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Management of the Soybean Aphid
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| Soybean Aphid Management topics |
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Asian lady beetles feeding on soybean aphids.
Photo credit: University of Wisconsin |
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Aphids feed most commonly on the undersides of actively-growing new leaves.
Photo credit: University of Wisconsin. |
Scout once or twice a week beginning in late June or early July. Fields near buckthorn, the overwintering host, may be colonized at emergence and require earlier scouting. In areas without buckthorn, winged aphids migrate from other areas in mid-season. Check 20 to 30 pIants per field. Examine the entire plant, particularly new growth. Scout late-planted fields closely.
- 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.
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. View photos of soybean growth stages at R1- R8 and soybean aphid action thresholds (pdf)
- 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.
- Check for mummies (parasitized aphids) and for winged females. Do not spray if mummies are numerous, or if a majority of the aphids are winged or developing wings, an indication that the aphids will soon leave the field. Read more about aphid natural enemies »
- Plants are likely to be considerably above threshold if stems or pods are covered with aphids and honeydew, sooty mold covers the bottom leaves, and plants are stunted. Insecticide treatment is probably still of value, but the optimal time for treatment (greatest economic return) is past.
- This threshold incorporates an approximately 7-day lead-time between scouting and treatment to make spray arrangements.
- Consider the product choices for your situation. Aphid kill, residual, and yield gains can vary among individual insecticides and application conditions.
- Pyrethroids (Warrior, Mustang Max, Asana, Baythroid) have a long residual, and work best at temperatures below 90°F. Organophosphate products (Lorsban) have a fuming action, and may work well in heavy canopies or at high temperatures.
- Tank mixes of insecticide, fungicide and/or herbicide are not generally recommended. Soybean aphid, disease and weed pests do not all appear at the same time at economically damaging levels so a single tank mix, while convenient, will not provide satisfactory control of all three pest types. Additionally, sprayer specifications such as water volume, nozzle type (droplet size), and pressure must be optimized for each pest situation.
- Good coverage is important. High spray volumes and high pressure help to move the insecticide down into the canopy.
- Adding insecticide to early-season glyphosate application as "insurance" is not recommended unless aphids are at threshold levels and actively increasing.
- Read more about insecticides for soybean aphids »
- Leave an unsprayed check strip to compare against sprayed areas to determine the performance of the insecticide and the value of the treatment.
- Communicate treatment plans to beekeepers. Spraying at early reproductive stages poses a threat to bees. In areas with concern about honey bees, read insecticide labels carefully to determine risk to bees and take necessary precautions (for example, do not apply during hours in which bees are actively foraging).
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