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| Most aphids will be found on the lower side of the leaf surface. |
Go to the following pages to study:
Description, identification, and the life cycle of soybean aphid
Symptom and signs of soybean aphid activity
Agronomic impact of soybean aphids
Scouting soybean aphids
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Management of the Soybean Aphid
Flowering (R1) and early pod fill (R4) seem to be critical times for aphid control. However, infestation as early as V1 was observed in 2003. This long scouting window and the re-distribution of aphids among fields as the summer progresses makes repeated visits a necessity. Dry conditions are likely to increase aphid induced yield losses, while intense rainfall may kill many aphids by dislodging them from the plant. The high humidity that follows rain can increase the potential for aphid fungal parasitism.
Early-planted soybeans may be less susceptible to aphids
Many agronomists have commented that, in general, lower aphid populations can be found in early-planted fields. Although early planting is not considered a fail-safe method in controlling aphid populations, it can be considered another incentive to plant soybeans as early as possible.
Action thresholds
Use an action threshold of 250 aphids per plant if populations are actively increasing. This action threshold should be based on an average of 250 aphids per plant over 20 to 30 plants sampled throughout the field. Regular field visits are required to determine if soybean aphid populations are increasing. Using an insecticide below the recommended threshold is not a very good IPM strategy, and can put you in a worse scenario since all the natural predators are eradicated.
In replicated research trials, this threshold has worked well in late vegetative (right at first bloom) to R4 soybeans. Spraying at or beyond R6 has not been documented to increase yield, especially if the crop has grown well through the vegetative stages.
To determine if an aphid population is actively increasing, check over several visits. Conditions that favor aphid population growth are cool temperatures, plant stress, particularly drought stress, and a lack of aphid predators.
Insecticides
Many insecticides have been labeled for soybean aphid and most of them do a good job as long as the label is followed. Timing is critical (don’t spray too early or too late) and get good plant coverage is important. Threshold levels have been determined for aphids and sprayer specifications such as water volume, droplet size, and pressure must be optimized to move the insecticide down in the canopy to get the maximum out of the application.
Two factors need to be considered when treating aphids with an insecticide: percent controlled and the length of time the plant is protected. Both factors are influenced by the product and rate. Pyrethroids (Asana, Baythroid, Mustang Max, Warrior) tend to provide longer residual than cabamates (Furadan) and organophosphates (Lorsban). On the other hand, organophosphate exhibit a vapor action that help in dense canopies or at high temperatures (>90ºF). Aphids are relatively easy to manage and any labeled product should provide adequate control.
If high populations persist into late August, re-treatment may be needed regardless of the product and rate. A final factor that needs to be considered in late season aphid treatment is the pre-harvest interval (PHI) of insecticides. Current insecticides labeled for soybean aphids have a PHI between 21 and 60 days. Insecticide seed treatment is now also available which can help minimize early infestation of soybean aphid. It is important to recognize that the residual effects of these insecticide seed treatments does not last forever (up to 6-7 weeks) so scouting should still be a priority.
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Estimate lady beetle populations at the same time you estimate aphid populations. |
Be aware of aphid natural enemies
Soybean aphids have numerous natural enemies that play a key role in suppression of the soybean aphid. When a small aphid population is found in the field (below threshold), do not use insecticides since natural enemies may suppress the aphids.
The multicolored Asian lady beetle appears to be one of the most common natural enemy. When estimating aphid populations, it would be valuable to estimate lady beetle populations at the same time.
Other predators and parasites that attack aphids include lacewing larvae and predatory bugs. Evidence of parasitic wasp activity is the presence of aphid mummies on leaves scattered through the aphid colonies.
Natural parasites may be the future solution for soybean growers in the United States. Aphid parasites have reduced the soybean aphid in China and Japan to be only a sporadic pest today.
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