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Soybean Aphid 07/16/02 7:00:58 AM
SOYBEAN APHID July 15, 2002
Michigan has now confirmed the presence of soybean aphid in their fields. Ohio has not but extension people there believe it is only a matter of days since surrounding states are finding them. So far, there have been no confirmed reports in Ontario. The next 2 to 3 weeks is a critical time. If infestations are delayed until well after flowering, no control measures may be need. The larger plants are more tolerant at that stage. Thus, it is essential that growers be checking for large populations of aphids throughout the rest of July. Where soybean aphid occurs in large numbers, most people should have no problem making the correct identification. If soybean aphids are found, please contact OMAF field crops entomologist Tracey Baute in Ridgetown at 519-674-1696 with the date and location.
For determining the need for treatment, the following is a procedure recommended by Ohio State University Extension personnel.
Sample the upper leaves from 4-5 plants from 20 locations in the field, and rate the aphid infestation on a scale of:
0 = none
1 = 1-10 per single leaflet
2 = 10-30 per single leaflet
3 = 30-100 per single leaflet
4 = 100-300 per single leaflet
5 = >300 per single leaflet
An average rating of 3 or higher across the field suggests that soybean
aphids are common and abundant, and treatment should be considered. At a rating of 3 or higher, you will probably also find aphids on the petioles and stems that suggest an increasing population. If honeydew is present in the field and noticeable, the aphid population is probably high.
Observations from Ohio and other states last year suggest that the greatest benefit from an insecticide application will come in July during flowering or immediately thereafter. The later in the summer an insecticide application is made, the less the benefit from that spray. Spraying late in the season after pods have filled or following dispersal of winged aphids in mid-to-late summer will be too late to prevent economic yield loss.
Hopefully, here in Ontario, we will be well into pod fill before large numbers of aphids are found. If you do find aphids and are wondering about spraying, please don’t hesitate to call your Co-op branch for recommendations.
Mike Dick
Crop Specialist, Stoney Point Co-operative
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