We just wrote about this topic in our July 16th issue of The Bean Report but felt a revisit was needed. While we have received no reports of aphid infestations requiring insecticide interventions thus far, we have received reports of aphid numbers per plant starting to noticeably increase in some fields with as many as 100 aphids per plant reported in some cases. This gives us pause as we are in the middle of the susceptible growth stages in our soybean crop. To review:
Not a field, a battlefield!! – Remember that soybean aphid scouting is about monitoring the ongoing battle between the soybean aphid enemy and our allies – the natural predators. We only want to go forward with the insecticide option if our allies have lost the battle.
Accurate scouting means repeated field visits – We want to track soybean aphid numbers to see if they are rising, stabilizing or falling and we can only do that by scouting a field at least three times at intervals that vary from a week to 24 hours apart depending on how rapidly the situation is changing.
Remember the action threshold and stick to it – The action threshold (AT) or economic threshold for soybean aphids is 250 aphids per plant and rising. This thresholds represent one of the most thoroughly researched and verified thresholds in the agricultural industry. They work and no halving or quartering of the thresholds are required or valid.
Train you eyes for aphid number estimating – The best way to count soybean aphids efficiently is to train your eyes for estimating the numbers seen per leaf. There are a lot of good resources available online to help you become an accurate and rapid estimator of aphid numbers.
Take enough samples – Multiple samples are needed across at least half of the field. Shoot for sampling between five and ten spots per field and doing counts on six to ten plants pers spot. The more samples you take, the better the call you will make. Pull plants and inspect them thoroughly including the undersides of leaves and the stems. Remember that a few “hotpots” with high aphid counts around the edge of a field does not constitute an infestation.
Monitor the plants and the predators – Whenever entering a field to scout, let your hands move through the plants as you walk. You are looking for the feeling of stickiness which tells us we are dealing with aphids. Also, remember to do an inventory of natural predators to get a handle on how the predator numbers are changing relative to soybean aphids numbers.
Click Here for More on Soybean Aphid Scouting
Click Here to Access Government of Canada Publication A52-170E “Soybean Aphid Scouting Card”