices were about half what they are today, yields were lower, and treatment costs were almost double what they are today. By very definition of an ECONOMIC threshold, the 250 number should be significantly less when all the ECONOMIC factors have changed. I don’t know exactly what your threshold is because I don’t know your exact economics on your farm; but on our farm, we spray when we find somewhere between 10 and 30 aphids per plant at the R1 to R3 stages.
PRODUCT CHOICE – There are 3 somewhat unique choices you will probably consider:
- Cheap yet effective – Silencer or Declare. Full rates run around $2 per acre.
- Quickest knockdown (and a spider mite killer) – Lorsban (or generic Lorsban). 1 pint to 1.5 pints per acre could cost $4 to $8.
- Spider mites plus aphids with a pyrethroid – Fanfare (that’s generic Capture). This will run $1 to $2 per acre more than the cheap pyrethroid option, but if spider mites are a concern, it’s well worth the money.
If you want, you can buy combinations or make your own combo if you prefer. Cobalt combines pyrethroid with Lorsban, for example. Personally, I’m fine spraying one of the products above, but using 2 modes of action has its merits. However, we don’t like ALL 2-mode insecticides. Bayer, Valent, and Syngenta don’t like it when I tell you NOT to use their Leverage, Belay, and Endigo products, respectively, but here’s the reason why. You have undoubtedly read about bee health and how Europe is banning neonicotinoids. The neonicotinoid family includes Poncho, Gaucho and Cruiser; and the neonicotinoid family is used as a seed treatment on most corn and soybeans in the U.S. because it is quite safe to the environment when used in that fashion. It is also systemic and very effective on many harmful insects. If we lose the neonicotinoids, the average U.S. yield of corn and soybeans will, in my opinion, absolutely go down because there is no good alternative. Anyway, the likelihood that a seed treatment would hurt bees is awfully slim. However, since Leverage, Belay, and Endigo all contain a neonicotinoid and will be sprayed post-emerge, there is a much greater likelihood they will kill some bees. If you need those products, that’s one thing; but I don’t feel you need them for soybean aphid control. It’s not a question of efficacy. It’s a question of long-term viability and acceptance of neonicotinoids. On a related note, there are many other factors affecting bee populations more than insecticides, including parasites, malnutrition, and diseases. Nevertheless, we in production agriculture need to steward the products we use to minimize bee deaths.
One last note on soybean aphids: if they damage your plants, even in a small way, your crop is more likely to get diseases, meaning fungicide is more likely to pay. Consider at least trying some fungicide on your soybeans if aphids show up this summer.